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Colloquia and Special Seminars (since 2016)

 

2016 · 2017 · 2018

 

DateTimeTalk: Colloquium - Special Seminar / internal - external
2018
2018 May 03
14:30

Stephan Geier

(Uni Potsdam)

Hot subdwarf stars in the Gaia era

Being the stripped cores of red giants, hot subdwarf stars turned out to be important markers of peculiar events in stellar evolution ranging all the way from binary star or star-planet interactions to the progenitors of supernovae Ia explosions used to measure the expansion of our Universe. Significantly enhancing the known sample using data from the Gaia mission we will perform the first comprehensive study of this population.

2018 Apr 26
14:30

Christoffer Karoff

(Aarhus University)

Using Sun-like stars and radio carbon to understand past solar activity

The Sun is our closest star and it has been studied in great details for centuries. Fundamental questions however, still remain unanswered. These are questions like: how large flares is the Sun capable of producing? What was the nature of the Sun during the Maunder Minimum in the 17th century and how did it effect the Earth? I will present two secondary approaches in which we can seek answers to these questions: the study of other Sun-like stars and reconstruction of past solar activity through measurements of 14C in tree rings and 10Be in ice cores.

2018 Apr 24
15:30

Special Seminar: Ben Rendle

(University of Birmingham)

Asteroseismology for Galactic Archaeology - from Oscillations to Galactic Structure

Asteroseismology is a powerful diagnostic tool for the determination of accurate stellar parameters, placing tight constraints on masses and radii(~3-10%; ~1-5%) and subsequently on the derived ages (~20-35 %). Standardasteroseismic measurements are made using scaling relations, which make useof the global asteroseismic parameters the frequency of maximum oscillation and the large frequency separation, but what would be possible if all ofthe frequency information were to be used?  In addition, the use of asteroseismology so far has largely been limited to the fields observed by CoRoTand Kepler which lay predominantly within the plane of the galaxy. With the advent of there-purposed Kepler mission, K2, a broader variety of fieldshave since been observed, allowing fresh perspectives ofold problems to be taken. Here I will present the asteroseismic analysis code AIMS and theinitial findings of the K2 Galactic Poles Project, both of which show great promise for the exploiting the potential of K2 and further advancing the field of asteroseismology.

2018 Apr 24
14:00

Special Seminar: Sebastian Lopez

(Universidad de Chile)

New insights into the high-redshift circum-galactic medium from gravitational-arc tomography

I will report on novel integral-field observations of bright gravitational arcs, designed to map the spatial distribution of the intervening CGM at redshifts z~1.  Our observations have  enabled the first tomographic views of individual high-zgalaxy halos inabsorption, and  thus offer  simulations new and independent boundary conditions to constrainthe so-called 'baryon-cycle of galaxies.’

2018 Apr 23
11:00

Special Seminar: Alice Quillen

(Univeristy of Rochester)

Motions of stars just outside the Solar neighborhood

I will show velocity distributions constructed from distance limited subsamples of 1/2 million GALAH survey stars.  The velocitydistributions depend on metallicity, galactic longitude, and whether the stars are viewed in the Northern or Southern Galactic hemisphere. Thedifferences in the distributions imply that moving groups have velocity gradients in the Galaxy.  Their velocity vectors vary by about 10 km/s acrossdistances of only a few hundred pc.  The phase space substructures and gradients are surprising as they are more complex and stronger thanenvisioned.  I will discuss dynamical processes in the Galactic disk and how they might leave imprints in local velocity distributions.

2018 Apr 19
14:30

Michelle Collins

(University of Surrey, UK)

Using the faintest galaxies as probes of dark matter and galaxy evolution

The dwarf spheroidal galaxies of the Local Group represent the smallest scales on which galaxies are able to form. As such, they are excellent probes of galaxy formation physics. They are also interesting laboratories for understanding dark matter, owing to their large mass-to-light ratios. In this talk, I will highlight how we can use these smallest of galaxies to both test the cosmological paradigm, and to better understand the processes governing galactic formation and evolution. I will also talk about the connection between Local Group dwarf spheroidals and the new class of ultra-diffuse galaxies, which have been found in cluster environments.

2018 Apr 12
14:30

Philipp Gast

(AIP)

Pre-stellar core formation in supernova remnant-cloud interactions

In the classical picture of star formation starless cloud cores evolve via self-gravitating pre-stellar cores into "Class 0" objects on the relatively long (ambipolar) diffusion timescale. In recent years a more dynamical picture emerged in which shocks play a significant role in creating the primary density compressions. A shocked cloudlet initially close to gravitational instability may then trigger collapse. Here, we investigate whether the strong shock of a supernova remnant can induce the formation of pre-stellar cores in more diffuse interstellar clouds which are far from collapsing under their own weight. For this purpose we perform a set of high-resolution, 3D MHD simulations including self-gravity, a small chemical network and anisotropic heat conduction.

We find that, although high-density aggregations are achieved, no stable (gravitationally bound) cores are formed. This seems to indicate that either a further compaction process is necessary to form pre-stellar cores or ambipolar diffusion being an important process as well.

2018 Apr 11
11:00

Special Seminar: Jakob Nordin

(HU, Berlin)

Using Type Ia supernovae from the Zwicky Transient Facility to constrain structure growth

Type Ia supernovae (SNe Ia) are excellent standardizable candles that are routinely used to obtain ~7% extragalactic distance estimates. Improved standardization techniques have now showed how these can be even further improved, approaching the limit where SNe Ia are truly "standard". Simultaneously, a new generation of wide-field surveys will repeatedly observe the full observable nearby universe. The Zwicky Transient Facility (ZTF) pioneers this development and could provide high quality lightcurves of thousands of nearby SNe each year. I will introduce how SNIa distances are derived, describe ZTF and discuss how SNIa peculiar velocities could be used to derive an unbiased measurement of matter clustering in the z<0.1 Universe.

2018 Apr 05 14:30

Florian Niederhofer

(AIP)

The Magellanic Clouds - Discovering our Neighbours

The Large and Small Magellanic Clouds (LMC and SMC) are the most prominent neighbours of our Milky Way. They are recently acquired dwarf satellites of our Galaxy and are in the early phases of a minor merger event. The dynamical interplay between the Clouds led to the complex morphology of the two Clouds and the formation of tidal features such as the Magellanic Bridge connecting the two dwarf galaxies, and the gaseous Magellanic Stream. Thanks to its close vicinity (50-60 kpc) and position above the Milky Way disk, the Magellanic system provides a good opportunity to study in detail its morphology, kinematics and resolved stellar populations. Furthermore, the LMC and SMC host a rich system of massive star clusters, spanning a large range of ages, which is not observed in the Milky Way.

In the first part of this talk, I will give an overview of the Magellanic system, including latest results and present scientific highlights from the ongoing near-infrared VISTA survey of the Magellanic Clouds system (VMC), a survey specially designed to study in detail multiple aspects of the interacting pair of galaxies. In the second part, I will concentrate on Magellanic Cloud star clusters and recent discoveries in this field.

2018 Mar 22
14:30

Shaun Cole

(ICC, Durham, UK)

The DESI Bright Galaxy Survey

Construction of the 5000 fibre Dark Energy Spectroscopic Instrument (DESI) is well underway and on schedule to start the DESI surveys towards the end of next year. I will describe DESI, the surveys that will be under taken with DESI and the main science goals of the collaboration. The huge number of redshifts in these surveys offer the prospect of cosmological constraints from large scale structure with unprecedented small statistical errors. The formidable challenge is to make the systematic errors even smaller. With particular emphasis on the incomplete redshift measurements Bright Galaxy Survey (BGS), I will illustrate how realistic mock catalogues are being used to quantify systematics and assess correction techniques.

2018 Mar 21
14:30

Special Seminar: Shu Yuan

(Yunnan Observatories, Kunming, China)

Polarimetry on the New Vacuum Solar Telescope and polarization simulation for future large telescopes

The New Vacuum Solar Telescope (NVST) is a 1 meter visible and near-infrared solar telescope located at Fuxian Solar Observatory (FSO), in Yunnan, China. Due to its excellent daytime seeing condition, NVST pursues its main science targets on the high resolution observations of photosphere and chromospheres of the Sun. High accuracy spectropolarimetry with high spatial resolution is the main research field in which FSO scientist are involved. I wish to give a general picture about the instruments and observational outcomes from this telescope, especially focusing on the telescope polarimetric calibration procedures, which is my main research interest. For both solar and nighttime observations polarimetry is playing an increasingly important role for future telescopes design and operations. A polarization ray tracing technique has been developed in order to characterize the polarization transfer function of the telescope, which is the basis for the further development of a polarization simulation tool in future. I will illustrate the application of this technique in order to retrieve the instrumental polarization of the Extremely Large telescope (ELT) and some other telescopes.

2018 Mar 16
11:30

Special Seminar: John Monnier

(University of Michigan)

Imaging the Surfaces of Stars

Using long-baseline interferometry, we can beat telescope diffraction and atmospheric turbulence to  image stars and their environments with sub-milli-arcsecond resolution.  The Georgia State University CHARA Array on Mt. Wilson boasts the longest baselines of any optical/infrared array in the world and this talk will summarize the major results from the Michigan Infrared Combiner, including the first resolved images of main sequence stars besides the Sun.  We can now also resolve the interacting components of close binary stars, image magnetic spots on active stars, and watch novae explode in realtime.  Taking advantage of recent breakthroughs in infrared detectors and the installation of adaptive optics on CHARA, we hope to soon image the inner regions of planet-forming disks around very young stars.  Lastly, I will introduce the Planet Formation Imager (PFI, www.planetformationimager.org [www.planetformationimager.org]) project -- a next-generation facility that could transform our understandings of planet formation and exoplanet system architectures.

2018 Mar 13
14:00

Special Seminar: Rahul Kannan

(Einstein Fellow, Harvard)

Arepo-RT : Radiation hydrodynamics on a moving mesh

I will introduce Arepo-RT, a novel radiation hydrodynamic (RHD) solver for the unstructured moving-mesh code Arepo. This method solves the moment-based radiative transfer equations using the M1 closure relation. The implementation is fully conservative and compatible with the withindividual timestepping scheme. The scheme incorporates atomic Hydrogen (H) and Helium (He) thermochemistry, which is used to couple the ultra-violet(UV) radiation field to the gas. Additionally, the infrared radiation is coupled to the gas under the assumption of local thermodynamic equilibriumbetween the gas and the dust.  Our tests show that this scheme is more efficient and reaches higher accuracy than previous radiative transfer schemesthat use the M1 closure relation.  The new code is suitable for studying various important astrophysical phenomena, such as the effect of radiativefeedback in driving galactic scale outflows, radiation driven dusty winds in high redshift quasars, or simulating the reionisation history of theUniverse self-consistently.

2018 Mar 08
14:30

Reinhard Genzel

(MPE)

The formation and evolution of star forming galactic disks

I will discuss the results of three major programs of studying star formation, cold gas, feedback and dynamics of massive 'normal' star forming galaxies near the peak of the epoch of galaxy formation (z~1-3). Our observations were carried out with the IRAM Plateau de Bure interferometer and with large instruments developed with significant or leading MPE participation (the VLT near-IR integral field spectrometers SINFONI and KMOS, and the far-IR spectrometer/photometer PACS on Herschel). When combined, those studies clearly show that massive star forming galaxies near the star formation-stellar mass 'main-sequence' were gas rich, highly turbulent and clumpy, disky systems with various degrees of rotational support. Star formation in these galaxies was plausibly driven by continuous, rapid accretion of gas and minor mergers from the cosmic web. The evolution of their disks and central bulges was probably strongly influenced by disk fragmentation and instabilities, as well as by powerful galactic outflows driven from the large star forming clumps and AGN. I will discuss the impact of these new observations on our understanding of galaxy evolution in the early Universe.

2018 Mar 06
10:00

Special Seminar: Diego Bossini

(Padova Observatory, INAF)

Asteroseismology of Red Giant Stars: a Tool for Determining Stellar Properties

Asteroseismology has opened the door to detailed studies of the near-core structure of low-mass stars, which had not been possible before.   Thank to the new constraints it provides, it is now possible to greatly improve our measurements of the basic stellar properties of field and clusters giants observed far across the Galaxy.

Most of such determinations of ages and masses are, up to now, based on simple scaling relations, involving the average large frequency separation (Dnu) and the frequency of maximum power (numax).

In our work we use observed Dnu and the period spacing of gravity mode to set precise constrains on the physics of stellar models: we include these seismic quantities in a detailed grids of isochrones and hence in a Bayesian method of parameter estimation. Tests with synthetic data reveal that masses and ages can be determined with typical precision of 5 and 19 per cent, respectively, down to 3 and 10 per cent when we add independent information on the stellar luminosity.

2018 Mar 01 14:30

Sean Matt

(Exeter)

Developing a Standard Model for the Rotation and Magnetic Activity of Sun-Like Stars

An enormous amount of what we know about the universe and our own place on Earth depends on our understanding of stars. Yet, even for the most familiar stars, there are still major unsolved questions related to rotation, magnetic activity, and mass loss. I will discuss an emerging picture that self-consistently links all of these processes together and to the overall evolution of Sun-like and low-mass stars. This progress is due to large and diverse new datasets, advances in physical models for the loss of angular momentum (which itself depends upon magnetism and mass loss), and the incorporation of these models into long-term stellar evolution calculations.

2018 Feb 22
14:30

Wolf-Rainer Hamann

(Uni Potsdam)

Massive stars, winds, feedback, gravitational wave progenitors

Luminous, massive stars play an important role in cosmic evolution. With their stellar winds and strong ionizing radiation, they have a large impact on their environment. The relevant spectral analysis of hot-star spectra requires adequate stellar atmosphere models. We have developed the  Potsdam Wolf-Rayet (PoWR) model atmosphere code for this purpose, and have performed comprehensive analyses for massive stars of various types (Wolf-Rayet, O- and B-type stars) in our, and other nearby galaxies.

The evolution of massive stars is not yet well understood. One key uncertain factor is the mass loss in different evolutionary stages.  With our spectral analyses we constrain the mass-loss rates of massive stars empirically. In addition, we are developing self-consistent hydrodynamical models.

From the results of the spectral analyses we can quantify the feedback in dependence from stellar parameters. At low metallicities,  as in the SMC, very massive stars are obviously internally mixed and hence evolve chemically homogeneously. We have studied young, star-forming clusters and found that a handful of their most massive stars dominate the ionizing radiation and mechanical feedback.

The mass loss rate during a stellar life also determines how much mass is left at gravitational collapse, and also under which conditions a black hole, or even a close pair of black holes, can form with the high masses observed
in the gravitational wave events.

2018 Feb 16 11:00

Special Seminar: Eduard Muslimov

(Laboratoire d’Astrophysique de Marseille)

Optical design challenges: from mass-production of optical devices to high-precision instruments for scientific research

The presentation is an overview of my past and present activities in the field of optical design and engineering. It will include my studies in the field of development of holographic optical elements and spectrographs design techniques, which I performed as a PhD student at the Kazan National Research Technical University. Also, I'll present a number of design examples developed for the State Applied Optics Institute. It will include devices for a wide market like OEM spectrometers and unique research instruments like a space-borne hyperspectrometer, XUV spectrograph, projection system for a fusion reactor etc. A special emphasis will be made on manufacturing, assembly and testing tasks, practical implementation of the designs, and collaboration with third parties. Finally, I'll present the recent results obtained at Laboratoire d'Astrophysique de Marseille including new approaches to design and description of freeform optics, innovative designs with curved detectors and certain design examples for upcoming missions. The latter are: MESSIER - a fast wide-field telescope for survey of low surface brightness objects; and POLLUX - high-resolution UV spectopolarimeter at LUVOIR space telescope.

2018 Feb 15
14:30

11th AIP Jamboree

Who does what

The eleventh round of speakers:

Thomas Berlok, Wilbert Bittner, Joar Brynnel,
Edoardo Carlesi, Maria -Rosa Cioni, Momen Diab,
Kristian Ehlert, Harry Enke, Manuel Flores-Soriano,
Yori Fournier, Thomas Granzer, Guilla ume Guiglion,
Roger Haynes, Eloy Hernandez

You can download the talks here (pdf, 5.1 MB).

2018 Feb 08 14:30

Pratika Dayal

(Groningen, The Netherlands)

The first billion years of galaxy formation

Galaxy formation in the first billion years mark a time of great upheaval in the history of the Universe: as the first sources of light, these galaxies ended the 'cosmic dark ages' and produced the first photons that could break apart the hydrogen atoms suffusing all of space starting the process of cosmic reionization. As the earliest building blocks, the shapeless ellipticals galaxies that formed in the first billion years also determine the physical properties of all subsequent galaxy populations. At the forefront of astronomical research, the past few years have seen cutting-edge instruments provide tantalising glimpses of such galaxies chaotically assembling in an infant Universe. I will show how this data has provided an unprecedented opportunity to pin down the reionization state of the Universe (at least in its last stages), understand their physical properties, and study the key physics driving their formation and evolution. Finally, I will try to give a flavour of how the assembly of early galaxies, accessible with the forthcoming James Webb Space Telescope and the associated reionization history, can provide a powerful testbed for Warm Dark Matter models.

2018 Jan 25
14:30

Ann Mao

(MPIfR, Germany)

Detecting magnetic fields in distant galaxies with broadband radio polarimetry

Even though magnetic fields play crucial roles in galaxies from sub-parsec to kilo-parsec scales, how galaxies and their magnetic fields have co-evolved since the early universe remains an unsolved fundamental question in cosmology and astro-plasma physics due to the lack of magnetic field measurements beyond the local universe. In this talk, I will first describe how the advent of broadband radio polarimetric observations have revolutionized the field of cosmic magnetism by enabling the derivation of properties of magnetic fields in astrophysical objects that were impossible to obtain previously with narrowband data. I will then demonstrate how broadband polarimetry, in combination with innovative observational methods can allow us to, for the first time, measure magnetic fields in galaxies in previously uncharted redshift regimes. In particular, I will report our record-holder detection of μG coherent magnetic fields in a disk galaxy as seen 4.6 Gyrs ago by taking advantage of gravitational lensing. I will conclude by discussing prospects of upcoming polarimetric surveys to be conducted with Square Kilometre Array pathfinders and the eventual Square Kilometre Array.

2018 Jan 18
14:30

Igor Soszynski

(Warsaw)

One Million Variable Stars from the OGLE Survey

The Optical Gravitational Lensing Experiment (OGLE) is one of the world's largest optical surveys devoted to searching for variability in the sky. In the last year, the project celebrated its 25th anniversary. During its long history, the OGLE survey collected about one trillion individual photometric measurements for more than one billion stars in the Milky Way and in nearby galaxies. These data has led to many discoveries in various fields of astronomy: gravitational lensing and microlensing, extrasolar planets, cosmic distance scale, structure of galaxies, Kuiper belt objects, etc. Variable stars occupy a special position among the most important achievements of the survey. The OGLE Collection of Variable Stars currently contains nearly one million objects of various types and this is the largest set of variable stars ever obtained by any astronomical project. I will present the most spectacular OGLE discoveries in the field of variable stars.

2018 Jan 12
11:00

Special Seminar: Daniel Hölck

(Durham University)

CHOUGH, the Durham high-order AO instrument

CHOUGH is a low-cost, fast project intended as a high-order Adaptive Optics(AO) technology & capabilities demonstrator. It is a narrow-field, Single Conjugated Adaptive Optics(SCAO) instrument that aims to enable high-order AO on the 4m William Hershcel Telescope(WHT), and its principal purpose is for investigating AO in the visible region of the spectrum (R- to I-bands). CHOUGH takes advantage of the infrastructure of a larger AO project, CANARY, which is located on a Nasthmyth platform of the (WHT).  CHOUGH  can also operate as standalone system  In the laboratory where it is currently undergoing sub-system performance evaluation.

2017
2017 Dec 14
16:00

Special Seminar: Marina Battaglia

(Fachhochschule Nordwestschweiz, Windisch, Switzerland)

Multi-wavelength observations of electron acceleration and chromospheric response in solar flares

2017 Dec 14
14:30

Michiel van Noort

(MPS)

Image restoration of solar data using multi frame blind deconvolution

When observing the Sun using ground based solar telescopes, atmospheric turbulence, resulting from heating of the Earths atmosphere by the Sun, usually causes severe blurring of image data in the spatial dimensions. In spite of tremendous progress made in the development of adaptive optics (AO) systems to correct telescope images for this effect, residual image degradations remain a significant factor, limiting the spatial resolution that can be achieved. Multi-Frame Blind Deconvolution (MFBD) is one of a family of numerical techniques that model and remove these residual image degradations, allowing observers to increase the amount of information they can extract from their data. In this talk, I will describe the basic ideas behind MFBD, discuss how the recent increase in availability of computing resources to the solar physics community has helped to significantly increase the usefulness of this technique, and how this has influenced observational techniques, from the design of instruments, to the acquisition, reduction and inversion of the data.

2017 Dec 13
11:00

Special Seminar: Rob Grand

(HITS)

Disc formation and evolution in cosmological simulations of Milky Way analogues

We present insights into the formation and evolution of Milky Way mass galaxies from the Auriga simulations - one of the largest, highest resolution simulation suites of Milky Way analogues, ran with a comprehensive galaxy formation model including AGN feedback and magnetic fields, and capable of producing disc-dominated, star-forming, rotationally supported spiral galaxies - a recent triumph for cosmological simulations. We study the effects of secular and external processes on the chemo-dynamical structure of the disc, and find that although the strength of radial migration scales with the bar and spiral arm strength, it does not affect the vertical structure of the disc; instead, dynamical heating is dominated by bars in the inner disc and satellite perturbations in the outer disc. However, disc kinematics is to a large degree set by the properties of the star-forming gas, which is generally thicker and more irregular at earlier times owing to a peak in gas-rich merger activity and turbulent accretion at redshift ~ 1-2, followed by a disc growth phase. This evolution is in agreement with the ‘upside-down’ formation scenario and ‘disc settling’ seen in observations of star-forming galaxies. Despite this general trend, we find a large variation in disc sizes at redshift zero, which is driven by the diversity in halo angular momentum, merger histories and the strength of feedback. In addition, we find a chemical thin/thick disc in some simulations, and identify two mechanisms for its generation: a “centralised starburst” pathway and “shrinking disc” pathway, the latter of which is new. We conclude with an outlook to future Galactic archeological studies combining these state-of-the-art numerical techniques and upcoming Gaia data.

2017 Dec 07 14:30

Harald Pfeiffer

(AEI Golm)

Gravitational waves from the second observing run of LIGO and Virgo

The Advanced LIGO gravitational wave detectors performed their second observing run between November 2016 and August 2017. During the last month of observations, the Virgo gravitational wave detector joined observations, delivering greatly enhanced sky-localisation of the resulting three-detector network. While data-analysis is still ongoing, three binary black hole coalescences have already been announced, as well as a spectacular coalescence of two neutron stars observed both in gravitational waves and the entire electromagnetic spectrum. This talk gives an overview of these observations, and their implications for astrophysics and fundamental physics.

2017 Nov 30
14:30

Petri Käpylä

(AIP)

Resurrecting the turbulent dynamo: starspots without flux tubes

The solar dynamo has been described for the past two decades mostly in terms of flux transport dynamo models which rely thin magnetic flux tubes that are produced and stored at the base or just below the convection zone. They were thought to rise to the surface, and thus form spots, once reaching a high enough field strength (~100kG). A single-cell meridional flow and a low magnetic diffusivity are prerequisites for the model to reproduce the solar cycle.

Recently the main assumptions in the flux transport models have been questioned by new observational and numerical results. At the same time, increasing interest toward distributed dynamos, which produce much weaker (~1kG) diffuse fields throughout the convection zone, has been rekindled. Arguably the most severe remaining argument against distributed dynamos has been that there has been no mechanims to form strong concentrations of magnetic field, i.e. sunspots, from weak diffuse fields. A promising candidate, the Negative Effective Magnetic Pressure Instability (NEMPI) has since been verified in idealised simulations. I will present results from an ongoing effort to enable spot-formation due to NEMPI with high-resolution simulations of turbulent convection and the implications of the results to stellar dynamo theory.

2017 Nov 29
15:00

Special Seminar: Rainer Weinberger

(HITS)

AGN Feedback in Cosmological Simulations

It is generally believed that feedback from supermassive black holes has a significant impact on the formation and evolution of massive galaxies, galaxy groups and clusters. In this talk, I present our recent progress in modeling these feedback effects in cosmological simulations of galaxy formation that reach ~kpc resolutions and show its effects on the simulated galaxy population. In particular, I will present first results of the IllustrisTNG simulations, a recently completed set of follow-up simulations of the Illustris project, focusing on the effect of AGN on a variety of observables from galactic to cosmic scales. Towards the end, I will give an outlook on how future feedback models in cosmological simulations can be more predictive. I will present a high resolution study of AGN jets interacting with the surrounding intra-cluster medium and show how we can systematically use idealized, high resolution simulations to understand the small-scale feedback physics and to develop more predictive sub-resolution models for future simulation projects.

2017 Nov 23
14:30

Christoph Pfrommer

(AIP)

How cosmic rays shape galaxies

Understanding the physics of galaxy formation is an outstanding problem in modern astrophysics. Recent cosmological simulations have demonstrated that feedback by star formation, supernovae and active galactic nuclei appears to be critical in obtaining realistic disk galaxies and to slow down star formation to the small observed rates. However the particular physical processes underlying these feedback processes still remain elusive. In particular, these simulations neglected magnetic fields and relativistic particle populations (so-called cosmic rays). Those are known to provide a pressure support comparable to the thermal gas in our Galaxy and couple dynamically and thermally to the gas, which seriously questions their neglect. After introducing the underlying physical concepts, I will present our recent efforts to model cosmic ray physics in galaxy formation. I will demonstrate that cosmic rays play a decisive role on all scales relevant for the formation of galaxies, from individual supernova remnants up to scales relevant for entire galaxies. Finally, I will discuss the non-thermal radio and gamma-ray emission of Milky-Way like galaxies and how the next-generation instruments can be used to infer properties relevant for galaxy formation.

2017 Nov 16
14:30

Jochen Greiner

(MPE Garching)

The gravitational wave detection of a binary neutron star merger: expectations, surprises, and prospects

On August 17, 2017, Advanced LIGO & Virgo detected gravitational waves from a binary neutron star merger. A short-duration gamma-ray burst was detected in temporal coincidence by the INTEGRAL and Fermi satellites. A few hours later, an optical/NIR transient was found which turned out to be compatible with the predictions of a kilonova, powered by the radioactive decay of heavy r-process nuclei produced in the merger. I will give an overview of the observational results of this event which will go down in history as the start of multi-messenger gravitational wave astronomy. I will contrast the original expectations with the actual findings, and will spend most of the time on the mismatches, i.e. the new questions which emerged.

2017 Nov 09 14:30

Gaitee Hussain

(ESO)

Stellar magnetic activity in young Suns

T Tauri stars are young (~Myr) pre-main sequence solar-type stars that show signatures of strong magnetic activity from the radio to X-ray wavelengths. T Tauri stars are at a critical point in their pre-main sequence evolution, with many of them still accreting from substantial circumstellar disks - in which planets are presumably forming. Large-scale stellar magnetic fields play an important role in channelling accretion from their disks.

Over the last decade we have catalogued the range of magnetic field topologies found in PMS stars and have been assessing their impact on their accretion states via both observational and theoretical means. In this talk I will review our current understanding about large scale fields in T Tauri stars, showing how their topologies vary as accretion switches off. I will conclude by demonstrating how these same surface mapping techniques can be used to detect and study close-in planets around young PMS stars that have stopped accreting.

2017 Oct 19
14:30

Sofia Randich

(INAF-Osservatorio Astrofisico di Arcetri)

Open star clusters in Gaia and the Gaia-ESO Survey: a revolution in stellar physics and stellar age determination

With the first data release in September 2016 the Gaia revolution has started. I will discuss how Gaia astrometry and photometry, combined with detailed information on radial velocities, astrophysical parameters, and element abundances from ground based spectroscopy, and the Gaia-ESO Survey in particular, are going to allow huge progress in stellar physics research and a full exploitation of open clusters as stellar age calibrators.

2017 Oct 16
15:00

Special Seminar: Emma de Ona Wilhelmi

(Institut de Ciencies de l'Espai)

An energy cutoff in the TeV gamma ray spectrum of the SNR Cassiopeia A

It is widely believed that Galactic Cosmic Rays (CR) are accelerated in Supernova Remnants (SNRs) through the process of diffusive shock acceleration. In this scenario, particles should be accelerated up to energies around 1 PeV (the so-called 'Knee') and emit gamma rays. To test this hypothesis, precise measurements of the gamma-ray spectra of young SNRs at TeV energies are needed. Among the already known SNRs, Cassiopea A (Cas A) appears as one of the best candidates for such studies. It is relatively young (about 300 years) and it has been largely studied in radio and X-ray bands, which constrains essential parameters for testing emission models, such as the magnetic field. I will present the results of a multi-year campaign of Cas A with the MAGIC Imaging Atmospheric Cherenkov Telescopes for a total of 158 hours of good-quality data. We obtained a spectrum of the source from 100 GeV to 10 TeV and fit it assuming it follows a power-law distribution, with and without an exponential cut-off. We found, for the first time in Very High Energy (VHE, E>100GeV), observational evidence for the presence of a cut-off in Cas A. I will discuss the implications of this cutoff on the acceleration of particles in Cas A and how it constrains physical parameters such magnetic field, gas density, etc.

2017 Oct 16
14:00

Special Seminar: Morten Bache

(DTU Copenhagen)

Ultrafast nonlinear optics with quadratic nonlinearities: prospects for integrated photonics

Crystals with quadratic nonlinearities have great potential for ultrafast nonlinear interaction as they offer a parametrical control over the nonlinearity. By operating with a finite phase-mismatch both the sign and strength of the nonlinear phase shifts can be changed. At DTU Fotonik we have over the past decade exploited this to generate a negative nonlinear refractive index. This gives filament-free interaction of high-energy self-defocusing solitons in bulk crystals, and all the associated aspects of a soliton-based supercontinuum: soliton fission, dispersive wave formation, Raman self-frequency shifts and self-steepening. An important recent experiment showed that the supercontinuum content can be parametrically controlled as the soliton though the quadratic nonlinearities can experience phase matching with a dispersive wave deep into the blue and mid-IR, by respectively sum- and difference frequency generation. This gives a new dimension to the control over the spectral content in a  supercontinuum, and this has interesting potential applications for on-chip waveguides for integrated photonics as it allows to coherently extending comb lines to new regions. I will review these possibilities at the end of the talk, where results from integrated photonics platforms using lithium niobate, silicon nitride and aluminum nitride are discussed.

2017 Oct 12
14:30

Eline Tolstoy

(Uni Groningen)

Galactic Palaeontology

I will talk about how resolved stellar populations can and have been used to study the fossil record of star formation in nearby Local Group galaxies. This requires accurate colours, variability, chemistry and kinematic measurements of large samples of individual stars from deep imaging and spectroscopy. These studies provide a detailed picture of galaxy evolution going back to the earliest times, providing insights into the initial star forming properties of the early Universe, and how these have changed over time.

2017 Oct 11
14:00

Special Seminar: Ines Juvan

(Space Research Institute Graz, Austria)

Determining the spin-orbit alignment for an extra-solar super-Earth

Measuring the spin-orbit (mis)alignment for close-in exoplanets can yield information about the planets’ migration history. So far, a wide range of obliquities has been measured, making it yet difficult to identify the main mechanism driving the evolution of close-in objects. Most obliquity measurements have been derived for close-in gas giants, but these values are hardly known for planets smaller than Neptune. In this talk, I will report on our project to derive this property for an extra-solar super-Earth using the starspot tracking method. This project is based on a collaboration between the IWF (Graz, AT) and the AIP.

2017 Oct 09 14:00

Special Seminar: Ewald Puchwein

(Cambridge University, UK)

Cosmic reionization and the thermal history of the intergalactic medium: Confronting simulations with the latest Lyman-alpha forest, Lyman-alpha emitter and CMB data

To illuminate the thermal and reionization history of the intergalactic medium (IGM), we confront cosmological hydrodynamical simulations that post-processed with radiative transfer codes and semi-numerical techniques with the latest data. Those data include observational constraints on the IGM temperature, the statistics of Lyman-alpha emitters and the opacity of the Lyman-alpha forest, as well as with the latest Planck measurements of the Thomson scattering optical depth. This enables us to derive improved constraints on the timing and sources of cosmic reionization. Furthermore, advances in the modelling of the cosmic UV background and the thermal evolution of the IGM will be discussed.

2017 Sep 21
14:30

Scott Gregory

(St Andrews)

The coronal genealogy of low-mass stars

Main sequence stars, like the Sun, follow a well defined rotation-activity relation with coronal activity increasing with increasing rotation rate until saturation is reached at log(LX/L*) ~ -3. Young, forming, low-mass stars do not follow this rotation-activity relation, with no link between X-ray emission and rotation rate for members of star-forming clusters. I will discuss the coronal evolution of low-mass stars over millions of years, and how and when the link between rotation and X-ray activity emerges.

2017 Sep 07
14:30

Federico Lelli

(ESO)

Structure and Dynamics of Nearby Galaxies

I will present recent results from the SPARC database: a sample of 175 late-type galaxies (spirals and irregulars) covering ~5 dex in luminosity and ~4 dex in surface brightness. Spitzer Photometry at 3.6 um provides the stellar mass distribution, while accurate HI/Halpha rotation curves trace the gravitational potential out to large radii. I will discuss several dynamical scaling laws, like the Baryonic Tully-Fisher Relation and the Radial Acceleration Relation. The latter relates the observed centripetal acceleration (gobs) to that expected from the baryonic distribution (gbar), implying a close link between baryons and dark matter in galaxies. The same relation is followed by ~2700 independent points at different radii in different galaxies. The observed scatter is remarkably small (30%) and largely driven by observational errors. Moreover, early-type galaxies and classical dwarf spheroidals seem to follow the same relation as late-type galaxies. This points to a "Natural Law" for galactic systems.

2017 Aug 03 14:30

Special Seminar: Max Gronke

(University of Oslo, Norway)

Towards a theoretical understanding of Lyman-alpha observables

Lyman-alpha (Lya) is the most prominent emission line in the Universe, and it provides a unique window into the high redshift Universe. In this non-technical talk, I will discuss some examples of how Lya observables can be used to study, for instance, the Epoch of Reionization, and the composition of the interstellar and circumgalactic medium.

To do this I will present some efforts on the modelling of the Lya luminosity function, and what we might learn from this regarding the escape of ionizing photons. Furthermore, I will give a brief introduction to Lya radiative transfer. This will include some more recent results which suggest that the `clumpiness' is a critical parameter influencing radiative transfer, and that the Lya spectrum is in fact sensitive to features on far smaller scales than other observational techniques. These results might explain a number of puzzling observations, including evidence for tiny-scale structure in the gas and the fact that the spectra are best fit by homogeneous models, despite our knowledge that the ISM and CGM are multiphase.

2017 July 27 14:30

Mark Miesch

(High Altitude Observatory)

Cycle Variability and Surface Flux Transport in a 3D Babcock-Leighton Solar Dynamo Model

Over the last two decades, Babcock-Leighton (BL) dynamo models have arguably emerged as the leading paradigm for explaining the origin of the 11-year solar activity cycle (22-year magnetic cycle). The defining characteristic of BL models is the critical role of magnetic flux emergence and dispersal in the operation of the dynamo. Emerging flux structures are manifested in the solar photosphere as bipolar magnetic regions (BMRs) with systematic orientations (known as Hale’s and Joy’s laws) that, upon further evolution due to differential rotation, meridional circulation, and convection, generate mean poloidal fields. We have recently developed an innovative solar dynamo model that captures this BL process explicitly in three dimensions. It’s called the Surface flux Transport And Babcock-LEighton (STABLE) solar dynamo model and it can be regarded as a unification of previous BL dynamo models (2.5D in latitude and radius) and surface flux transport (SFT) models (2D in latitude and longitude), building on the proven successes of each. Joy’s Law is the tendency for sunspot pairs (BMRs) to be tilted relative to the east-west direction with a tilt angle that systematically increases with latitude. All BL dynamo models rely on it, but few before STABLE have been able to explicitly capture departures from Joy’s law due to random scatter of BMR tilt angles, which is observed to be substantial. STABLE simulations suggest that the this tilt angle scatter may be sufficient to account for the observed variability in the amplitude of solar cycles. We find that tilt angle scatter can also induce extended periods of low activity known as Grand Minima. Furthermore, our model can usually recover from Grand Minima on its own, a feat that has eluded some previous BL models. I will also discuss the SFT aspects of STABLE, including convective flux transport, 3D poloidal field generation and the role of magnetic pumping.

2017 July 24 14:00

Special Seminar: Alexis P. Rouillard

(Institute of Research in Astrophysics and Planetology, Univeristy of Toulouse, France)

Modelling and data analysis support for Solar Orbiter and the future heliophysics observatory

2017 July 20
14:30

In Sung Jang

(AIP)

The tip of the red giant branch distances to type Ia supernova host galaxies and the Hubble constant

Modern methods of estimating the value of the Hubble constant are divided into two types: one is a classical method using the distance ladders including Type Ia supernovae (SNe Ia) based on the Cepheid calibration, and the other is based on the inverse ladder approach including cosmic microwave background  radiation (CMBR). Recently the values of the Hubble constant based on these two methods show a 2-3 sigma difference, which is called the Hubble tension. At the moment the causes for the Hubble tension are not yet known. To date the luminosity calibration of SNe Ia is mainly based on Cepheids, a well-known Population I candle, showing a sizable scatter.  The Tip of the Red Giant Branch (TRGB) is an accurate standard candle, but is a Population II distance indicator, having several advantages over Cepheids. An independent calibration of SNe Ia with the TRGB is needed for better calibration of SNe Ia and the corresponding value of the Hubble constant. In this talk, I will present my recent progress of the calibration of SNe Ia with the TRGB. Cosmological implications will be discussed.

2017 July 18 15:00

Special Seminar: Rolf Kuiper

(University of Tuebingen)

Recycling of Embedded Planets??? First Atmospheres

Context:
In the core accretion paradigm of planet formation, gas giants form a massive atmosphere in a run-away gas accretion phase once their progenitors exceed a threshold mass: the critical core mass. On the one hand, the majority of observed exo-planets, being smaller and rock/ice-dominated, never crossed this line. On the other hand, these exo-planets have accreted substantial amounts of gas from the circumstellar disk during their embedded formation epoch.

Methods:
We investigate the hydrodynamical and thermodynamical properties of proto-planetary atmospheres by direct numerical modeling of their formation epoch. Our studies cover one-dimensional (1D) spherically symmetric, two-dimensional (2D) axially symmetric, and three-dimensional (3D) hydrodynamical simulations with and without radiation transport. We check the feasibility of different numerical grid geometries (Cartesian vs. spherical), perform convergence studies, and scan the physical parameter space with respect to planet mass and optical depth of the surrounding.

Results:
In terms of hydrodynamic evolution, no clear boundary demarcates bound atmospheric gas from disk material in a 3D scenario in contrast to 1D and 2D computations. The atmospheres denote open systems where gas enters and leaves the Bondi sphere in both directions. In terms of thermodynamics, we compare the gravitational contraction of the forming atmospheres with its radiative cooling and advection of thermal energy, as well as the interplay of these processes. We find that the radiative cooling of atmospheric gas is counterbalanced by advection of atmospheric-disk gas, which prevents the proto-planets to undergo run-away gas accretion. Hence, this recycling scenario provides a natural explanation for the preponderance of super-Earth like planets.

2017 July 18 11:00

Special Seminar: Alice Quillen

(University of Rochester, USA)

Astro Visco-elastodynamics: Cracking moons and spin and obliquity evolution in tidally evolving and migrating satellite and planetary systems (II)

Close tidal encounters among large planetesimals and moons were more common than impacts. Using a mass spring model within an N-body simulation, we simulate the small deformation of a surface that is caused by a close tidal encounter.  We find tidal encounters can induce sufficient stress on the surface to cause large scale brittle failure of an icy crust.  Strong tidal encounters may be responsible for the formation of long graben complexes and chasmata in ancient terrain of icy moons such as Dione, Tethys, Ariel and Charon.

Mass spring models, originally developed for graphics and gaming applications, can measure remarkably small deformations and so can show tidal spin down of viscoelastic objects, directly tying simulated rheology to orbital drift and internal heat generation.  Inspired by the rapidly spinning Kuiper belt object Haumea, we go past analytical methods to measure how the tidal spin down rate depends on body shape and internal composition.

The new Horizons mission discovered that not only are Pluto and Charon’s minor satellites Styx, Nix, Kerberos, and Hydra, rapidly spinning, but surprisingly they have spin axis tilted into the orbital planet (they have high obliquities).   Long simulations of the minor satellites in a drifting Pluto-Charon binary system exhibit rich resonant spin dynamics, including spin-orbit resonance capture, tumbling resonance and spin-binary resonances.  With Charon drifting away from Pluto, Styx and Nix experience large swings in obliquity.  We propose that Styx and Nix’s currently high obliquities need not be primordial.  We attribute the tilting to a resonance between Styx or Nix’s spin precession rate, their orbit period and Charon’s orbit period.  The resonance differs from those explored previously accounting for Mars chaotic obliquity or Saturn’s current spin axis tilt.  By averaging the torque from a perturbing nearby mass (such as Charon), we construct a low dimensional dynamical model for the resonance that explains why it works on Styx and Nix.  We discuss possible application to Uranus and spin resonant processes that could take place in multiple exoplanet systems, with an eye toward being able to predict exoplanet spin and obliquity so as to inform exoplanet climate models.

2017 July 17
11:00

Special Seminar: Alice Quillen

(University of Rochester, USA)

Astro Visco-elastodynamics: Cracking moons and spin and obliquity evolution in tidally evolving and migrating satellite and planetary systems (I)

Close tidal encounters among large planetesimals and moons were more common than impacts. Using a mass spring model within an N-body simulation, we simulate the small deformation of a surface that is caused by a close tidal encounter.  We find tidal encounters can induce sufficient stress on the surface to cause large scale brittle failure of an icy crust.  Strong tidal encounters may be responsible for the formation of long graben complexes and chasmata in ancient terrain of icy moons such as Dione, Tethys, Ariel and Charon.

Mass spring models, originally developed for graphics and gaming applications, can measure remarkably small deformations and so can show tidal spin down of viscoelastic objects, directly tying simulated rheology to orbital drift and internal heat generation.  Inspired by the rapidly spinning Kuiper belt object Haumea, we go past analytical methods to measure how the tidal spin down rate depends on body shape and internal composition.

The new Horizons mission discovered that not only are Pluto and Charon’s minor satellites Styx, Nix, Kerberos, and Hydra, rapidly spinning, but surprisingly they have spin axis tilted into the orbital planet (they have high obliquities).   Long simulations of the minor satellites in a drifting Pluto-Charon binary system exhibit rich resonant spin dynamics, including spin-orbit resonance capture, tumbling resonance and spin-binary resonances.  With Charon drifting away from Pluto, Styx and Nix experience large swings in obliquity.  We propose that Styx and Nix’s currently high obliquities need not be primordial.  We attribute the tilting to a resonance between Styx or Nix’s spin precession rate, their orbit period and Charon’s orbit period.  The resonance differs from those explored previously accounting for Mars chaotic obliquity or Saturn’s current spin axis tilt.  By averaging the torque from a perturbing nearby mass (such as Charon), we construct a low dimensional dynamical model for the resonance that explains why it works on Styx and Nix.  We discuss possible application to Uranus and spin resonant processes that could take place in multiple exoplanet systems, with an eye toward being able to predict exoplanet spin and obliquity so as to inform exoplanet climate models.

2017 July 06 14:30

Smitha Subramanian

(KIAA, Beijing)

Mapping the Magellanic Clouds in 3D to trace their interaction history

The Magellanic system (located at a distance of ~ 55 kpc) which comprises of the Large Magellanic Cloud (LMC), the Small Magellanic Cloud (SMC), the connecting Magellanic Bridge (MB), the leading arms and the Magellanic Stream (MS), is one of the nearest examples of an interacting system in the local universe and an excellent template to study galaxy interactions using resolved stellar populations. Based on the revised proper motion estimates from the HST, it is more or less established that the evolution of the Magellanic system is mainly driven by the mutual interaction of the Magellanic Clouds. In this talk, I will present my work based on stellar populations (mainly red clump stars) to understand the 3D structure and interaction history of the Clouds.

2017 July 04
11:00

Special Seminar: Robin Kooistra

(Kapteyn Astronomical Institute, University of Groningen)

Detecting HI 21 cm emission from the IGM in large scale filaments with current and future radio telescopes

The cosmic web plays an important role in providing the environment for the formation and evolution of galaxies. Studying the role of local gas overdensities in the number density and general properties of galaxies requires  observations of the large scale IGM structure. However, cosmic web filaments have only been observed indirectly  through the positions of galaxies in large galaxy surveys or through absorption features in the spectra of high-redshift sources.

We propose to directly detect intergalactic medium filaments through their emission in the HI 21 cm line. This signal depends on the density in the filaments and the strength of the UV/X-ray background. We use high-resolution cosmological simulations to estimate the intensity of this emission in low-redshift filaments and use it to make predictions for the direct detectability of specific filaments previously inferred from galaxy surveys, in particular SDSS.

Given the expected signal of these filaments, our study shows that HI emission from large filaments can be observed by current and next-generation radio telescopes. We estimate that gas in filaments of length l >15 Mpc/h with relatively small inclinations to the line of sight (<10 deg) can be observed in ∼ 40–100 h with telescopes such as GMRT or EVLA. The large field of view allows upcoming instruments such as Apertif and ASKAP to detect large filaments independently of their orientation and curvature, which opens up the possibility of stacking the emission from multiple filaments. Furthermore, our estimates indicate that a more powerful future radio telescope like SKA can be used to completely map most of these filaments, which will allow them to be used as a strong cosmological probe.

2017 June 29 14:30

George Younis

(George Washington University)

The Strongest Magnets in the Universe

Magnetars represent the most extreme manifestation of the neutron star population. Their seconds-long rotational periods and large spindown rates imply surface dipole magnetic fields up to 7.0E14 G, the strongest ever measured in the Universe (million-billion times that of Earth), and young ages (thousands of years). They are detected mainly in our own Galaxy as bright X-ray emitters with luminosities exceeding their rotational energy losses. Magnetars are the most variable sources in the neutron star zoo on time-scales ranging from milliseconds to years. On milliseconds to seconds time-scale, they show a unique and peculiar bursting behavior of hard X-ray/soft gamma-ray radiation with luminosities reaching upward of 1.0E47 erg/s/cm2. Following these bursting episodes, magnetars enter a period of enhanced high energy radiation where their X-ray luminosities increase by as many as 3 orders of magnitude compared to their quiescent persistent emission. During this time, their rotational properties can show drastic changes either in the form of timing noise or glitches. They recover back to their usual self within months to years. In this talk, I will give an overview of the magnetar field through recent exciting discoveries such as the unexpected magnetar-like behavior of a rotation powered pulsar, the  discovery of the first wind nebula around a magnetar, a property normally associated to rotation powered pulsars, and the status of the strongest, most burst prolific of magnetars, SGR 1806-20, 13 and a half years after it emitted the brightest flash ever detected on Earth. Finally, I will conclude by looking at what the future holds for this rapidly growing field of research.

2017 June 28
15:30

Special Seminar: Jan-Torge Schindler

(University of Arizona)

The Extremely Luminous Quasar Survey (ELQS)

Studies of the most luminous quasars at high redshift directly probe the evolution of the most super-massive black holes in the early universe and their connection to massive galaxy formation. The Sloan Digital Sky Survey (SDSS) has so far provided the most widely adopted measurements of the quasar luminosity function (QLF) at z>3. However, a careful re-examination of the SDSS quasar sample revealed that the SDSS quasar selection is in fact missing a significant fraction of z>3 quasars at the brightest end.

Thus we designed the Extremely Luminous Quasar Survey (ELQS) to yield high completeness for bright (m_i < 18.0) quasars at z>2.8. In order to achieve this we have used a new near-infrared color selection complimented with machine learning methods for quasar classification and photometric redshift estimation.

I will present the novel selection technique along with the current results of the survey, which will be finished by the end of the year. All results indicate that a re-calculation of the bright end QLF is necessary as our survey roughly doubles the known SDSS quasars brighter than m_i < 17.5.

2017 June 15
14:30

Stefano Minardi

(AIP)

Integrated astrophotonics

Important discoveries in astronomy are often possible thanks to the progress of optical technologies. In the coming era of extremely large telescopes, photonic devices (i.e. devices manipulating light on scales comparable to its wavelength) are expected to play a central role in astronomical instrumentation, due to their potential for delivering compact, light-weight, and highly-multiplexed instruments with low maintenance needs.
In the Colloquium highlights from the research carried out by the ‘Integrated astrophotonics’ group at innoFSPEC/AIP will be presented, ranging from the development of compact photonic calibration sources for low- to high-resolution spectrographs, to applications of photonic lanterns, to multi-aperture spectro-interferometric devices.  We will discuss how these technologies could effectively contribute to enhance the performance of astronomical instruments enabling science cases ranging from exoplanetary and stellar astrophysics to cosmology. Concrete examples are represented e.g. by compact photonic calibration sources which could keep an accuracy in the order of a few cm/s over long periods (months or years) and high-precision, sparse aperture, intra-pupil spectro-interferometric instruments for the enhancement of the effective angular resolution of the telescope and the synthesis of high-contrast, spectrally-resolved images of astronomical targets.

2017 June 08 14:30

Karen Masters

(ICG, Portsmouth)

Constraints on Galaxy Evolution from Galaxy Morphology

The morphology of a galaxy provides information on the orbits of stars within it. As such, important clues to the formation history of galaxies is revealed by their morphologies, and this information is complimentary, but not identical to, their star formation history and chemical composition as revealed by photometry and spectra. The Galaxy Zoo project (www.galaxyzoo.org) has provided quantitative visual morphologies for over a million galaxies (including the entire Sloan Digital Sky Surveys, or SDSS Main Galaxy Sample), and has been part of a reinvigoration of interest in the morphologies of galaxies and what they reveal about the evolution of galaxies. Mapping Nearby Galaxies at Apache Point Observatory (MaNGA, part of SDSS-IV), is a new survey which aims to obtain spatially resolved spectral maps for 10,000 nearby galaxies (all of which have Galaxy Zoo morphologies). MaNGA began observations on the Sloan 2.5m Telescope in July 2014 and is already the largest sample of resolved spectroscopy in the world, with over 3200 galaxies observed. The first two years of MaNGA data will be publicly released via the SDSS interface in July 2017. In this talk I will review these projects, and show results from them which demonstrate why a resolved view of the internal morphology in galaxies is interesting and how it provides a unique constraint of our understanding of galaxy evolution.

2017 June 06 14:00

Special Seminar: Jay Gallagher

(Department of Astronomy, University of Wisconsin-Madison)

Exploring the Dark Hearts of Galaxies

The inner regions of disk galaxies not only contain various types of stellar bulges, but also frequently host dense molecular gas disks - central molecular zones (CMZs). CMZs are important astrophysical phenomena. They can contain a significant fraction of a galaxy's molecular gas in high density subsystems with widely varying star formation efficiencies. CMZs both obscure and potentially fuel AGN activity, while also providing the fuel for extreme starburst events. This talk will briefly review properties of CMZs in nearby, spiral galaxies, which offer a perspective on properties of normal CMZs. I will then discuss examples of extreme situations in which CMZs support starbursts or appear to be inert to star formation but are interacting with central supermassive black holes. Understanding the range of processes that can occur in CMZs thus holds a key to understanding the development of the dense cores of galaxies.

2017 June 02 14:00

Special Seminar: Timothy Davis

The dark hearts of galaxies: Molecules as dynamical probes of galaxy evolution

In this talk I will describe how mapping the dynamics of molecular clouds in the centre of galaxies can help us to constrain a wide range of astrophysical problems. From the enigmatic relation between galaxies and their supermassive black holes, the suppression of star-formation in dying galaxies, and the puzzling variation of the stellar initial mass function, molecules provide an ideal probe that can help us make progress. I will show how high resolution ALMA observations can be used to estimate the masses of supermassive black holes in galaxies across the Hubble sequence, and describe the WISDOM project, that aims to use this technique to constrain the importance of accreting SMBHs in galaxy quenching.  I will also show how one can use molecules to probe the controversial topic of variation in the stellar initial mass function.

 

2017 June 02
11:00

Special Seminar: Polychronis Papaderos

(Instituto de Astrofísica e Ciências do Espaço, CAUP, University of Porto)

FADO: a novel spectral population synthesis tool for the exploration of galaxy evolution by means of genetic optimization under self-consistency boundary conditions

Despite significant progress over the past decade, all current population spectral synthesis (PSS) codes suffer from two major deficiencies that limit their potential for gaining sharp insights into the star formation history (SFH) and chemical enrichment history (CEH) of star-forming (SF) galaxies, and potentially introduce substantial biases in studies of their physical properties (e.g., stellar mass, mass-weighted stellar age, specific SFR): i) the neglect of nebular continuum emission in spectral fits, consequently, ii) the lack of a mechanism that ensures consistency between the best-fitting SFH and the observed nebular emission characteristics (e.g., hydrogen Balmer-line luminosities and equivalent widths, shape of the continuum in the region around the Balmer and Paschen jump).

FADO (Fitting Analysis using Differential evolution Optimization; Gomes & Papaderos 2017, A&A, in press.; arXiv:1704.03922) is a conceptually novel, publicly available (www.spectralsynthesis.org) PSS code with the distinctive capability of permitting identification of the SFH and CEH that reproduce the observed nebular characteristics of a SF galaxy. This so far unique self-consistency concept allows us to significantly alleviate degeneracies in spectral synthesis, thereby opening a new avenue to the exploration of the assembly history of galaxies. FADO is the first PSS code employing genetic Differential Evolution Optimization. This, in conjunction with various other elements in its mathematical concept and numerical realization, results in key improvements with respect to computational efficiency and uniqueness of the best-fitting SFHs.

2017 May 24
14:00

Special Seminar: Robin Shelton

(University of Georgia USA)

High Velocity Clouds of Gas Traveling into and through Galaxies

Astronomical observations have found enormous and fast-moving gas clouds near the Milky Way Galaxy and near other large spiral galaxies.  Some are near the rarefied outskirts of their host galaxy, while others are poised to collide with the disk.  With speeds in excess of 100 km/sec and masses that can easily exceed a million solar masses, they can bring both distruptive power and fresh material to a galaxy.    My group has been computationally modeling these fast-moving clouds, called high velocity clouds (HVCs).  In various simulations, we consider the effects of dark matter,  magnetic fields, and non collisional ionizational equilibrium of the metal atoms.   Our goal is determine how HVCs interact with galaxies.   In this presentation, I will show how HVCs evolve on timescales of hundreds of millions of years as they travel through the circumgalactic and halo regions and through galactic disks, and how they seed the halo with warm gas, condense and capture halo material, and punch holes in the galactic disk.

2017 May 18 14:30

10th AIP Jamboree

Who does what

The tenth round of speakers:

Xanthippi Alexoudi, Cameron Bell, Olga Bellido Tirado,
Frank Breitling, Ismael Enrique Carrillo Rivas, Cristina Chiappini,
Omar Choudhury, Carsten Denker, Arianna Di Cintio,
Igor Di Varano, Andrea Diercke, Dalal El Youssoufi,
Detlef Elstner, Janine Fohlmeister, Yori Fourni,
Steffen Frey, Dario Fritzewski
2017 May 17 11:00

Gongbo Zhao

(NAOC, China)

Understanding the cosmic acceleration using large scale structure surveys

The origin of the cosmic acceleration has been one of the key problems to solve in modern sciences. According to what we know so far, it might be due to the effect of dark energy, or to our misunderstanding of gravity. In this talk, I will explore the possibilities and practicalities of tackling this challenging cosmic acceleration problem using large scale structure surveys including BOSS, eBOSS and DESI. I will also address the issue of tension among different kinds of recent astronomical observations, and offer a solution to release the tension using the dynamical dark energy.
2017 May 16
16:00

Special Seminar: Timur Doumler

(AIP)

Life after astronomy

A PhD in Astronomy may seem to some as a narrow and highly specialised degree. Of course in some ways it is, however in many ways the skills acquired during a PhD can be transferred to a variety of other industries. In my PhD, I was working on numerical simulation techniques and after graduating from the AIP pursued a career as a software developer, working at different tech companies in Germany and the UK. The jump from astrophysics PhD student to professional software engineer was at times exciting and intimidating, challenging and rewarding. In my talk I’ll explain a little bit about my experience leaving academia - what to look forward to in a world outside of academic research, the challenges my training prepared me for and the hurdles I found more difficult to overcome. I'll explain a little bit about my current work and, having now been on both sides of the job interview table, a little bit about what potential employers like and dislike in a candidate that comes directly out of research.

2017 May 16 14:00

Special Seminar: Philipp Gast

(AIP)

Formation of dense gas cores due to supernova remnant-cloud interactions

2017 May 16
11:00

Special Seminar: Sebastian Sanchez

From Global to Local properties in galaxies

The way we characterize galaxies and study their evolution in the last two decades, in an statistical way, is to derive integrated, average or characteristic properties and explore the possible relations between them. Those relations are latter interpreted in the frame of scenarios about their cosmological evolution. However, that approach misses the fundamental point that galaxies are resolved entities which evolution may be governed by local rather than global processes. In this talk we explore three different well know global relations that are the reflection of local ones: (i) The star-formation Main Sequence, (ii) The mass metallicity relation and (iii) the Age bimodality. That perspective opens a new view on how galaxies should be studied and understood.

2017 May 11 14:30

Jochen Liske

(Hamburg)

The low-redshift universe as seen by the Galaxy And Mass Assembly survey

Large galaxy surveys have been a driving force in developing our understanding of galaxy evolution for more than two decades. Their role is to systematically characterise galaxies as a function of key parameters and to disentangle the complex interplay between dark matter, stars, gas, dust and AGN. While much of the action in galaxy evolution happens at redshifts > 1, the value of low-redshift surveys lies in the comprehensiveness and statistical power with which they are able to describe the end product of galaxy evolution. In this talk I will review a selection of results from the recently completed Galaxy And Mass Assembly survey. GAMA combines an extensive spectroscopic survey with imaging data from seven ground-based facilities and four space missions in order to construct a unique multi-wavelength data set covering all major galaxy constituents. I will discuss results concerning the galaxy stellar mass function, the halo masses and mass-to-light ratios of galaxies and groups, the star formation rate and the build-up of stellar mass through mergers.

2017 May 04
14:30

Alessandra Buonanno

(Albert Einstein Institute, Potsdam)

The New Era of Precision Gravitational-Wave Astrophysics

The LIGO detection of gravitational waves emitted by coalescing binary black holes heralded a new era in physics and astrophysics. In this talk, I will first review the theoretical groundwork that allowed to identify and interpret the gravitational-wave signals, and carry out tests of general relativity in the strong-field, highly dynamical regime. I will then highlight the unique science that lies ahead of us with upcoming gravitational-wave observations, including gravitational signals from binary neutron stars, and discuss the theoretical challenges in solving the two-body problem in gravity that we need to address if we want to take full advantage of the discovery potential.

2017 Apr 25
14:00

Special Seminar: Alexei Pevtsov

(National Solar Observatory, USA and University of Oulu, Finland)

“Old” data – new science or why do we need long-term synoptic programs

It is not uncommon to see the references to recent (cycle 24) solar activity as “exceptionally low” or as an “extended long-term decline”. But how would we know that the current level of activity is unusual if we did not have historical data taken over many cycles? How would we know, for example, what are the strongest field strengths in sunspots and how they change with time or that the amplitude of next cycle could be defined by the strength of polar field in previous cycle if we did not have long-term records of solar activity? Truly, synoptic observations feed future research to solve issues that may not be identified at the time when data are acquired. In my talk, I will discuss the current state of long-term synoptic programs and present results of my recent projects on reconstructing the solar activity using historical data.

2017 Apr 20
14:30

Volker Bromm

(University of Texas at Austin)

The First Stars and Galaxies: Countdown to the JWST

How did the formation of the first stars and galaxies end the cosmic dark ages, a few hundred million years after the Big Bang? I will review our emerging theoretical framework of this fundamental cosmic transformation, taking stock of what we know, just ahead of the JWST launch. How do the first supernovae enrich the pristine intergalactic medium, and how does the energetic feedback from stars and black holes shape the assembly process of the first galaxies? I will discuss strategies to probe our theoretical ideas, both with frontier observations at high redshifts, and with surveys of local metal-poor stars ("stellar archaeology").

2017 Apr 19
11:00

Special Seminar: Vardha Bennert

(Cal Poly - San Luis Obispo)

The Origin of the Black Hole Mass Scaling Relations

The discovery of close correlations between supermassive BHs and their host-galaxy properties has sparked a flood of observational studies pertaining both to the local Universe and cosmic history over the last decade. Nevertheless, a clear understanding of their origin still eludes us. Uncertainty remains as to the fundamental driver of these relations, whether purely local and baryonic or global and dark matter dominated. While studying the evolution of these relations with cosmic time provides valuable clues, a definitive resolution of this conundrum relies on understanding slope and scatter of local relations for AGNs. We discuss results from a unique three-fold approach. (i) From a sample of ~100 AGNs in the local Universe, we build a robust baseline of the BH mass scaling relations (MBH-sigma, MBH-L, MBH-M), combining spatially-resolved Keck spectroscopy with SDSS imaging. (ii) We study the evolution of the MBH-sigma and MBH-L relations out to a look-back time of 4-6 Gyrs using Keck spectra and HST images. (iii) We extend this study out to the pivotal cosmic time between the peak of AGN activity and the establishment of the present-day Hubble sequence, a look-back time of 8-10 Gyrs. We measure spheroid stellar masses using deep multi-color HST images from GOODS and determine the MBH-M relation. The results (i) indicate that AGNs follow the same scaling relations as inactive galaxies. From (ii-iii) we conclude that BH growth precedes bulge assembly. Combining results from (i-iii) allows us to test the hypothesis that evolution is driven by disks being transformed into bulges.

2017 Apr 18
14:00

Special Seminar: Jake D. Turner

(University of Virginia)

The search for radio emission from exoplanets using LOFAR low-frequency beam-formed observations

Detection of radio emission from exoplanets can provide information on the star-planet system that is very difficult or impossible to study otherwise, such as the planet’s magnetic field, magnetosphere, rotation period, orbit inclination, and any star-planet interactions. Such a detection in the radio domain would open up a whole new field in the study of exoplanets, however, currently there are no confirmed detections of an exoplanet at radio frequencies. In this talk, we discuss our ongoing observational campaign searching for exoplanetary radio emissions using beam-formed observations within the Low Band of the Low-Frequency Array (LOFAR). To date we have observed three exoplanets: 55 Cnc, Upsilon Andromedae, and Tau Boötis. These planets were selected according to theoretical predictions, which indicated them as among the best candidates for an observation. During the observations we usually recorded three beams simultaneously, one on the exoplanet and two on patches of nearby “empty” sky. An automatic pipeline was created to automatically find RFI, calibrate the data due to instrumental effects, and to search for emission in the exoplanet beam. Additionally, we observed Jupiter with LOFAR with the same exact observational setup as the exoplanet observations. The main goals of the Jupiter observations are to train the detection algorithm and to calculate upper limits in the case of a non-detection. Preliminary results on the detection of radio emission from 55 Cnc will be discussed but data analysis is currently ongoing for the full set of data.

2017 Apr 13
14:30

Mirko Krumpe

(AIP)

Clustering measurements of Active Galactic Nuclei

In the last decade, large area surveys (e.g., SDSS, 2dF, XMM-COSMOS) have significantly improved AGN clustering measurements. The analysis of clustering studies now provide tight constraints on the environment in which super-massive black hole accretion takes place. In my talk, I will give an elaborate and easy-to-follow introduction on what clustering measurements are and how they are performed. I will explain how we are able to measure AGN clustering at low redshift with an unprecedented precision and how we interpret these results. The results of a series of published papers on broad-line AGN clustering will be presented. Finally, I will conclude by giving an outlook of which data sets will be available for AGN clustering studies in the future.

2017 Apr 06
15:30

Carlos Frenk

(ICC, Durham)

A conclusive test of cold dark matter

The ``Lambda cold dark matter'' (LCDM) cosmological model is one of the great achievements in Physics of the past thirty years. Theoretical predictions formulated in the 1980s turned out to agree remarkably well with measurements, performed decades later, of the galaxy distribution and the temperature structure of the microwave background radiation. Yet, these successes do not inform us directly about the nature of the dark matter. Indeed, there are competing (and controversial) claims that the dark matter might have already been discovered, either through the annihilation of cold, or the decay of warm, dark matter particles. In astrophysics the identity of the dark matter manifests itself clearly in the properties of dwarf galaxies, such as the satellites of the Milky Way. I will discuss predictions from cosmological simulations assuming cold and warm (in the form of sterile neutrinos) dark matter.

2017 Apr 05
14:00

Special Seminar: Frederick Gent

(Aalto University Finland)

Supernova driven turbulence: Magnetic field and multiphase structure of the interstellar medium

Using direct numerical simulations of the interstellar medium (ISM) stirred and heated by supernova explosions in rotating disk galaxies, we investigate its thermal structure. The model is the first to invoke a dynamo, which includes large scale and small scale dynamo in the ISM, which advances investigation of how the magnetic field is generated in disk galaxies and how the features of the magnetic field interact with the multiphase structure of the ISM. We consider local averaging techniques, as an alternative to horizontal averages, to understand the separation of scales in the magnetic field, velocity field, etc. over arbitrary domains.

2017 Mar 30
14:30

Svetlana Berdyugina

(KIS, Freiburg)

A quest for extraterrestrial life using polarimetry and high-dynamic range telescopes

Polarimetry of exoplanets opens exciting opportunities to investigate their atmosphere composition and thermodynamics. We continuously improve sensitivity of our instruments and approach the level required for detection of Earth-like exoplanets. If atmospheres of these planets are optically thin like on Earth, we will be able to investigate their surface composition and search for both atmospheric and surface biosignatures. Now we undertake a comprehensive laboratory and theoretical studies to establish remote-sensing tools which can unambiguously detect extraterrestrial life. In this talk I will present our recent study of photosynthetic organisms in polarized light and modeling exo-Earth polarized spectra with atmospheric and biopigment signatures. I will demonstrate how variations in the planet surface composition affects polarized spectra and which sensitivity is required to detect such variations. In particular, we aim to investigate the recently discovered nearest possible Earth-like planet Proxima b using our remote-sensing tools. However, even this nearby planet requires telescopes with the aperture larger than 10m and significant improvements in suppressing scattered stellar light background well below the current best effort of one part per million at angular separations of a few wavelength-to-diameter ratio. I will present recently proposed novel concepts of interferometric telescopes with the effective aperture larger than 20m which can achieve such high dynamic range and provide first views of nearby exoplanets and provide the first census of nearby potentially habitable exoplanets.

2017 Mar 29
11:00

Special Seminar: Aleksandr Mosenkov

(Ghent University Belgium)

Structural properties of edge-on galaxies

I will briefly review main structural properties of edge-on galaxies which can be derived via photometric decomposition analysis and radiative transfer modeling of galaxies. I use observations in a wide domain of wavelengths (from UV to far-infrared and submm wavelengths) in which stellar and dust properties can be broadly studied. I consider edge-on galaxies of different morphology: from early to late-type spirals, including peculiar galaxies with polar rings and polar bulges and galaxies with different structural features (disc warps and truncations, LSB details, boxy/peanut-shape bulges and galaxies with very thin discs). The new software pipeline DECA for performing automated and manual decompositions and estimating structural parameters of galaxies has been designed and used in this study. DECA provides new capabilities to investigate large samples of galaxies and obtain their general structural characteristics as well as to carry out a detailed analysis of various galaxy features. I will discuss some famous galaxy scaling relations with an attempt to link them to galaxy formation and evolution.

2017 Mar 28
16:00

Special Seminar: Maksym Tsizh

(Ivan Franko Natiaonal University of Lviv, Ukraine)

Cosmic voids as a probe of dark energy

In my talk i will tell you about our research of evolutionof cosmological perturbations which leads to the formation of largeisolated voids in the Universe. We assume that initial perturbationsare spherical and all components of the Universe (radiation, matterand dark energy) are continuous media with perfect fluidenergy--momentum tensors, which interact only gravitationally.Negative density perturbations with the initial radius about 50 Mpc incomoving to the cosmological background coordinates and the amplitudecorresponding to the r.m.s. temperature fluctuations of the cosmicmicrowave background lead to the formation of voids with the densitycontrast up to -0.9, maximal peculiar velocity about 400 km/s and theradius close to the initial one.

Equations of the evolution of perturbations for every component in thecomoving to cosmological background reference frame are obtained fromequations of energy and momentum conservation and Einstein's ones and are integrated numerically. Initial conditions are set at the early stage of evolution in the radiation-dominated epoch, when the scale of perturbation is much larger than the particle horizon. Results show how the profiles of density and velocity of matter and dark energy are formed and how they depend on parameters of dark energy and initial conditions. In particular, we have found that final matter density and velocity amplitudes change within range 4-7\% when the value of equation-of-state parameter of dark energy w vary in the range from 0.8 to 1.2, and change within 1\% only when the value of effective sound speed of dark energy vary over all allowable range of its values.

We have also shown that ratio of the peculiar velocity in units of the Hubble flow to the density contrast in the central part of void does not depend or depends weakly on the distance from center of the void. However, this ratio is sensitive to the values of dark energy parameters and can be used for finding them on basis of the observational data on mass density and peculiar velocities of galaxies in the voids.

2017 Mar 23
14:30

Philipp Richter

(Uni Potsdam)

The circumgalactic gaseous environment of the Milky Way and other low-redshift galaxies

The Milky Way is surrounded by large amounts of diffuse gaseous matter that connects the stellar body of our Galaxy with its large-scale Local Group environment. To characterize the absorption properties of this circumgalactic medium (CGM) we have constructed the so-far largest survey of ultraviolet absorption features of the Milky Way CGM, based on the analysis of several hundred HST/COS spectra. In this talk I will present the main results of this survey and discuss the spatial distribution of the gas and its physical properties in the context of the evolution of the Milky Way and other Local Group members. In addition, I will provide a comparison between the Milky-Way CGM and circumgalactic gas around other low-redshift galaxies.

2017 Mar 09
14:30

Kevin Schawinski

(ETH, Zürich)

Supermassive black holes: from deep fields to deep minds

How the massive black holes in the centers of most galaxies first formed, grew, and interacted with their host galaxies are among the key outstanding questions in astrophysics. I will outline how the latest ground and space telescopes get us closer to the first black hole seeds and discuss a new framework for how the galaxy-black hole system as a whole operates. Building on the last decade of discovery in galaxy evolution, we are now able to ask the right questions that will ultimately lead us to the physics of how growing black holes - quasars - regulate and shut down the star formation in galaxies. I will outline how current and near-future facilities will answer these questions, and briefly touch how ongoing developments in machine learning can help us take astronomy to the next level.

 

2017 Feb 27
14:00

Special Seminar: Travis Metcalfe

(Space Science Institute, Boulder, USA)

The rotation and magnetic activity of Kepler field stars

Precise photometry from the Kepler space telescope allows not only the measurement of rotation in solar-type field stars, but also the determination of reliable masses and ages from asteroseismology. These critical data have recently provided the first opportunity to calibrate rotation-age relations for stars older than the Sun. The evolutionary picture that emerges is surprising: beyond middle-age the efficiency of magnetic braking is dramatically reduced, implying a fundamental change in angular momentum loss beyond a critical Rossby number (Ro~2). We have compiled chromospheric activity measurements for the sample of Kepler asteroseismic targets that were used to establish the new rotation-age relations. We use these data along with a sample of well-characterized solar analogs from the Mount Wilson HK survey to develop a qualitative scenario connecting the evolution of chromospheric activity to a fundamental shift in the character of differential rotation. We conclude that the Sun may be in a transitional evolutionary phase, and that its magnetic cycle might represent a special case of stellar dynamo theory.

2017 Feb 16
14:30

Special Seminar: Meetu Verma

(AIP)

Multi-wavelength observations of the solar active regions: formation and decay

The accurate measurement of magnetic and velocity fields in and around solar magnetic features is the key to unlocking the mysteries surrounding their formation and decay. High-resolution spectra and image sequences from the 1.5-meter solar telescope GREGOR give us an opportunity to look into 3-D flow fields in and around solar features. I present two case studies detailing observations of two evolutionary stages of solar active regions, i.e., (1) an emerging flux region and (2) the decay of sunspot penumbra. In addition, I will summarize the coordinated observing campaign carried for the latter case study. The results and findings from high-resolution observations will be discuss in the context of data from the space mission Solar Dynamics Observatory (SDO).

2017 Feb 02
14:30

Chris Brook

(IAC, Tenerife)

Abundance Matching in the Local Volume

I will explain Abundance Matching, a process that links the stellar or baryonic mass of galaxies to the mass of dark matter halos. I will highlight the importance of extending this relation to low mass galaxies, in relation to resolving the small scale problems of the cold dark matter paradigm, i.e. the "missing satellite", "too big to fail" and "cusp-core" problems. I will also highlight the difficulties in deriving the relation at low masses, including completeness limits of observations, small number statistics, and the effects of scatter in the relation. These difficulties will be improved by current surveys of larger local volumes that promise to be complete to relatively low stellar masses.

2017 Jan 25
11:00

Special Seminar: Reza Moetazedian

(Heidelberg)

Importance of satellites infall on the Milky Way disc's dynamics

Within the framework of this study, we use high-resolution N-body simulations in order to examine the impact of infalling satellite galaxies with satellite-to-disc mass ratios > 0.003, on to our Milky Way thin disc with the aim of explaining the contribution of minor mergers to the total observed vertical heating of the Galactic thin disc in the solar neighbourhood. The initial conditions(ICs) of satellites originate from a set of 7 Milky Way-like cosmological simulations, including Via Lactea II and the Aquarius. Our results benefit from the capability of resolving the dynamics of the disc down to 40 parsecs. In addition, we take advantage of an isolated multi-component MW galaxy in much better equilibrium state, in comparison to previous attempts. I would also like to present our work on the relevance of satellite interaction to the time of bar formation in Milky Way-like galaxies. If time allows, I would discuss my most recent work concerning the signatures of radially oscillatory behaviour in the outer disc part due to the infall of a Sagittarius-mass satellite in Aq-F2 simulation. Observed features such as Monoceros ring are also observed in our simulations, supporting the theory of such infall being responsible for the observed features.

2017 Jan 25 10:00

Special Seminar: Rebecca McElroy

(The University of Sydney)

Investigating the host galaxies of luminous AGN in the local universe with integral field spectroscopy

This talk demonstrates that outflows are ubiquitous among luminous local type 2 AGN using observations from the AAT's SPIRAL instrument. Using multiple component Gaussian emission line decomposition we are able to disentangle the kinematic and ionisation properties of these winds. This allows us to argue that the outflows from these AGN are directly impacting the surrounding ISM within the galaxies.

I will also highlight the discovery of an AGN that has changed spectral type not once, but twice. So called âEUR˜changing lookâEUR(tm) AGN are an uncommon phenomenon, but twice changed AGN are much rarer. This AGN first transitioned from a narrow line AGN (type 2) to a broad line AGN (type 1) in the 1980s. It was recently observed as part of The Close AGN Reference Survey (CARS). Examination of the MUSE data for this particular source showed that it no longer had the spectral features typical of a type 1 AGN. The continuum emission from the accretion disk was no longer visible and the broad lines were dramatically diminished. In this talk we describe the possible reasons for this change, supported by analysis of multi-epoch optical photometry and spectroscopy, alongside data obtained through directorâEUR(tm)s discretionary time from Chandra, HST, and the VLA. We then conclude by discussing the implications of this discovery on our understanding of AGN timescales and the physics behind AGN spectral types.

Finally I will highlight my current work on stellar kinematics on the CARS sample, and how we can use this to investigate the formation histories of these galaxies.

2017 Jan 19
14:30

Adriana Mancini Pires

(AIP)

The missing links of neutron star evolution in the eROSITA era

Since the discovery of the first radio pulsar fifty years ago, the population of neutron stars in our Galaxy has grown to over 2500, of which a handful is exclusively seen in X-rays. Despite their scarcity, these sources are key to understanding aspects of neutron star phenomenology and evolution not observed in the normal pulsar population. The forthcoming all-sky X-ray survey of eROSITA is timely for a better sampling of neutron stars that are especially silent in the radio and gamma-ray regimes. In this talk I will review how alternative evolutionary scenarios (in particular, involving magnetic field decay and fallback accretion) can explain the neutron star diversity and visibility across the electromagnetic spectrum; I will also discuss the expected role of eROSITA - and the challenges it will face - at probing the population as a whole.

2017 Jan 12
14:30

Aline Vidotto

(Trinity College Dublin)

Stellar magnetic activity and their effects on planets (and vice-versa)

In this talk I will review some recent works on the magnetic activity of Sun-like stars, their winds and potential impact on surrounding exoplanets. Stellar magnetic fields drive space weather on (exo)planets, being responsible for the ejection of stellar winds and bursty events, such as flares and coronal mass ejections. The dramatic differences in the Physical properties of the host stars compared to the properties of our Sun, in addition to the extreme architecture of most of the known exoplanetary systems, can give rise to physical interactions that might not even be recognised in the solar system. These interactions can generate observable signatures, thus providing other avenues for exoplanet detection and assessing exoplanetary properties, which would otherwise remain unknown.

2017 Jan 11 14:00

Special Seminar: Carolina von Essen

(SAC at Aarhus University, Denmark)

Looking deeper into exoplanet atmospheres: improved model for transmission spectroscopy owed to high resolution spectroscopy

Exoplanet transit events offer the opportunity to characterize the atmospheres of extrasolar planets by transmission spectroscopy. During a transit, a fraction of the star light shines through the outmost layers of the planetary atmosphere, picking up a spectral fingerprint of the planetary atmosphere.

Currently, models used to characterize the atmosphere ignore several fundamental effects: The changes of stellar absorption lines with limb darkening, (ii) the orbital movement and the resulting radial velocity changes, and (iii) the potential rotation of the planetary atmosphere. All these effects are fundamental to correctly determine chemical abundances.

After a broad introduction about transmission spectroscopy, I will show you the work I have done to model these effects, and how we have detected them in the atmosphere of HD-189733b using ESO/UVES. I will end up stressing how such measurements can help us estimate chemical abundances and, in some cases, even orbital configurations.

2016
2016 Dec 21
15:30

Special Seminar: Alexander Kolodzig

(Kavli Institute, Beijing)

Can AGN, galaxy clusters, and WHIM explain the surface brightness fluctuations of the cosmic X-ray background?

Studies of the surface brightness fluctuations of the cosmic X-ray background (CXB) are becoming a new frontier of large-scale structure (LSS) studies in X-rays. Those fluctuations carry unique information about faint and low luminosity source populations, which are inaccessible for conventional LSS studies based on resolved sources. I will demonstrate this by presenting the first full description of CXB fluctuations on the angular scales up to ~3deg. It is the result of our extensive study of the CXB fluctuations with XBOOTES, which is currently the largest continuous extragalactic survey by Chandra covering an area of ~9deg^2. It enabled us to conduct the most accurate measurement of power spectrum of CXB fluctuations to date.

2016 Dec 15
14:30

Tim Beers

(University of Notre Dame)

Carbon in the Early Universe and Observational Constraints on First-Star Nucleosynthesis

Over the past 25 years, it has been recognized that the light element carbon plays a crucial role in the early chemical enrichment of the Universe. One fundamental observation is that the frequency of the so-called carbon-enhanced metal-poor (CEMP) stars in the Milky Way increases dramatically with decreasing iron abundance – from 20% of all stars with [Fe/H] < -2.0 to > 80% of stars with [Fe/H] < -4.0. Recent discoveries of enhanced carbon in damped Lyman alpha systems at high redshift reveal that the abundance patterns observed in this gas are commensurate with a sub-class of the CEMP stars, the so-called CEMP-no stars, which exhibit little or no enhancement of their neutron-capture elements – providing one of the first direct observational linkages between the high-z Universe and presently observed stars in the Galaxy. I summarize recent progress on our understanding of the production of carbon by first-generation stars, and the powerful constraints that this information provides on Galactic chemical evolution models, the initial mass function in the early Universe, and the nature of first-star nucleosynthesis.

2016 Dec 14
10:00

Special Seminar: Claudia Reinlein

(Fraunhofer Institute Jena)

Active and Adaptive Optics at the Fraunhofer IOF

Active and Adaptive Optics is more and more used in ground-based telescopes and also in discussion for space telescopes. For both types of systems there are completely different technological requirements. While space telescopes mainly aim for active optics, ground-based systems apply both active and adaptive optics.

This talk describes the technological features and the state of the art of "deformable mirrors / AO systems". And here the focus will be set onto research and development projects of the Fraunhofer IOF (Jena).

In the framework of an ESA project, a test breadboard is developed, in order to demonstrate the capability to compensate for static aberrations in using active mirrors in space telescopes. In the future, telescopes with a diameter of 4-16m will be used for the search for extraterrestrial life. In this context, IOF develops and investigates an active mirror with "set-and-forget" characteristics to compensate for aberrations conditional of manufacture and assembly.

For the European Extremely Large Telescope (E-ELT) a technology development for extreme AO (X-AO) is conducted. In this context, the talk will inform about a technological pre-investigation (design) of a deformable mirror with 11000 actuators.

For laser communication between a ground-station and a geostationary satellite, the pre-compensation of aberrations is a technique to increase the signal intensity at the receiver and to attenuate disturbing speckles. The talk will also present the real-time AO of the Fraunhofer IOF and its compensatory efficiency as a function of the correction angle.

2016 Dec 13
14:00

Special Seminar: Marco Potenza and Mirko Siano

(University of Milano)

Wavefront characterization of partially coherent light

Wavefront characterization is of fundamental importance in many applications and research areas, e.g coherent and incoherent imaging, phase-sensitive techniques, optics metrology, beam diagnostics. In the first part of this seminar we show how to probe wavefront phase correlations (coherence properties) of radiation beams in third and fourth-generation light sources with the Heterodyne Near Field Speckle method. Experimental results obtained with undulator radiation at ESRF, SASE FEL at SPARC_LAB and synchrotron radiation at ALBA are provided. We also introduce the novel Asymmetric Lateral Coherence approach, which exploits many asymmetric Young’s interferometers to retrieve spatial features of broadband sources. In the second part of this seminar we address the problem of wavefront phase sensing and reconstruction. We focus on vortex beams, i.e. light carrying Orbital Angular Momentum, describing their generation and the current diagnostics to evidence the phase helicity.

 

2016 Dec 13
13:00

Special Seminar: Marco Potenza and Mirko Siano

From light scattering to hyperspectral imaging: optical analogical simulations

Light scattering is ubiquitous, both in Nature and applications. I will report about the results obtained in the recent years exploiting the fundamentals of light scattering to the study, characterization and applications of nano- and micro-particles.

2016 Dec 13
11:00

Special Seminar: Sabyasachi Chattopadhyay

(IUCAA, Pune, India)

DOTIFS - a multi-deployable fibre-fed IFU Spectrograph

Devasthal Optical Telescope Integral Field Spectrograph (DOTIFS) is a new multi-object integral field spectrograph being built by the Inter-University Centre for Astronomy and Astrophysics (IUCAA), Pune, India for the 3.6m Devasthal Optical Telescope, (DOT). The Devasthal Observatory has been constructed by the Aryabhatta Research Institute of Observational Sciences (ARIES), Nainital. DOTIFS is mainly designed to study the physics and kinematics of ionized gas, star formation and H II regions in the nearby galaxies. DOTIFS is a novel instrument in terms of multi-IFUs, built in deployment system, and high throughput. A magnifier at the Cassegrain side port of the telescope feeds sixteen integral field units (IFUs). The IFUs can be deployed over an 8’ diameter focal plane by x-y actuators. An intelligent deployment algorithm has been developed to allow optimized reconfiguration and to avoid any collision between IFUs. The whole deployment system has a complex 3-dimensional structure to allow maximum positioning freedom to the IFUs. The speaker will provide details of the instruments and the challenges. The instrument is at the phase of fabrication and is scheduled to be commissioned in late 2017.

2016 Dec 08
14:30

Cameron Bell

(AIP)

A revised age scale for young Galactic clusters

The formation and evolution of low-mass stars and planets is one of the fundamental goals of modern astronomy, however our understanding hinges upon the ability to assign precise and reliable ages to young stars. Unfortunately, the age of a star is not a directly measurable property and thus the ages of all young stars are "to varying degrees" model-dependent, and it is this dependency which can result in uncertainties of up to 100% depending on which age-dating technique one adopts and over which mass range it is applied.

In this talk I will give a brief overview of several methods of age-dating young stars, however I will place a large emphasis on the most common of these; namely the use of model isochrones. I will discuss the underlying issues with these methods before introducing a set of semi-empirical model isochrones incorporating an empirical colour-Teff relation and bolometric corrections based on the observed colours of Pleiades members, with theoretical corrections for the dependence on log g. Using these models I will present a revised age scale for young Galactic clusters and associations in the Solar Neighbourhood for which the pre-main-sequence contraction and main-sequence turn-off and lithium depletion boundary ages agree. This revised age scale implies that the canonical ages for young (< 15 Myr) clusters are likely too young by a factor of two; a result with wide-ranging implications.

2016 Dec 02 11:00

Special Seminar: Elena D'Onghia

(University of Wisconsin, Madison)

The Origin and Fate of the Magellanic Stream

The Magellanic Clouds are surrounded by an extended tail of neutral and ionized gas, known as the Magellanic Stream, trailing the Clouds in their orbit around the Milky Way. The complexity of the Stream's morphology, spatial extent and metallicity present a challenge to current numerical simulations. Current simulations for the formation of the Stream show that tidal forces acting between the Clouds are suffi^Ncient to strip material when the Clouds are at their first pericentric passage around the Milky Way.

I will show that several major di^Nfficulties are experienced in the first-passage scenario, that call for additional physics and a multiple passage of the Clouds around the Milky Way: 1) the observed Stream of gas is signicantly more extended on the sky than the simulated Stream; 2) the position of the Leading Arm is inconsistent with its observed location. I will show HI data that indicate additional evidence of a previous passage of the Clouds in the Milky Way and show some preliminary numerical simulations that provide an alternative scenario for the formation of the Stream.

2016 Nov 30
14:30

Elena D'Onghia

(University of Wisconsin, Madison)

The Structure and Dynamics of the Milky Way Stellar Disk

Ongoing surveys are revolutionizing our understanding of Galaxy dynamics. At the same time, advances in computational cosmology have led to improved predictions for the properties of galaxies in the LCDM theory. This simultaneous progress has transformed the field of the dynamics of the Milky Way and its dwarf galaxies into a powerful testing ground for both cosmological and galaxy formation theories. One important result of the last decades is that cosmological simulations of the Milky Way overpredict by a large factor the number of dwarf satellite galaxies orbiting our Galaxy. I will present numerical experiments illustrating how this population of dark and visible satellites may affect the structure of the stellar disk. I will also discuss how a satellite as massive as the Sagittarius dwarf galaxy passing through the disk excites coupled stellar motions in the solar neighborhood, leading to coherent vertical oscillations of the disk. These findings have implications for the local disk density estimate, and the amount of dark matter at the Sun's location. I will argue that, even in the JWST era, the study of the Milky Way may be our best probe of physical processes driving the formation and evolution of spiral galaxies.

2016 Nov 30
11:00

Special Seminar: Chervin Laporte

(Columbia University)

The response of the Milky Way to the Large Magellanic Cloud and Sagittarius

The Milky Way disc is asymmetric about the midplane. The HI shows a warp and recent star count surveys show that the disc is rippled (both in height and streaming vertical velocity). Their respective origins are still not settled. I will show results that suggest that all these features in the disc are shaped by its two most massive satellites. I will present the first self-consistent N-body models of the MW and LMC pair in a first infall scenario designed to study the response of the disc to different mass models. I will show that a massive LMC of virial mass 2.5x10^11 Msun predicts a warp with the correct phases as the observed HI warp but no ripples. However, discrepancies remain between the models and the data, and I will discuss some possible reasons. By contrasting the response of the disc with a heavy Sgr model I will also show that no single interaction model (MW+LMC/MW+Sgr) can capture all the features seen in the disc and that one should consider the collective effect of both satellites. I will then present some revised models of Sgr interacting with the MW that I am now using to study the coupling between the LMC and Sgr on the galactic disc (Laporte et al. in prep).

2016 Nov 23
15:30

Special Seminar: L.C. Popovic

(Astronomical Observatory, Belgrade)

Spectropolarimetry of Type 1 AGNs: AGN central structure and mass of black hole

Spectropolarimetry is a powerful tool for probing the central part of active galactic nuclei (AGNs), since polarized light provides information about the radiation that is coming from the center of an AGN and from the scattering region assumed to be between the central source and the observer. I will present our recent investigation of Type 1 AGNs (with broad emission lines) using spectropolarimetric observations: First, I will discuss the results of multi-epoch spectropolarimetric observations of the radio-loud active galaxy 3C 390.3 (in the period 2009-2014) and Mrk 6 (observed from 2010 to 2013), and after that I will present a new method for measuring SMBH mass using the polarization of the AGN broad emission lines.

2016 Nov 22
16:00

Special Seminar: Haimin Wang

(NJIT/Big Bear Solar Observatory)

Recent Research Results with 1.6m New Solar Telescope at Big Bear

2016 Nov 17
14:30

9th AIP Jamboree

Who does what

The ninth round of speakers:

Friedrich Anders, Anke Arentsen, Rainer Arlt,
Metin Ata, Nicolas Azais, Horst Balthasar,
Sam Barden, Sydney A. Barnes, Regina von Berlepsch,
Ekaterina I. Dineva, Fadil Inceoglu, Petri Käpylä,
Martin Lüders, Kasper Borello Schmidt, Greg Smith

You can download the talks here (pdf, 12 MB).

2016 Nov 15
14:00

Special Seminar: Mahmoudreza Oshagh

(University Goettingen)

Impact of stellar surface inhomogeneities on the determination of exoplanet's parameters

Stellar surface inhomogeneities can cause difficulties in detecting and accurately characterizing the planetary systems through spectroscopic and photometric observations. I will discuss how these inhomogeneities can lead to inaccurate estimation of planetary parameters (e.g., the planetary mass, planet's radius, orbital inclination, and spin-orbit angle). I will also talk about how the stellar active regions can affect the transmission spectroscopy’s measurements and how easily can mimic the signature of Rayleigh scattering in the planetary atmosphere.

2016 Nov 10
14:30

Carlos Allende Prieto

(IAC)

Think thick, think thin. Does the Galactic disk have two discrete components?

The fall in density of stars away from the Galactic plane is well-described by two exponentials, but do they really correspond to two independent stellar populations? In the solar vicinity the two components have distinct, but overlapping distributions in location, velocity, age and overall metallicity, while showing remarkably different abundance ratios. I will report on recent results based on large samples, with high precision measurements of abundances and kinematics, reaching far beyond the solar neighborhood.

2016 Nov 10
10:00

Special Seminar: Tim Birks

(University of Bath, UK)

Optical fibres for astrophotonics

Optical fibres are a common technology for transporting light from one place to another. I will describe how careful design, fabrication and processing of fibres allows us to control the size, shape and number of the modes that they carry, and how this may lead to all-fibre components that enhance or replace the roles of conventional optics in astronomical instruments.

2016 Nov 09
11:00

Special Seminar: Marius Cautun

(Durham University)

The Galactic satellites: a problem for LCDM?

I will discuss two puzzling Local Group observations that appear to be in disagreement with LCDM: a large fraction of satellites seem to rotate in a thin plane (the "plane of satellites" problem) and the lower than expected ellipticity of the satellite orbits (the "satellite ellipticity" problem). The first of the two has received a lot of attention, with several studies claiming that the plane of satellites of the Milky Way and M31 are exceedingly rare in LCDM. These results are based on incorrect statistics: not considering the "look elsewhere effect" and performing a posteri defined tests. Accounting for these effects leads to better agreement between observations and theory, but the two observed planes of satellites are still quite uncommon in LCDM. The "satellite ellipticity" problem is a very recent result. The Galactic satellites have tangentially biased motions while LCDM predicts mostly radially biased motions. Less than 2 percent of LCDM systems have tangentially biased motions to the same extent as observed in the Milky Way.

2016 Nov 07 14:00

Special Seminar: Bridget Falck

(Institute of Theoretical Astrophysics, University of Oslo)

Simulating the Large Scale Structure of the Universe

In the past few decades, simulations of large scale structure have played a key role in cosmology. They are required to calculate theoretical predictions of cosmological models in the nonlinear regime of gravitational collapse, and they have become an invaluable tool for developing and calibrating analysis methods for galaxy surveys. Using examples from my research, I will discuss how we can use simulations to study the formation of the cosmic web, develop tests of gravity, and prepare for future surveys such as Euclid that will push the limits of the accuracy we require of large scale structure simulations.

2016 Oct 26
14:30

David Valls-Gabaud

(Observatoire de Paris)

The MESSIER orbiter: lifting the veil on the ultra-low surface brightness universe

The S-class MESSIER satellite has been designed to explore the extremely low surface brightness universe at UV and optical wavelengths. The two driving science cases target the mildly- and highly non-linear regimes of structure formation to test two key predictions of the LCDM scenario: (1) the detection of the putative large number of galaxy satellites, and (2) the identification of the filaments of the cosmic web. The satellite will drift scan the entire sky in 6 bands covering the 200-1000 nm wavelength range to reach the unprecedented surface brightness levels of 34 mag/arcsec^2 in the optical and 37 mag/arcsec^2 in the UV. Many important secondary science cases will result as free by-products and will be discussed in some detail, such as the luminosity function of galaxies, the contribution and role of intracluster light, the cosmological background radiation at UV and optical wavelengths, the molecular hydrogen content of galaxies at z=0.25, time domain studies of supernovae, GRBs and tidal disruption events, the chemical enrichment of the interstellar medium through mass loss of red giant stars and the accurate measure of the BAO scale at z=0.7 with over 30 million galaxies detected in Lyman-alpha at this redshift. It will provide the astronomical community the first space-based reference UV-optical photometric catalogue of the entire sky, and synergies with GAIA, EUCLID and WFIRST will also be discussed. Technical issues will likewise be addressed for possible improvements on the current design.

2016 Oct 14
14:00

Sixth Potsdam - Berlin Astronomical Colloquium

(at AIP)

Program:

14:00
Matthias Steinmetz (AIP)
Welcome address

14:05
Alessandro Airo (TUB)
From Habitability to Bio-­‐signatures: An Earth analogue and Mars exploration study

14:35
Andreas Sander (UP)
Modelling hot star atmospheres: The current and the next generation

15:05
Coffee break

15:35
Matthias Mallonn (AIP)
Spin-­‐orbit alignment of an extra-­‐solar super-­‐Earth

16:05
Jesper Storm (AIP)
Pulsating stars and the extra-­‐galactic distance scale

2016 Oct 13
14:30

Werner Schmutz

(PMOD/WRC)

The solar influence on climate

Do solar radiance variations have an influence on the terrestrial climate? And what is the amplitude of solar variations? The honest answer is that we do not know for sure - but many suspect there could be larger solar radiance variations then we have measured so far. This implies that there would be a solar influence on climate on time scales of hundred to thousand years that we should take into account when assessing climate change. Starting with the well known climatic influence by the Milankovitch cycles, I compare the orbital forcing with what we know about solar variations - including data from experiments built by the PMOD/WRC. The next step is to speculate what the solar variations could be over longer time scales and evaluate what it implies to the terrestrial climate by using climate model simulations.

2016 Oct 12
14:00

Special Seminar: Jonay I. González Hernández

(IAC)

High precision spectroscopy with HARPS-LFC: the solar gravitational redshift

The new class of large telescopes with significantly increased light-collecting power will probably alleviate the photon-noise limitation to high precision spectroscopy. Thus a new, more precise calibration source will enhance science cases that need high precision spectroscopy. Since 2006, a collaboration between ESO, MPQ and Menlo GmbH, that later joined the IAC and more recently the UFRN, has been studying the capabilities of laser frequency combs (LFC) as a calibration source for high-resolution astronomical spectrographs. The LFC attached to the ultra-stable spectrograph HARPS (designed to detect exoplanets using the radial velocity technique, Mayor et al. 2003) has been demonstrated to be a very accurate calibration system, achieving short-term repeatability at the level of 2.5 cm/s (Wilken et al. 2012). One interesting application is the empirical determination of the gravitational redshift of the Sun from accurate measurements of Fe line positions. In this talk I will show some new instrument facilities operating at high spectral resolution together with some science cases that require high precision spectroscopy.

2016 Oct 06
14:30

8th AIP Jamboree (Functional Jamboree)

AIP people and groups who have an official function shall present themselves and their respective role.

The eighth round of speakers:

Internal Scientific Committee (ISC), Works Council, AIP-Cloud (DAS) & Cluster servers,
Laser Safety, Lab Safety, Workplace safety,
Data protection officer, IT User Group, IT Service, Accounts, E-Mail, Website, ...,
Ombudspersons, Equal Opportunities Officers, Colloquia Organisers,
Commissioners for International Scientists, Postdoctoral training, Doctoral training,
PhD representatives, Leibniz Graduate School

You can download the talks here (pdf, 14 MB).

2016 Oct 05 11:00

Special Seminar: Kathryn Kreckel

(MPIA Heidelberg)

The ISM in Nearby Galaxies: An Optical IFU Perspective

To understand how galaxies evolve we must understand the physical processes in the interstellar medium (ISM) that regulate their evolution. Optical integral field spectroscopy allows us to characterize and map the ionized ISM within nearby galaxies, giving us unique insights into the physics of dust, star formation and feedback at the relevant spatial scales (~100pc). Using a new PMAS/PPAK survey of nearby galaxies (FISHPPAK), I will compare with Herschel SED modeling from KINGFISH to trace both the far-IR emission and optical absorption by interstellar dust and place constraints on the dust distribution and geometry. Applying these insights to star formation studies, I present our deep VLT/MUSE mosaic of the nearby grand design spiral galaxy NGC 628. Here we can resolve and fully characterize the physical properties of 428 arm and interarm HII regions, and determine that diffuse ionized gas (DIG) contamination (traced via the temperature sensitive [SII]/Halpha line ratio) can result in significant (70%) changes to the star formation rate measured. Preliminary results comparing well-corrected star formation rates to ALMA CO(2-1) molecular gas observations at 1"=50pc resolution trace the Kennicutt-Schmidt star formation law at the scales relevant to the physics of star formation. Finally, combined optical and far-IR IFU observations reveal how stellar feedback in NGC 2146 launches a starburst driven galactic wind out to 2.5 kpc above the galaxy disk, with energetics and kinematics that will clearly impact the evolutionary future of the system. In total, by exploiting optical IFU data we trace the full cycling of material through the ISM.

2016 Sep 29
14:30

Tobias Fritz

Constraining halo and satellite properties with proper motions

The most reliable means by which to constrain the properties of the Milky Way dark halo is through assessing the 6-D phase space distributions of tracers of its gravitational potential. This requires accurate proper motions in addition to (generally known) radial velocities for field stars and satellites widely distributed throughout the halo. When only radial velocities are used it is difficult to constrain the properties of the halo due to projection effects along the line of sight. Proper motions allow us to make accurate measurements of anisotropy and thus the total mass of the MW halo. Additionally, they allow us to determine the orbits of objects in the halo, which gives us clues to their origins and to the build up of Milky Way mass.

I will discuss the results of our efforts to obtain proper motions for a variety of tracers in the Milky Way halo, using different telescopes: the LBT, HST, and Gemini South. In the case of the Gemini South Large program we use the novel technique of measuring absolute proper motions relative to background galaxies developed for adaptive optics images. I will present results of three targets thus far: the globular clusters Palomar 5 and Pyxis. From the results on Palomar 5 follows that the inner halo of the Milky Way is consistent with being spherical and that the rotation velocity is about 218 km/s at 20 kpc, the approximate apocenter of the orbit of Palomar 5.

2016 Sep 22
14:30

Petri Käpylä

(AIP)

Cracking the convective conundrum

Convection plays a crucial role in many processes in stellar physics: it is responsible for generating differential rotation and it is thought to facilitate the growth of stellar magnetic fields via a turbulent dynamo. Convection also mixes the stellar matter efficiently which is important in many phases of stellar evolution.

Current stellar models rely on mixing length models which predict a convection zone depth of 200Mm in the the Sun coinciding with helioseismic constraints. This implies that the largest convective scale, or so-called giant cells, should be excited at that scale. Recent helioseismic results, however, suggest very weak amplitudes for velocities at large scales. Furthermore, three-dimensional numerical simulations of stellar convection yield much higher velocities and struggle to reproduce observed large-scale effects such as solar differential rotation. This discrepancy between observations and theory has been dubbed the `convective conundrum.'

This issue suggests that either the theory of stellar convection is fundamentally flawed or that the current simulations of stellar convection are too unrealistic or too far removed from stellar parameter regimes to be of practical use. However, all of these aspects are likely to be closely intertwined and that the solution requires improvements in all of them. The aim of the talk is to review current developments in stellar convection theory that can crack the convective conundrum.

2016 Sep 13
11:00

Special Seminar: Peter Creasey

(University of California at Riverside)

Self-Interacting Dark-Matter as a Mechanism for Dwarf Cores

The Lambda Cold Dark Matter theory has condensed as the central paradigm of cosmology, providing an evolutionary description that is tractable to numerical simulation. The self-similarity of the dark matter halos that emerge from this - in terms of their (i) mass function, (ii) satellite mass function and (iii) inner density slopes - appear difficult to simultaneously reconcile with low mass galaxies, even with the invocation of baryonic effects. One mechanism that can alleviate the tension between these and observed dwarfs is the inclusion of self-interaction channels for cold dark matter.

2016 Sep 08
14:30

David Buscher

(Cavendish Laboratory)

Prospects for science with the Magdalena Ridge Observatory Interferometer

The Magdalena Ridge Observatory Interferometer (MROI) is a long-baseline optical/infrared interferometer under construction at a high-altitude site in New Mexico, with a broad science mission including near-Earth, galactic and extragalactic targets. I will discuss a number of example science programmes with the interferometer and briefly indicate how the design of the MROI makes it a unique instrument for its scientific role. I will discuss the latest status of the project and routes for external scientists and technologists to get involved.

2016 Sep 06
16:00

Jack Lissauer

(NASA Ames)

Kepler's Multiple Planet Systems & PLATO-Kepler Synergies

The primary objective of the Kepler Mission was to determine the abundance of planets within 1 AU of their stars as a function of planetary size, orbital period, and stellar mass.Kepler has made great advances in this area, and has also yielded a bounty of knowledge regarding the properties of planetary systems.More than one-third of the 4700 planet candidates found by NASA’s Kepler spacecraft are associated with target stars that have more than one planet candidate, and almost all of the candidates in such “multis” are indeed true planets.The large number of multis tells us that flat multiplanet systems like our Solar System are common. Virtually all of the candidate planetary systems are stable, as tested by numerical integrations that assume a physically motivated mass-radius relationship. Statistical studies performed on these candidate systems reveal a great deal about the architecture of planetary systems, including the typical spacing of orbits. The characteristics of some of the most interesting confirmed Kepler multi-planet systems will be highlighted. ESA’s Plato Mission will further advance our knowledge of planets and planetary systems.Synergies between Kepler and Plato observations of the same target stars have the potential to provide the best constraints on the abundance of planets similar to Earth and on the properties of a wide variety of planets and planetary systems.

2016 Sep 06 10:00

Special Seminar: Ettore Pedretti

(Heriot Watt University, Edinburgh)

Stellar imaging with the IOTA and the CHARA inteferometer: from model fitting to model independent imaging

The Infrared Optical Telescope Array (IOTA) was composed of three telescopes with a maximum baseline of 38 metres. IOTA became a testbed for new technologies, in particular fibre beam combiners, integrated-optics beam combiners and state-of-art infrared cameras. Although IOTA contributed to the understanding of evolved stars, binary stars and young stellar objects, it had very limited imaging capabilities and relatively short baselines. Due to the limited Fourier coverage afforded by three telescopes only model-dependent imaging was really possible. The Center of High Angular Resolution Astronomy (CHARA) with its six telescopes and baselines up to 330 metres represented a "coming of age" for infrared interferometry. For the first time main sequence stars, interacting binaries, transiting discs and transiting star-spots could be imaged. I will show the evolution of infrared stellar imaging from an "interferometrist" perspective and discuss applications of technologies developed for astronomy to healthcare and micro-endoscopy.

2016 Sep 02 11:00

Kenji Bekki

(University Western Australia)

Formation of globular clusters with multiple stellar populations

Globular clusters (GCs) have long been considered to be single stellar populations (SSPs) - collections of coeval and chemically homogeneous stars. Recent photometric and spectroscopic observations, however, have revealed that most of the Galactic GCs contain at least two different stellar populations with difference chemical abundances, and possibly, different ages. I will discuss the following three topics related to this recent discovery of multiple stellar populations of GCs. First, I will show our new observational results on the presence of multiple-generation of stars in star clusters of the Large Magellanic Cloud. Second, I will show the results of numerical simulations on the two-stage formation process of GCs in gas-rich dwarf disk galaxies. Third, I will discuss how the `anomalous GCs' with metallicity spreads can be formed within their host galaxies using our latest simulations of GC merging.

2016 Aug 04
14:30

Dmitri Pogosyan

(University of Alberta)

Cosmic Web: skeleton, non-gaussianity, connectivity

In this presentation I will talk about geometrical measures of the Cosmic Web of the large scale distribution of matter in the Universe and its filamentary skeleton, how far can we advance the theory to account for non-Gaussianity of the evolving Web and discuss the ongoing recent work on connectivity of the filamentary bridges between the cluster nodes of the Web.

2016 Jul 27
11:00

Special Seminar: Anne Hutter

(Swinburne)

Constraints on cosmic reionization from Lyman-alpha emitters and the 21cm signal

The Epoch of Reionization marks a cataclysmic event in the history of the Universe. Since reionization affects all subsequent structure formation through a number of feedback effects, it is crucial to pin down the topology of reionization. However, the exact progress of reionization and the nature of galaxies driving reionization remain open questions due to a poor understanding of the escape fraction of ionizing photons from the galaxies. Future radiointerferometers such as SKA will measure the distribution of the neutral hydrogen sensitive 21cm signal, which will allow us to derive ionization maps and their time evolution. In this talk I will present a model for high redshift galaxies during reionization and discuss constraints on galaxy properties (e.g. escape fraction of ionizing photons, dust in the ISM) and reionization from Lyman-alpha emitter observations and 21cm maps. In particular I will adress: Which galaxies are identified as LAES and where are those located in the IGM during reionization? Can we derive constraints on reionization and its topology from 21cm and LAE data?

2016 Jul 21
14:30

Nicolas Martin

(Observatoire Astronomique de Strasbourg)

Towards using Local Group dwarf galaxies as a cosmological probe

The salience of satellite dwarf galaxies for understanding galaxy formation in a cosmological context has been made all the more evident in the past decade with the discovery of numerous faint Local Group galaxies. These faint systems are not only important to understand the faint end of galaxy formation but also their distribution around their host can test the hierarchical formation induced by the favored cosmological paradigm. I will review our successful effort to mine the two most ambitious surveys of the surroundings of the Milky Way and Andromeda galaxies, Pan-STARRS1 and PAndAS, for numerous new dwarf galaxies, before presenting the updated tally of MW/M31 satellites and what they are starting to tell us about galaxy formation in a LCDM universe.

2016 Jul 20
14:30

Special Seminar: Alyssa Drake

(CRAL Lyon)

The Lyα Luminosity Function in the MUSE Deep Fields

The study of Lyman Alpha Emitters (LAEs) offers a valuable insight into the early stages of galaxy formation, and with first-year science results from MUSE we have now entered a new era in the detection of these distant faint galaxies. I will discuss the robust, automated detection of 56 LAEs in the MUSE deep-field blind spectroscopic data, and our estimates of these objects’ Lyα fluxes. I will describe our approach to determining the detection-completeness of the LAE sample, and show the MUSE LAE-Selection Function in the Hubble Deep Field South (HDFS). Using this homogeneously selected sample, I will present the Lyα luminosity function between z ∼ 3.0 and z ∼ 6.5 in the HDFS, together with preliminary results from the Hubble Ultra Deep Field (HUDF), and discuss comparisons with the literature.

2016 Jul 19
15:00

Special Seminar: Bartosz Dabrowski

(Space Radio-Diagnostics Research Centre University of Warmia and Mazury, Olsztyn, Poland)

POLFAR - Polish LOFAR Consortium

2016 Jul 12
14:30

Special Seminar: R. Michael Rich

(UCLA)

New Perspectives on the Galactic Bulge

2016 Jul 08
11:30

Special Seminar: Saskia Hekker

(Max Planck Institute for Solar System Research)

Asteroseismology of solar-like oscillators: recent results

Asteroseismology — the study of stellar interiors through their global oscillations — has been revolutionised with the launch of dedicated space missions. The CoRoT and Kepler satellites perform(ed) high precision photometric measurements of tens to hundreds of thousands of stars with the aim to detect both stellar oscillations and planets. In this talk I will present the main breakthroughs with respect to solar-like oscillators — stars that have convective outer layers in which oscillations are stochastically excited and put them in context of galactic archeology.

2016 Jul 04 14:00

Special Seminar: Emre Isik

(Istanbul Kultur University)

Sunspot group tilt angles, magnetic flux tubes and the solar cycle

2016 Jun 30
14:30

Carsten Denker

(AIP)

Solar Image Restoration

Image restoration and digital image processing are foundations for data analysis of ground-based solar observations. Image restoration has to be defined in this context. Whereas image enhancement strives to bring out certain features in an image to simplify the extraction of image information, image restoration is the attempt to retrieve information that has been lost or obscured in the imaging process itself. Therefore, image restoration requires a systems approach that takes into account the entire process of image formation including the propagation of light through inhomogeneous media, the properties of the optical system, and the characteristics of the detector. Here, solar astronomy in general and observations with the Vacuum Tower Telescope and GREGOR solar telescope in particular – both at Observatorio del Teide, Tenerife, Spain – will serve as an example of the image formation process. Various image restoration methods and the underlying mathematical models will be introduced and discussed.

2016 Jun 29
15:00

Special Seminar: Jaime E. Forero-Romero

(Los Andes University, Colombia)

Cosmology with the Cosmic Web

The cosmic web is one of the most striking morphological features of the Universe on large scales. It holds cosmological information and also influences the evolution of galaxies within. In this talk I will present different algorithms that can be used to trace the cosmic web both in simulations and observations. I will show three different applications of this cosmic web characterization. First, a general study of dark matter halo shape, velocity and spin alignment with the cosmic web. Second, the study of the place of the Local Group in the cosmic web; a necessary step to understand the seemingly atypical kinematic configuration of the Milky Way, M31 and their satellites. Third, the usage of the cosmic web as a tool to constrain cosmological parameters. I will close by showing prospects about future surveys that will map the cosmic web on large volumes with unprecedented accuracy, focusing on the Dark Energy Spectroscopic Instrument (DESI).

2016 Jun 29
14:00

Special Seminar: A. Bonanno

(INAF Catania)

Magnetic coupling between the interior and the corona in mean-field dynamo theory

Recent spectro-polarimetric observations of magnetic fields in solar-like stars have shown that strong toroidal fields must be generated axisymmetrically.

This is an important challenge for dynamo theory. In this talk a new class of mean field dynamo models with a consistent coupling between the interior and a coronal model is presented. Observational consequences for the findings of See et al. (2016) are then discussed. The possibility that a dynamo generated field hosts a force-free corona is also discussed.

2016 Jun 23
14:30

Brian Chaboyer

(Dartmouth College)

The Evolution of Metal-Poor Stars

Stellar evolution models are widely used to interpret observations of starlight. There is an increasing interest in the first stars which were formed in the universe, and interpretation of these observations requires accurate models of metal-poor stars. The reliability of the derived properties of stars (such as their age or intrinsic luminosity) depends upon the reliability of stellar models to accurate reproduce the conditions which occur within stars. There are a wealth of observations which can used to test the validity of solar type stars, but until recently there were few tests of the reliability of metal-poor stellar models. In this talk, I will discuss two projects which demonstrate the limitations of current stellar evolution models of metal-poor stars.

We have obtained HST FGS parallaxes for 8 metal-poor ([Fe/H] < -1.5) main sequence stars which are relatively close to the Sun. These parallaxes, with a typically accuracy of 100 microarcseconds, are used to determine the absolute magnitude of these main sequence stars and compared to Dartmouth stellar evolution models. As a star evolves up the red giant branch, the convection zone rapidly deepens, and then recedes towards the surface (in mass coordinates). This receding convection zone is predicted to leave behind a discontinuity in the hydrogen abundance, which slows down the evolution of the star, leading to an increase in stellar number counts at the red giant branch bump. This increase in stellar number counts (the red giant branch 'bump') has been observed in HST observations of globular clusters, and these observations are compared to the predictions from the Dartmouth stellar evolution models. This comparison suggests that convective overshoot becomes increasingly important in low-metallicity stars.

2016 Jun 16 14:30

Albert Chuang

(AIP)

Extracting cosmological information from galaxy (and voids) clustering -- towards to a prior free and accurate methodology

The cosmic large-scale structure from galaxy redshift surveys provides a powerful probe of the properties of dark energy and the time dependence of any cosmological model in a manner that is highly complementary to measurements of the cosmic microwave background, supernovae, and weak lensing. The scope of galaxy redshift surveys has dramatically increased in the last decades. We are developing the methodologies which aim to extract the cosmological information with the most robust way in terms of taking care of the priors, observational and theoretical systematics. These considerations would become more important with the increasing observed volume of galaxy surveys. We have applied our methodologies on the latest SDSS-III/BOSS galaxy sample. In addition, we extend our methodologies by considering the impact of varying neutrino masses. In the end of this talk, I would like to mention the works we have done regarding extracting cosmological information from void clustering.

2016 Jun 09
14:30

Marek Kowalski

(HU Berlin)

Mapping the dynamics of the local Universe with SNe Ia

Supernova Ia serve as excellent distance indicators beyond redshift one, yet, they also have a special role in the nearby Universe. I will discuss recent results on determining the Hubble constant and measure bulk flows using nearby SNe Ia from the Supernova Factory, a spectrophotometric survey of SNe Ia. In the second part of the talk will introduce the Zwicky Tansient Facility, an all-sky survey which will start taking data in 2017 and which will provide a new reference for searches of nearby SNe.

2016 Jun 02
14:30

David James

(CTIO)

Blanco 1: An ideal ZAMS Open Cluster in the Era of TESS

Using new UBVI photometry and intermediate-resolution 1-d kinematics, we employ the Tau-sq fitting methodology to establish a new series of photometric ages and distances to the Pleiades-age Blanco 1 open cluster. Our results show that the cluster's photometric age is very similar its lithium depletion boundary age, although the isochrones place the cluster considerable farther than the HIPPARCOS parallax result. Finally, we advocate that Blanco 1 should be chosen as "the" ZAMS cluster for the TESS mission.

Collaborators: Phillip Cargile (CFA), Con Deliyannis (Indiana University - Bloomington), Aaron Steinhauer (SUNY-Geneseo), Imants Platais (Johns Hopkins University), Owen Boberg (Indiana University - Bloomington)

2016 May 26
14:30

Christer Sandin

(AIP)

Identifying, measuring, and correcting for effects of diffuse scattered light

All surface-brightness structures of integrated light are affected by scattered light. Nobody has up to now correctly accounted for all relevant effects of such scattered light - and the implications have turned out to be alarming regarding the origin of diffuse galaxy haloes and their colours. My studies (Sandin 2014, 2015) show that scattered light forms diffuse haloes around all types of galaxies. The point spread function describes the effects and extent of this scattered light, which is of instrumental and atmospheric origin. I will address the properties of the point spread function and its effects on the characterization of the outer faint stellar haloes of galaxies, including edge-on and face-on disc galaxies, and elliptical galaxies. It is only possible to measure real physical components of structures and colours after the scattered-light component has been accurately removed.

2016 May 19
14:30

The involvement of AIP in the E-ELT

Various speakers

2016 May 12
14:30

Rosemary Wyse

(John Hopkins University)

The Cosmological Context of the Milky Way

The Milky Way is a typical large disc galaxy and can be used as a template for understanding how galaxies form. We can obtain much more detailed information about the stars that make up our Galaxy than we can for more distant galaxies. Stars retain memory of the conditions in which they formed and stars of mass like the Sun live for essentially the age of the Universe. We can thus use old stars nearby to probe the early epochs of galaxy evolution, in a very complementary way to direct observations of galaxies at high redshift. I will discuss how observations of stars in the Milky Way and in its satellite galaxies shed light on fundamental questions such as the nature of the dark matter that dominates how galaxies form and evolve, and the stellar initial mas function at high redshift.

2016 May 02
10:00

Special Seminar: Giuseppe Bono

(Univ. of Rome Tor Vergata)

On the metallicity distribution across the Galactic thin disk using classical Cepheids

We present new results concerning the radial gradients (Fe, alpha, s- and r-process elements) across the Galactic thin disk. We use young (classical Cepheids) stellar tracers for which we collected high resolution spectra with UVES at VLT together with similar estimates avaialble in the literature. The investigated elements display well defined negative gradients when moving from the innermost to the outermost regions.

Moreover, we also found that the radial gradients of the neutron capture elements are positive as a function of age (pulsation period). Thus suggesting an age dependence similar to alpha-elements. On the other hand, the slopes of [elements/Fe] vs Galactocentric distance are more positive than for alpha-elements. We discuss plausible working hypotheses to take account of the difference, and perform a detailed comparison with similar abundances for dwarf and giant stars available in the literature. Finally, we discuss the abundance ratio between s- and r-process elements (La/Eu) and between heavy and light s-process elements (La/Y) and outline their impact on the chemical enrichment history of the Galactic thin disk.

2016 Apr 26
11:00

Special Seminar: Kyle Oman

(University of Victoria, Canada)

Missing Dark Matter?

I'll review some recent results from the APOSTLE simulation project highlighting the wide diversity in local isolated dwarf galaxy rotation curve shapes. This diversity is sometimes ascribed to dark matter cores; while I cannot discount this as a possibility, I will argue that at least some of the scatter must be due to observational or modeling systematics that must be addressed before drawing any further strong conclusions.

2016 Apr 21
14:30

Francesca Primas

(ESO, Garching)

Sodium abundances in GC AGB stars: what do they tell us?

Both photometry and spectroscopy have clearly shown that most, if not all, Galactic globular clusters host at least two (likely more) stellar populations, which are characterized by specific chemical features. One of the most documented ones is the anti-correlation observed between sodium (Na) and oxygen (O), which implies the existence of at least a first (Na-poor, O-rich) and second (Na-rich, O-poor) stellar populations, co-existing in the same cluster. Although these features differ among the globular clusters, they have been detected at all evolutionary stages from the Main Sequence/Turn–Off up to the tip of the Red Giant Branch. The only stage at which contrasting results have been reported in the literature is the Asymptotic Giant Branch. Understanding this is key to our attempts to identify the nature of the polluters.

I will present the results of a new spectroscopic analysis of Na abundances in globular clusters. Our focus is on the comparison of the Na distributions in Asymptotic vs Red Giant Branch stars, in order to verify the presence or lack thereof of Na-rich (second population) stars on the AGB and how they compare to the RGB phase. Our results will be discussed in light of different theoretical predictions.

2016 Apr 20
12:30

Special Seminar: Francesca Primas

(ESO, Garching)

Heroes and S-heroes: fostering gendering equality in astronomy

A diverse workforce is key to ensure balanced views, inclusive approaches and in the long run larger economical benefits worldwide. Among the different aspects that make-up diversity, the gender (here, referred generally to men and women) dimension of science and technology has become one of the most important and debated issues worldwide, impacting society at every level. Gender equality at large is one of the eight United Nations Millennium Development Goals, which clearly call for action related to science, technology and gender.

Despite many recent efforts and improvements achieved on the status of women in astronomy (such as the Baltimore Charter, the Pasadena Recommendations and the IAU Resolution B4 that was passed at the General Assembly in Rio de Janeiro, in 2009), most studies continue to show the same patterns of gender disadvantages, both horizontally (per discipline) and vertically (per seniority level).

Astronomy’s prime international organisation – the International Astronomical Union – has recognized and supported the needs and endeavours of female astronomers through the establishment of an Executive Committee Working Group, at its XXV General Assembly in Sydney, Australia (July 2003). An Organising Committee (OC) of typically 10-16 persons manages the activities of the WG.

The mandate of the IAU Working Group on Women in Astronomy is to collect information, propose measures and initiate actions in support of, or to advance equality of opportunity for achievement between women and men in astronomy, in the IAU and in the world at large. I will report on what this WG has achieved so far and what the planned activities are for the next couple of years.

2016 Apr 14
14:30

Anatoly Klypin

(New Mexico State University)

Dark Matter still matters

I will discuss recent trends and directions in large-scale cosmological N-body simulations. Development of new techniques and production of new simulations are driven by ever increasing requirements of present and upcoming large observational projects such as BOSS, eBOSS, DES, Euclid. So far, it was a challenge for the theory to meet the requirements. I will also discuss recent and unexpected results on the growth of the largest dark matter halos in the standard cosmological model.

2016 Mar 24
14:30

Mathieu Ossendrijver

(HU Berlin)

Proto-Integral Calculus in Babylonian Astronomy

On four babylonian tablets from the period 350-50 BCE, the distance that Jupiter travels along the ecliptic is computed with geometrical methods. The planet's changing velocity during 60 days after its heliacal rising is described as a trapezoidal figure in time-velocity space. The distance travelled is computed as the area of this figure. The time in which Jupiter covers half this distance is also computed. These computations may be viewed as precursors to modern integral calculus.

2016 Mar 22 14:00

Special Seminar: Alex Hagen

(Pennsylvania State University)

What Makes a Lyman-alpha Emitter?

We compare the physical and morphological properties of z ∼ 2 Lyα emitting galaxies (LAEs) from the HETDEX Pilot Survey and narrow band studies with those of z ∼ 2 optical emission line galaxies (oELGs) identified via HSTWFC3 infrared grism spectroscopy. Both sets of galaxies extend over the same wide range in stellar mass (7.5 <logM/M⊙ < 10.5), size (0.5 < R < 3.0 kpc), and star-formation rate (∼ 1 < SFR < 100M⊙ yr−1). Remarkably, in all physical and morphological parameters: stellar mass, half light radius, UV slope (β), star formation rate, ellipticity, nearest neighbor distance, star formation surface density (ΣSFR), and specific star formation rate, there are no statistically significant differences between these populations. In particular, in the case of the UV slope, which parametrizes reddening, the lack of difference suggests that Lyα emission is not significant modulated by dust, as is usually assumed. We develop a simple model of Lyα emission that connects LAEs to all high-redshift star forming galaxies where Lyman-α escapes through a fraction of the galaxy and is thus only observable on a fraction of sightlines. We find a average Lyman-α escape solid angle of ΩLyα = 2.4 ± 0.8 steradians, and find this value consistent with those we calculate from other studies. We then compare our models’ predictions with those of computational models. Furthermore, we find both oELGs and LAEs fall above a linear extrapolation of the "main sequence" of star forming galaxies, which could demonstrate that these galaxies are experiencing a starburst, or that there is a change in the main sequence slope at low stellar masses. This could demonstrate that both oELGs and LAEs are drawn from the same star-bursting subset of high-z star-forming galaxies.

2016 Mar 22
11:00

Special Seminar: Fadil Inceoglu

(AIP)

From Cosmogenic Isotopes to Past Variations in Solar Activity

Observations of sunspots since 1610 AD and records of cosmogenic nuclide production on Earth show that the solar activity varies with a period of ~11 years. This cyclic activity is also found to be modulated on longer time-scales in connection with grand solar minima and maxima, such as the Maunder Minimum (1645-1715) and the Medieval Maximum (1100-1250), respectively, which coincided with the cold period known as the Little Ice Age (ca. 1500-1850 AD) and the warm Medieval Climate Anomaly (ca. 950-1250 AD) in the North Atlantic region.

Information on solar variations prior to 1610 relies on past production rates of cosmogenic nuclides, such as 10Be and 14C. Cosmogenic nuclides are produced in the atmosphere by interactions of galactic cosmic ray particles from space with atmospheric elements, such as N and O. Their production rates are inversely correlated with solar magnetic activity and the geomagnetic field intensity due to the non-linear shielding effect of the solar magnetic field and the geomagnetic dipole field.

During this talk, I will introduce cosmogenic radionuclides and what we can learn from them, focusing on the occurrence characteristics of grand solar minima and maxima during the Holocene (last ~11 kyr) based on simultaneous changes in solar modulation potential reconstructions from 14C and 10Be records.

2016 Mar 16
11:00

Special Seminar: Manolis Papastergis

(Kapteyn Institute/Univ. of Groningen)

The too-big-to-fail problem is too-persistent-to-die: new constraints from nearby field dwarfs

The “too big to fail” (TBTF) problem is a pressing observational challenge to the standard cosmological model at small scales. Put simply, it refers to the fact that it is very challenging to explain both the internal kinematics and the observed number density of dwarfs in the LCDM context. Even though the problem was first identified in the satellite population of the Milky Way, it has now become clear that it concerns dwarf galaxies in general. In this talk, I first plan to give an overview of the observational evidence that supports the statements above. I then plan to briefly describe the most promising solutions to the problem, including a “baryonic” solution within LCDM as well as alternative dark matter models. I will conclude by showing how present and future observations of HI in nearby field dwarfs can help us distinguish between a cosmological and an astrophysical solution for TBTF.

2016 Mar 14
11:00

Special Seminar: Remco van den Bosch

(MPIA)

The grand unified delusion of super-massive black holes and their host galaxies

2016 Mar 07 11:00

Special Seminar: Mario Abadi

(IATE, Cordoba)

Cosmological Numerical Simulations of barred galaxy formation

More than half of the present day spiral galaxies have a stellar bar in their inner region. From the theoretical point of view, bar formation and evolution is still an open question that is far from a definitive answer.Cosmological numerical simulations of galaxy formation give the opportunity to study their origin and evolution. I will present some results about the properties of simulated disk galaxies using the EAGLE set of cosmological N-body/dynamical simulations which show a wide range of bar strength, size and pattern speed. Although, bar formation correlates strongly with the properties of the galaxy dark matter halo we are still far from a unique predictive recipe.

2016 Mar 03
14:30

Huirong Yan

(Uni. Potsdam & DESY)

Tracing astrophysical magnetic field with atomic alignment

I would like to present a new technique of studying magnetic fields in interstellar and intergalactic gas/plasma. This technique is based on the alignment (in terms of their angular momentum in the ground state) of atoms and ions with fine or hyperfine splitting of the ground state. A unique feature of this technique is that the properties of the polarized radiation (both absorption and emission) depend on the 3D geometry of the magnetic field as well as the direction and anisotropy of incident radiation. I shall outline the prospects of the technique and its possible application to studies magnetic fields within circumstellar regions, interplanetary medium, interstellar medium, intergalactic medium. Both spatial and temporal variations of turbulent magnetic field can be traced with this technique as well. In addition, I shall demonstrate that atomic alignment induced by anisotropic radiation can cause polarisation of the radio/far-infrared magnetic dipole transitions within the ground state, thus providing a possible way to study magnetic fields in environments where other techniques fail, e.g. at the epoch of Universe reionization. Last but not the least, we find line intensities are modulated by magnetic alignment as well. Chemistry studies based on spectrometry should thereby account for the influence of magnetic field.

2016 Feb 25
14:30

R. Wimmer-Schweingruber

(Uni. Kiel)

The Mars Science Laboratory and Future Human Exploration

Mars Science Laboratory's rover, Curiosity, landed successfully on Mars on August 6, 2012, and has since been exploring Gale crater. This landing site has proven highly promising for understanding the climate of Mars some 3.7 billion years ago and parts of its following history. The Radiation Assessment Detector, RAD, characterizes the complex spectrum of surface radiation and thus serves to prepare for future human exploration. In my talk I will report on selected first results from MSL and RAD.

2016 Feb 18 14:30

David Martinez-Delgado

(ARI-University of Heidelberg)

Stellar tidal streams in the halos of nearby spiral galaxies

Within the hierarchical framework for galaxy formation, merging and tidal interactions are expected to shape large galaxies up to the present day. While major mergers are quite rare at present, minor mergers and satellite disruptions - that result in giant stellar streams - should be common, and are indeed seen in the halos of the Milky Way and the Andromeda galaxy. In the last years,the Stellar Tidal Stream Survey (PI. Martinez-Delgado) has obtained ultra-deep, wide-field imaging of some nearby Milky Way-like galaxies, based on data taken with a network of small robotic telescopes (0.1-0.5-meter). These images have revealed for first time external views of such stellar tidal streams at unprecedented sensitivity and detail, and provide an opportunity to estimate the frequency, morphology and stellar mass distribution of these structures in the local universe.

In this talk, I will present the latest results our systematic survey of stellar streams, and from N-body modeling of the most striking tidal features. I will also discuss what we can learn from the comparison of our observations with the predictions from L-CDM cosmological simulations of stellar halos, that is the ultimate objective of this project.

2016 Feb 17 14:00

Special Seminar: Oliver Gressel

(Wempe award recipient 2015)

How we think planets are formed

2016 Feb 11 14:30

Yehuda Hoffman

(Hebrew University of Jerusalem)

CLUES @ 2016

The Constrained Local UniversE Simulations (CLUES) project has come of age. Recent advances on the following fronts are to be reported: data (Cosmicflows-2), methodology(likelihood analysis of data, Malmquist bias correction), constrained initial conditions (ICeCoRe, RZA, Ginnungagap), cosmography (large scale structure, cosmic web) and simulations. A major achievement of the CLUES is its ability to produce simulated Local Group (LG) - like objects abundantly and almost ’on demand’. Some of the products of our LG Factory are to be presented.

2016 Jan 28
14:00

Senthamizh Pavai Valliappan

(AIP)

Analysis of historical sunspot observations over four centuries

The study of sunspots with latitudes, areas and group properties like tilt angles over many solar cycles can help us understand the relation between the dynamo and surface magnetic fields. With the improvements for the sunspot group properties, obtained from long term solar activity studies, simulations of the polar-field and open-flux can be performed. The great variability in the solar activity, with grand minima and maxima, can also be studied in detail. Historical data by Scheiner, Hevelius, Staudacher, Zucconi, Schwabe, and Spoerer deliver us the sunspot properties during the 17th - 19th century. We find that the average tilt angles before the Maunder minimum were not significantly different from the modern values. However, the average tilt angles of a period after the Maunder minimum, namely for cycle 0 and 1, were much lower and near zero. The normal tilt angles before the Maunder minimum suggest that it was not abnormally low tilt angles which drove the solar cycle into a grand minimum.

2016 Jan 21 14:00

Matt Hayes

(Stockholm University)

Detecting and characterizing gas accretion and feedback in galaxies

Star formation in galaxies is driven and regulated by the competing forces of gas infall and outflow. On the one hand star-formation must be related by the rate at which gas can be acquired by dark matter halos, cooled, and then compressed into stars. On the other hand, feedback from the star formation process itself heats and accelerates gas in the ISM, which regulates subsequent star formation and shapes the observed relations between the properties of galaxies. I will present and discuss two new observations that concern gas moving in both directions.

* On the inflow side I will present recent observations obtained with VLT/MUSE, the remarkable sensitivity of which enables us to detect a large (~200 kpc) filament of diffuse Ly-alpha emitting gas at redshift 3. I will argue that this gas may fuel the rapid assembly of galaxies inside a high-z protocluster.

* On the outflow side I will present HST observations of warm (log T/K~5.5) gas, as it flows out from a galaxy. Here we map the emission in the OVI phase for the first time. The the unique combination of emission and absorption allows us to measure the physical sizes and cooling rate of the coronal gas phase, and place new constraints on the future (position and state) of gas entrained in galaxy outflows.

2016 Jan 20 12:00

Special Seminar: Calen Henderson

(NASA/JPL)

Campaign 9 of Kepler's extended K2 Mission: A Simultaneous Space- and Ground-based Microlensing Survey

Campaign 9 of K2 (K2C9), the extended mission of the Kepler spacecraft, will conduct a 3.4 square-degree survey toward the Galactic bulge from 7April through 1July this year that will leverage the spatial separation between K2 and the Earth to simultaneously observe ~120 microlensing events, including several planetary in nature as well as many short-timescale microlensing events, which are potentially indicative of free-floating planets (FFPs). These measurements will in turn allow for the direct measurement of the masses of and distances to the lensing systems, quantities that are not typically measured for most microlensing events detected by ground-based surveys alone. I will provide an overview of the K2C9 space- and ground-based microlensing survey and specifically detail the demographic questions that can be addressed by this program, including the frequency of FFPs and the Galactic distribution of exoplanets, the observational parameters of K2C9, and the array of ground-based resources dedicated to concurrent observations. Finally, I will outline the avenues through which the larger community can become involved, an generally encourage participation in K2C9, which constitutes an important pathfinding mission and community exercise in anticipation of WFIRST.

2016 Jan 13 08:30

Mini Symposium on Computational Cosmology

Program

  • 08h30 - 09h15
    PD. Dr. Christoph Pfrommer
    (HITS, Heidelberg)
    “The physics of galaxies and galaxy clusters”
  • 09h15 - 10h00
    Dr. Michaela Hirschmann
    (IAP, Paris)
    "The impact of energetic phenomena on the evolution of galaxies and BHs – a theoretical perspective"
  • 10h00 - 10h45
    Dr. Shy Genel
    (Columbia University, New York)
    “Accretion on Cosmological Scales”
  • 13h45 - 14h30
    Prof. Dr. Mark Vogelsberger
    (MIT, Cambridge MA)
    "The Era of Large-Scale Cosmological Simulations – exploring large and small scales simultaneously"
  • 14h30 - 15h15
    Dr. Sijing Shen
    (UC, Santa Cruz)
    “The formation and baryon cycles of dwarf galaxies”
  • 15h15 - 16h00
    Prof. Dr. Andrea Macciò
    (New York University, Abu Dhabi)
    “Galaxy formation in a Dark Universe'”