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Annual Fall Meeting and 82nd General Assembly

Deciphering the Universe through Spectroscopy

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Programme - Splinter meeting ACT

Exoplanets, stellar activity, and the star-planet connection

as of April 24, 2017

ACT - "Exoplanets, stellar activity, and the star-planet connection"
M. Ammler-von Eiff, N.C. Santos, S.G. Sousa, J. Fernandes, T. Guillot, G. Israelian, M. Mayor, C. Melo
A homogeneous spectroscopic analysis of host stars of transiting planets (Talk)
We present a homogeneous spectroscopic determination of the properties of 13 stars harbouring transiting planets. Such work becomes increasingly important in extra-solar planet research. The iron excitation and ionization equilibria were imposed on spectra with high resolution and high signal-to-noise ratio yielding effective temperature, surface gravity and iron abundance. The new results call attention to some previous determinations of planetary radii and the iron abudance scale of the TrES and HAT objects. 11 further host stars of transiting planets have been studied before using the same methods, giving in total 24 uniformly analyzed stars which follow well the known metal-rich distribution of planet host stars.

ACT - "Exoplanets, stellar activity, and the star-planet connection"
R.I. Anderson, A. Reiners, S.K. Solanki
Zeeman broadening in optical spectra of F- & G-type Stars (Poster)
Magnetic field detectability in solar-like stars is investigated by measuring Zeeman broadening. We perform spectral line inversion of high-quality optical CES data using SPINOR to construct χ2-maps for grids of fixed average magnetic flux densities, Bf. 3σ upper limits for the Sun and 61 Vir (G6V) are established at Bf = 250 G and Bf = 150 G, respectively. A detection of Bf = 500 G is made for 59 Vir (G0V). First direct evidence for a magnetic field in a late F-type star is found in HD 68456 (F6V) with Bf ~ 1 kG. 3σ errors on Bf range between 150 G and 450 G. Results are compared to previous measurements, where available. We conclude that Zeeman broadening remains difficult to detect, even given the present data quality and sophistication of radiative transfer treatment.

ACT - "Exoplanets, stellar activity, and the star-planet connection"
R. Arlt
The solar activity in the 18th century (Poster)
Until recently, detailed information on sunspots has been available starting in 1874. The analysis of about 1000 drawings of the solar disk from 1749-1799 now allows new insights in the butterfly diagram and several other features of solar activity not covered by the mere sunspot number. A weak cycle, hidden in the very long Cycle 4, has been detected using the spot positions. Implications for the variability of the solar dynamo are discussed.

ACT - "Exoplanets, stellar activity, and the star-planet connection"
J. Bean
The CRIRES search for planets around the lowest-mass stars (Talk)
We are currently carrying out a search for planets around the lowest-mass stars using the CRIRES instrument at the VLT under the auspices of an ESO Large Programme. The main purposes of this work are to illuminate the correlation between stellar mass and planet formation, improve the census of planets, and identify new planets that can be followed-up for detailed study. We have developed and are utilizing a new type of gas cell for obtaining high-precision radial velocities of late-type stars in the nIR spectral region. Observations in the nIR offer the advantages in that the targetted stars are bright enough for high-precision spectroscopy, and potential the noise contribution from stellar activity is significantly reduced. In this talk I will present preliminary results from the project, and in particular the work to obtain radial velocity precisions better than 10 m/s for stars at the bottom of the main sequence for the first time.

ACT - "Exoplanets, stellar activity, and the star-planet connection"
J. Cabrera and the CEST team
Additional science with CoRoT light-curves of planetary hosting stars (Talk)
The CoRoT satellite was launched on December 2006 with two goals: to search for extrasolar planets and study the interior structure of stars. So far, six planets and a brown dwarf (with 20 Jupiter masses) have been reported and several results on stellar seismology are published. This presentation focus on the planetary science raised by a careful study of the CoRoT light curves: the thermal structure of the planet through the analysis of the secondary eclipse, the search for other planets in the system through the perturbations in the ephemeris of transiting planets, the search for reflected light of non transiting planets, the study of the stellar activity of the star, the interactions between the star and the planet and the search for moons and rings around transiting planets.

ACT - "Exoplanets, stellar activity, and the star-planet connection"
T.A. Carroll, K.G. Strassmeier
Simultaneous detection and characterization of exoplanets and the magnetic activity of their host stars using a Doppler-Imaging approach (Poster)
We present an inversion approach for the detection of extrasolar planet transits. This technique uses spectral line profile modeling and the inversion of phase dependent line profile distortions during the exoplanet transit. Similar to the Rositter-McLaughlin Effect it allows to infer a number of planetary parameters. The additional benefit of this approach is the simultaneous characterization of the magnetic activity of the host star which provides more reliable detections of possible planet transits in active systems. We will present a number of synthetic model calculation and also introduce our new principal component deconvolution (PCD) technique which allows to boost the signal-to-noise ratio of individual spectral line profiles by up to a factor of 30.

ACT - "Exoplanets, stellar activity, and the star-planet connection"
Sz. Csizmadia and the CEST Team
Uniqueness of the light curve models of CoRoT planets (Poster)
The CoRoT satellite was launched on December 2006 with two goals: to search for extrasolar planets and study the interior structure of stars. So far, six planets and a brown dwarf (with 20 Jupiter masses) have been reported and several results on stellar seismology are published. To find the elements of a transiting exoplanet (semi-major axis, planet-to-stellar radius ratio, inclination, etc.) from its transit light curve means the search for the minimum of a highly non-linear, multivariate function in an N-dimensional hyperspace. By numerical experiments it can be shown that more than one such minimum usually exist - depending on the noise level. In this talk the results of such numerical experiments are presented and the consequences on the planet parameters (mass, radius, average density) are discussed. The detailed modelling results of the CoRoT planets are reported.

ACT - "Exoplanets, stellar activity, and the star-planet connection"
I. Di Varano, K.G. Strassmeier, T. Granzer, M. Woche, D. Fügner, I. Ribas
Recent developments of ICE-T (Poster)
In this poster we present the status of the Ice-T project (International Concordia Explorer Telescope). Simulations of transit light curves have been carried out after having selected the optimal star fields and convolved with the expected instrumental characteristics. For the brightest stars, we showed that ICE-T should be capable of detecting a 2-R_Earth super Earth around a G2 solar-type star, as well as an Earth around an M 0 star - if these targets were as abundant as hot Jupiters. Simultaneously, the telescope can monitor the host star's surface activity in an astrophysically interpretable way. ICE-T is a double Schmidt robotic telescope, 60 cm aperture f/1.1, equipped with a wide field photometer, which will operate during the winter campaign at Dome C. Among the excellent atmospheric qualities of the Antarctic Plateau, the very low scintillation noise permits to reach high photometric precision from 0.1 to 100 mmag in the range between 9th and 18th magnitude. With a 10.3k×10.3k thinned, back-illuminated CCD it will be possible, during the long austral night, to monitor a single FOV of 65 square degrees, including more than 600,000 stars. Primary science cases are extra-solar planets and stellar magnetic activity.

ACT - "Exoplanets, stellar activity, and the star-planet connection"
S. Dreizler
Transiting planets - an overview (Talk)
The detection of transiting planets have boosted our knowledge about extrasolar planets significantly. During recent years, ground and space based transit surveys provided about 60 transiting planets, many of them orbiting bright stars. This enables additional observations allowing to constrain the structure and evolution for a large number of planets. An overview of recent results will given in this talk.

ACT - "Exoplanets, stellar activity, and the star-planet connection"
S. Eggl, E. Pilat-Lohinger, Ch. Theis
The rocky road towards describing late stage planetary evolution in binaries (Poster)
Discoveries of extrasolar planets in double star systems (e.g. Gamma Cephei, HD 41004, Gliese 86) have shifted questions of planetary formation and evolution within binaries into the limelight of scientific interest. Our research is focused on the late stage development of such configurations with special emphasis on Gamma Cephei. We are developing computationally feasible methods to study the systems's long term behavior influenced by remnants of the circumstellar disk. As a model for our numerical investigations, we use the full three body problem including additional drag forces to represent the disk's influence. In order to study the system's stability evolution we apply chaos indicators as well as methods based on the analysis of orbital elements.

ACT - "Exoplanets, stellar activity, and the star-planet connection"
H.-E. Fröhlich, M. Küker, A.P. Hatzes, K.G. Strassmeier
On the differential rotation of CoRoT-Exo-2a (Talk)
We apply a robust spot model to fit with the Bayesian MCMC technique the light-curve of CoRoT-Exo-2a. The spots are assumed long-living and each has its own rotation period. A model with three circular spots reproduces the basic features of the longitude-time spot coverage map. One of the spots exhibits a noticeably lower rotational frequency than the two others. From the rotational frequencies of the three dark features a differential rotation above 0.11 rad/d follows. This is in rough agreement with theoretical models. Mean field models of angular momentum transport by convection and meridional flow lead to an equatorial rotational frequency which exceeds that of the poles by 0.09 rad/d.

ACT - "Exoplanets, stellar activity, and the star-planet connection"
T. Fruth and the BEST team
Ground based support for CoRoT with BEST II (Poster)
The CoRoT satellite was launched on December 2006 with two goals: to search for extrasolar planets and study the interior structure of stars. So far, six planets and a brown dwarf (with 20 Jupiter masses) have been reported and several results on stellar seismology are published. The BEST II system operates as photometric ground based support to the CoRoT space mission. Located at the Observatorio Cerro Armazones, Chile, the telescope performs a precise photometric variability characterization within the selected CoRoT stellar fields prior to the satellite observations. A large field of view provides the possibility of monitoring several thousands of stars with a precision of a few milimagnitudes. The reached precision allows observations of variable stars and in general transiting Jupiter-sized extrasolar planets. We will report on the present status of the project and latest scientific results in the framework of the CoRoT mission.

ACT - "Exoplanets, stellar activity, and the star-planet connection"
S. Gebauer, M. Godolt, J.L. Grenfell, P. Hedelt, P. v. Paris, H. Rauer
On the detectability of biomarkers in extrasolar super-earth atmospheres (Poster)
The presence of biomarker molecules in the atmospheres of terrestrial planets is usually interpreted within the context of biological activity. However, the instrumental design requirements for the detection of such species are demanding because of the weak signals. In this contribution we present detailed studies of spectral resolutions and signal-to-noise ratios achievable with currently proposed space telescopes for emission and transmission spectra of super-earth planets.

ACT - "Exoplanets, stellar activity, and the star-planet connection"
M. Godolt, J.L. Grenfell, A. Hamann-Reinus, M. Kunze, U. Langematz, H. Rauer
Influence of the spectral stellar flux distribution on atmospheric dynamics of extrasolar Earth-like planets (Poster)
Our main goal is to investigate possible Earth-like exoplanet scenarios and spectra taking into account atmospheric dynamics and chemistry. As a first step we use the state-of-the-art 3D General Circulation Model ECHAM5/MESSy (EMAC) to study the influence of spectral flux distributions corresponding to central stars of different spectral type on Earth-like exoplanets. We focus on the atmospheric responses related to surface habitability such as surface temperature, surface wind and precipitation. Preliminary results as well as a comparision with a 1D radiative-convective model will be presented.

ACT - "Exoplanets, stellar activity, and the star-planet connection"
T. Granzer, K.G. Strassmeier, I. diVarano, M. Weber
Chasing a 100 000 stars from a cold place - Ice-T on DomeC (Poster)
Ice-T is a double-Schmidt 60 cm telescope particularly designed to operate on the Antarctic plateau, at the Concordia station, Dome C. The extended long observing period together with the big 10k×10k CCD, operated at exposure times of 10 sec, present a true challenge on data handling, storing and transfer. This talk will summarize possible solutions.

ACT - "Exoplanets, stellar activity, and the star-planet connection"
M. Gyergyovits, E. Pilat-Lohinger, Ch. Theis
Evolution of protoplanetary disks in binary systems (Talk)
We study the evolution of planetary systems around binary stars, once they are established. We are especially interested in the impact of a gaseous disk on the short-term and the long-term dynamics of the planetary system. Therefore we adapted a 2D fluid-dynamical code including self-gravity, for the motion of the disk comoving with the primary star. The location of the embedded planet and the position of the secondary are chosen in agreement with the system Gamma Cephei. We present tests of different implementations and discuss problems, which arise from the interplay of a hydrocode and a N-body solver. We plan to use this code to follow the system's evolution, for a short period of time in order to derive drift rates of the semimajor axis and the eccentricity of the planet for long-term modelling. In a first series of simulations, we vary the orbital elements (semimajor axis, mean anomaly) of the planet, and the masses of the disk and the secondary star. We especially address the evolution of the system near the stability boundaries of the restricted three-body problem, by this shedding light on the impact of a gaseous disk on the long-term stability and evolution of a system like Gamma Cephei.

ACT - "Exoplanets, stellar activity, and the star-planet connection"
A. Hatzes
Extracting signals from the noise: the limits of radial velocity searches for extrasolar planets (Talk)
The radial velocity (RV) method has had spectacular success at discovering over 300 extrasolar planets in the past two decades. A current radial velocity precision of 1-2 m/s is already finding Neptune (15a-20 M_Earth) and Super Earth (5-10 M_Earth) mass planets. New wavelength calibration technologies, such as the laser comb, may increase the RV measurement precision to a few tens of cm/s, giving hope that an Earth mass planet in the habitable zone of a G-type star may one day be discovered. However, RV measurements are limited by intrinsic stellar variability, foremost that caused by stellar activity. The RV `jitter' due to stellar activity can range from 1 to several hundreds m/s, depending on the activity level of the star and this far exceeds the RV amplitude of an exo-earth in the habitable zone of a G-type star. I will present strategies for overcoming this activity jitter and limits of the RV methods. I will show several examples of planets around active stars including some results from the CoRoT space mission.

ACT - "Exoplanets, stellar activity, and the star-planet connection"
R. Heller, B. Jackson, R. Barnes, R. Greenberg, D. Homeier
Tidal effects on brown dwarfs: a possible explanation for the anomalous temperature reversal in the eclipsing binary 2MASSJ05352184-0546085 (Talk)
2MASS J05352184-0546085 (2M0535-05) is the only known eclipsing brown dwarf (BD) binary, and so may serve as an important benchmark for models of BD formation and evolution. However, theoretical predictions of the system's properties seem inconsistent with observations: i. The more massive (primary) component is observed to be cooler than the less massive (secondary) one. ii. The secondary is more luminous (by ~ 1024 W) than expected. Previous explanations for the temperature reversal have invoked reduced convective efficiency in the structure of the primary, connected to magnetic activity and to surface spots, but these explanations cannot account for the enhanced luminosity of the secondary. Previous studies also considered the possibility that the secondary is younger than the primary.
We study the impact of tidal heating to the energy budget of both components to determine if it can account for the observed temperature reversal and the large luminosity of the secondary. We also compare various plausible tidal models to determine a range of predicted properties.
We apply two versions of two different, well-known models for tidal interaction, respectively: i. the `constant-phase-lag' model and ii. the `constant-time-lag' model and incorporate the predicted tidal heating into a model of BD structure. The four models differ in their assumptions about the rotational behavior of the bodies, the system's eccentricity and putative misalignments ψ between the bodies' equatorial planes and the orbital plane of the system.
The contribution of heat from tides in 2M0535-05 may be large enough to account for the discrepancies between observation and theory. The observed luminosity increase of the secondary can be reproduced when we consider contributions from the eccentricity decay and rotational synchronization over a range of the BDs' tidal quality factor Q or time lags τ and possible obliquities ψ2 of the secondary.
Tidal heating may be responsible for the surprising temperature reversal within 2M0535-05. The heating would have slowed down the BDs' shrinking processes and the temperature decrease after the birth of the system ~ 1 Myr ago. More complete modeling of the evolution of these BDs that consistently incorporate tidal effects are required to corroborate our results. Our models suggest connections between the orbital and tidal properties of BDs, providing constraints on tidal dissipation parameters for BDs. For example if tides are indeed responsible for the observed temperature reversal, then we expect few old BD binaries in non-circular orbits. Measurements of the Rossiter-McLaughlin effect for 2M0535-05 can also provide constraints on Q.

ACT - "Exoplanets, stellar activity, and the star-planet connection"
D. Homeier, B. Freytag, F. Allard
Modelling convective transport in substellar atmospheres based on radiation hydrodynamic simulations (Poster)
Convection plays a pre-eminent role in the structure of ultracool atmospheres, starting with the fully-convective late M dwarfs, in which a major part of the emergent energy is carried by convection well into optically thin regions of the atmosphere. While the convectively unstable regions recede again into deeper layers with further decreasing effective temperatures, they are expected to be responsible for the mixing processes that allow condensate clouds to be supported, and that lead to observable deviations from chemical equilibrium mixtures in cooler very-low-mass stars, brown dwarfs and gas giant planets. We present simulations of the velocity field for such atmospheres based on radiation hydrodynamic calculations with the CO5BOLD code, showing overshoot activity well above the Schwarzschild boundary, and a high-reaching turbulence pattern dominated by gravity waves. Feeding these results into the classical 1D atmosphere code PHOENIX, we can provide quantitative predictions of the cloud opacity for brown dwarf and planetary mass objects and of the spectral signatures of tracers of non-equilibrium chemistry, such as carbon monoxide and ammonia.

ACT - "Exoplanets, stellar activity, and the star-planet connection"
M. Hundertmark, F.V. Hessman, S. Dreizler
Information driven sampling of gravitational microlensing lightcurves (Poster)
Galactic gravitational microlensing events magnify the light of source stars located in the Galactic bulge. The high sensitivity for detecting low-mass companions at distances of several kpc makes microlensing an ideal tool for extending our knowledge about the frequency of extrasolar planets. The aim of our work is to illustrate how an optimal sampling of gravitational microlensing lightcurves can be achieved in the sense of the Fisher Information Matrix. This is particularly relevant for planning follow-up strategies within international microlensing collaborations and can help to identify planetary companions around microlenses as soon as possible. For this purpose, we have used Monte-Carlo simulations for determining the Fisher matrix, whose diagonal entries provide lower bounds for the parameter uncertainties. Its evolution for differently sampled lightcurves indicates not only how observational strategies can be optimized, but also when first reliable estimates for a point lens point source model can be obtained.

ACT - "Exoplanets, stellar activity, and the star-planet connection"
V. Joergens
Very low-mass RV companion of the young brown dwarf Cha Hα8 (Talk)
Do brown dwarfs have planets at a few AU? The recent discovery of a very low-mass companion in a close orbit around the very young brown dwarf candidate Cha Hα8 based on UVES/VLT spectra paves the way towards RV planet detections of brown dwarfs. Cha Hα8 is the fourth confirmed spectroscopic companion of a brown dwarf or very low-mass star, and the second known very young one. The companion is likely a very low-mass brown dwarf and might have a mass close to the planetary mass regime. Furthermore, new results of an RV survey for planets of young brown dwarfs and very low-mass stars with UVES/VLT in the Cha I star forming region will be presented. This is based on a recent significant extension of the sample.

ACT - "Exoplanets, stellar activity, and the star-planet connection"
N. Joshi, A. Reiners, B. Goldman
Rotation-activity relation in early- to mid-type M stars (Poster)
We have obtained high resolution optical spectra for a sample of more than 200 early- and mid-type M stars with FOCES (Calar Alto) and FEROS (La Silla). These data will advance our understanding of the rotation-activity relation over a spectral range where stars become fully convective. From our observations we determined the projected rotational velocity (vsin i) and the Hα luminosity, which is directly connected to chromospheric activity, to investigate the rotation-activity relation on both sides of the threshold to complete convection.

ACT - "Exoplanets, stellar activity, and the star-planet connection"
D. Kitzmann, A.B.C. Patzer, P. v. Paris, M. Godolt, J. L. Grenfell, H. Rauer
Effects of clouds on the climate and emission spectra of Earth-like extrasolar planets (Talk)
Cloud particles can have an important impact on the climate of planetary atmospheres by either scattering of the incident stellar radiation back to space (albedo effect) or trapping of IR radiation in the atmosphere (greenhouse effect). Clouds do also have a large effect on the emission spectra of planetary atmospheres, by concealing the thermal emission from the surface or dampening of the spectral features of e.g. biomarker molecules. To study these fundamental effects a parametrized cloud description has been developed and coupled with a one-dimensional radiative-convective climate model including the possibility to account for different amounts of cloud coverages and partial overlap of multilayered clouds. The impact of multilayered clouds in dependence of the cloud coverages on the planetary emission spectra, especially on biomarker signatures, is presented for Earth-like planets orbiting different types of central stars. Implications regarding the clouds influence on the position and extension of their habitable zones are discussed.

ACT - "Exoplanets, stellar activity, and the star-planet connection"
R. Köhler, Th. Henning, D. Queloz, A. Quirrenbach, and the ESPRI Team
Algorithms for micro-arcsecond astrometry with PRIMA at the VLTI (Poster)
Astrometric detection of planets requires a precision of 10-30 micro-arcsec (see Poster by R. Launhardt). For an interferometer with a baseline of 100 m, this corresponds to measuring the (differential) optical path difference with a precision of 5-15 nanometers. This can only be achieved with careful calibration of the instrument, including effects that are irrelevant for almost any other scientific application. Furthermore, we have to take into account a number of astrometric effects, e.g. relativistic light deflection caused by the sun and the planets. We will give an overview of the design of the software, and the methods employed to achieve the scientific goal.

ACT - "Exoplanets, stellar activity, and the star-planet connection"
M. Küker, L.L. Kitchatinov, G. Rüdiger
Differential rotation and meridional flows of young stars (Poster)
Though not a field generator itself, the meridional flow plays a crucial part in the stellar dynamo process. As differential rotation and meridional flow are closely related, theoretical models of stellar rotation also make predictions about the flow. We compare surface rotation laws from theory with recent observations and discuss the predicted meridional flows and their potential impact on the stellar dynamo.

ACT - "Exoplanets, stellar activity, and the star-planet connection"
J. Langfellner, D. Homeier, S. Dreizler
Simulating the Rossiter-McLaughlin effect for transiting planets in eccentric orbits (Poster)
Most of today's known transiting extrasolar planets are in nearly circular orbits around their host stars and are thought to be roughly in spin-orbit alignment. However, exceptions have been found, for instance the systems HD 80606 and HAT-P-2, which show a high eccentricity. Using a spectral synthesis code based on the program `Bruce' by Richard Townsend, eclipsed spectra and light curves of the host stars were simulated to calculate the residual radial velocity due to the Rossiter-McLaughlin effect for these systems, together with the well studied system HD 209458. `Bruce' provides a model of the deformation of the star's surface depending on the effective temperature, the rotation velocity and average surface gravity. The surface is divided in small regions, for each of which a spectrum is calculated for the local atmospheric parameters and radial velocity. These are summed up to form the total emergent (reference) spectrum. If the planetary disk covers a part of the star during the transit, the corresponding regions omitted from the total spectrum at this time. Cross correlation between the reference and the transit spectrum leads to the residual radial velocity. On this poster, the results of the simulations are presented and discussed with regard to observed data.

ACT - "Exoplanets, stellar activity, and the star-planet connection"
R. Launhardt, J. Setiawan, Th. Henning, M. Kürster, A. Müller, P. Weise
Exoplanets and starspots - the case of TW Hya (Talk)
Finding planets around young stars is crucial for our understanding of planet formation. However, their detection is challenging due to the effects of enhanced stellar activity at young ages. We have carried out a systematic radial velocity (RV) survey of nearby T-Tauri stars and developed techniques to disentangle the effects of activity from that of companions. This program has resulted, among others, in the discovery of a giant planet orbiting TW Hya, the nearest classical T-Tauri star that also exhibits a circumstellar disk. The data also show evidence for stellar activity (spots), but smaller amplitude and a different period. However, this discovery has been challenged by others and the question remains under debate whether the data inevitably infer the presence of a planet or can be explained by photospheric activity only. We have critically reanalyzed all data, including new measurements, and discuss the results and arguments.

ACT - "Exoplanets, stellar activity, and the star-planet connection"
R. Launhardt, Th. Henning, D. Queloz, A. Quirrenbach, et al.
ESPRI - the astrometric exoplanet search with PRIMA (Poster)
More than 350 extrasolar planets have been found until today, the vast majority of them with the radial velocity method. Consequently, our knowledge on the properties of extrasolar planetary systems is still heavily affected by the detection biases of this method. However, the dominant role of the radial velocity technique is slowly eroded by the arrival of new facilities. The ongoing developments by European Southern Observatory of the PRIMA dual-feed capability of VLTI will provide us soon with the relevant infrastructure to carry out an astrometric search for planets. This will complement some weakness inherent to the radial velocity method and open new discovery spaces. In order to speed up the full implementation of the astrometric capability of the VLTI and to carry out a large astrometric Exoplanet Search program with PRIma (ESPRI), a consortium lead by the Observatoire de Geneve (Switzerland), the Max Planck Institute for Astronomy, and the Landessternwarte Heidelberg (Germany), has built the Differential Delay Lines (DDLs) for PRIMA and is currently developing the astrometric data reduction software. When equipped with DDLs, PRIMA will be able to perform high-precision narrow-angle astrometry in K-band, reaching a precision of 10-30 μas. It will thus be capable of detecting Saturn and Uranus-mass planets around nearby main sequence stars of any spectral type. Since astrometry does not depend on narrow and stable spectral lines, it will also be sensitive to Jupiter-like planets around young stars. This poster gives an overview of the technical developments and outlines the scientific preparations as well as the goals and prospects of the ESPRI survey, anticipated to start in late 2010, when PRIMA becomes operational.

ACT - "Exoplanets, stellar activity, and the star-planet connection"
F. Lenz, A. Reiners
Star-planet interactions (Poster)
Using Data from the ESO archive and the HET we analyze spectra from HD 209458 and Tau Boo for star-planet interactions. A closely orbiting planet could induce chromospheric activity, due to gravitational or magnetic interaction. Analyzing the Ca ii H & K Lines we search for recurring emission with the same period as P_orb. We present our analysis from archive data of HD 209458, in which we find no signs of periodic Ca ii K Emission, and we show our results from HET data of Tau Boo.

ACT - "Exoplanets, stellar activity, and the star-planet connection"
R. Lutz, S. Schuh, R. Silvotti, and the EXOTIME collaboration
Photometric monitoring of pulsating subdwarf B stars (Poster)
The EXOTIME program is a collaboration of various observers to conduct long-term time-series photometry of selected pulsating horizontal branch objects. Our goal is to search for exoplanets around these evolved stars by studying timing effects and to gain insight on late stage planetary systems. The target list currently includes five pulsating subdwarf B (sdB) stars. Appliying the O-C method, we will also be able to derive evolutionary timescales. Here we will report on our progress in the analysis of the target HS 0702+6043.

ACT - "Exoplanets, stellar activity, and the star-planet connection"
M. Mohler, S. Dreizler, A. Reiners, T. Mazeh, I. Ribas
Improving the mass-radius relation of low-mass stars (Poster)
In recent years efforts to find extrasolar planets steadily increased and still do. For that purpose a huge amount of photometric time-series data was obtained using different survey projects. In case the first analysis ruled out possible involvements of exoplanets, the according data sets were often set aside. These contain many eclipsing binaries with low-mass stellar companions. Several rejected objects of the TrES-survey are now used for mass-radius determinations of several bright eclipsing binaries with low-mass companions. Therefore observations at the Calar Alto Observatory (Spain) with the 2.2 m telescope using the Echelle spectrograph FOCES have been obtained at the end of May 2009. The preliminary results presented on this poster describe the derivation of the radial velocity variations for reliable mass and radius determinations.

ACT - "Exoplanets, stellar activity, and the star-planet connection"
R. Neuhäuser, A. Koeltzsch, St. Raetz, M. Mugrauer
Activity cycles around young stars? (Talk)
With BVRI band photometric data spanning almost 50 years (1960s until 2009), we have reinvestigated the variability of the young, naked, weak-line, run-away T Tauri star Par 1724 just north of the Orion Trapezium. We used archival and published data, new own observations from 0.9-m Dutch telescope on la Silla, the 0.9-m Wendelstein telescope of University Munich, a 25-cm telescope of the University Observatory of Jena, as well as from the ASAS automatic sky survey. The previously known 5.7 day rotation period was confirmed. In addition, evidence for a 9- or 17.5-year cycle was found in both V-band magnitudes and variability amplitude. This would be the youngest star found so far with a cycle. If due to a dynamo, one would expect a small degree of differential rotation, e.g. two apparent rotation periods with a difference of only a fraction of a day. Most recently, we have searched for such a signal in the data and will report the results. In addition, we have started to search for cycles also around other young stars, partly also using archival plates. We will also briefly mention other observing programs at the University Observatory Jena, in particular regarding the activity of stars and the search for exo-planets by transits and transit time and duration variations.

ACT - "Exoplanets, stellar activity, and the star-planet connection"
L. Nortmann, S. Dreizler, A. Reiners
Observations of low-mass and planet host stars with the MONET-Telescope (Poster)
The Institute for Astrophysics Göttingen operates two robotic 1.2 m telescopes at McDonald Observatory and at the South African Astronomical Observatory. This allows us to conduct long-term monitoring to search for stellar variability of all kinds. In this project, we engage in photometric observations of two potential planet host stars of class M, which are simultaneously investigated in an ESO Large Program searching for radial velocity variations of low mass stars. Here we report first results on stellar activity of these targets. Furthermore we present data from a photometric follow-up transit observation of an established planet host star.

ACT - "Exoplanets, stellar activity, and the star-planet connection"
P.v. Paris, M. Godolt, J.L. Grenfell, P. Hedelt, B. Patzer, H. Rauer, B. Stracke
Extrasolar planets in the Gliese 581 system - model atmospheres and implications for habitability (Poster)
The planetary system around the M dwarf Gliese 581 contains at least four planets, three of them are considered Super-Earths with masses between two and seven times the mass of the Earth. The planets Gliese 581 c and d were the first planets which merited a detailed study of their potential habitability. The first published studies concluded that Gliese 581 c was too hot for habitable conditions, whereas Gliese 581 d was located just beyond the outer edge of the habitable zone. However, the orbital distances of the two planets have recently been revised based on a longer radial velocity baseline, putting them about 10% closer to the star (Mayor et al. 2009, submitted to Astronomy & Astrophysics). In order to investigate the habitability of Gliese 581 c and d under these new conditions, we applied a 1D radiative-convective model to potential atmospheric scenarios by varying the surface pressure and atmospheric composition.

ACT - "Exoplanets, stellar activity, and the star-planet connection"
F. Pepe, P. Figueira, C. Lovis, M. Mayor, D. Ségransan, D. Queloz, S. Udry
Extrasolar planets search and characterization (Talk)
Since the discovery of 51 Peg b the search of extra-solar planets has evolved significantly. On the one hand, the number of known exoplanets increases continuously and reaches a level from which statistical properties can be derived. On the other hand, various techniques allow us more and more to also access physical parameters and the atmospheric characteristics of these planets. In my talk I will give an overview of the activities carried out at the Geneva Observatory and try to provide a (certainly incomplete) summary of the current status of the extra-solar planets field.

ACT - "Exoplanets, stellar activity, and the star-planet connection"
A. Quirrenbach and the CARMENES Team
CARMENES: Study of a radial-velocity spectrograph for Calar Alto (Talk)
CARMENES is an ongoing study for a high-precision radial-velocity spectrograph for the 3.5 m telescope on Calar Alto. The main scientific goals of CARMENES are planet surveys of ~ 300 M dwarfs and ~ 3000 K giants. For the M dwarf survey, the brightest objects of mid-M spectral type accessible from Calar Alto will be selected. Their radial velocities will be monitored in the near-infrared (Y, J, and H bands) with a fiber-fed cross-dispersed echelle spectrograph (R ~ 85,000), calibrated with the simultaneous ThAr method. A visible-light spectrograph covering the spectral range from ~ 5,000 to 9,000 Angstroms will provide simultaneous monitoring of variability indicators (mainly H alpha and the Ca ii triplet). In each field, ~ 10 K giants will be selected for simultaneous observations with a multi-object spectrograph covering the wavelength range from ~ 5,000 to ~ 6,000 and stabilized with an iodine cell.

ACT - "Exoplanets, stellar activity, and the star-planet connection"
Th. Ratzka, S. Wolf, B. Lopez, and the MATISSE consortium
Imaging protoplanetary discs with MATISSE (Poster)
MATISSE, the Multi Aperture Mid-Infrared SpectroScopic Experiment, is one of the second generation instruments of the VLT Interferometer. Designed to combine up to four telescopes and operated simultaneously in the N- and the L- or M-band, MATISSE allows the efficient interferometric reconstruction of mid-infrared images. It further offers spectral resolutions of up to 1500. MATISSE is thus a unique tool to investigate the distribution and composition of warm gas and dust around a variety of astronomical objects. Moreover, the mid-infrared images will help to bridge the gap between the images taken at shorter wavelengths with adaptive optics systems at the new ELTs and the millimetre maps provided by ALMA. One of the primary science goals of MATISSE is the study of protoplanetary discs to reveal the evolution of the circumstellar material. Even direct signatures of planets like gaps or planetary accretion discs can be detected with MATISSE, because the contrast between the star and the circumstellar environment is already favourable in the mid-infrared.

ACT - "Exoplanets, stellar activity, and the star-planet connection"
H. Rauer and the CEST Team
The growing CoRoT planetary family (Talk)
The CoRoT satellite was launched on December 2006 with two goals: to search for extrasolar planets and study the interior structure of stars. So far, six planets and a brown dwarf (with 20 Jupiter masses) have been reported and several results on stellar seismology are published. Among the highlights of planet discoveries from CoRoT is a small terrestrial planet, CoRoT-7b, with less than two Earth radii size. The present status of the CoRoT mission, with emphasis on the steadily growing CoRoT planet family, will be reported. In addition, potential observational biases of the two currently most successful planet detection methods, radial velocity and transit search, will be addressed. Finally, an outlook to proposed future transit detection missions (PLATO) and prospects for characterization of transiting terrestrial planets will be given.

ACT - "Exoplanets, stellar activity, and the star-planet connection"
A. Reiners
Detecting planets around active low-mass stars (Talk)
In this talk I will give an overview of the connection between stellar activity and the quest for planets. Stellar activity can produce starspots that are known on the Sun, in other stars they are inferred from photometry and Doppler imaging. The surface features can cause large radial velocity variations that could mimick a planet's signal, and stellar activity could also be caused by star-planet interactions. Low-mass (M-type) stars can be particularly rapid rotators and very active, and I will discuss the perspectives detecting planets around them.

ACT - "Exoplanets, stellar activity, and the star-planet connection"
S. Schäfer, F. Hessman, M. Hundertmark, S. Dreizler
Testing General Relativity by observing gravitational microlensing with long-baseline interferometry (Poster)
Due to the small separations of the observed images of microlensing events, it is difficult to determine all physical parameters from photometric lightcurves alone. With long-baseline interferometry providing a resolution in the milliarcsec range, one can resolve these images and break the mass degeneracy. Microlensing-survey programs like MOA and OGLE detect about 1000 events per year with ~ 10% binary events including planetary companions which are of special interest. Based on simulations we characterise the candidates which are most sensitive with respect to deviations from general relativity and are observeable with the VLTI.

ACT - "Exoplanets, stellar activity, and the star-planet connection"
K. Scherer, S.E.S. Ferereira, H. Fichtner
Different cosmic ray spectra at exoplanet orbits (Talk)
The cosmic ray spectra at the position of an exoplanet depend not only on the stellar activity and the surrounding astrosphere, but also on the local interstellar environment. We discuss here different wind driving stars together with their possible local interstellar media, and the resulting cosmic ray flux at the orbit of an exoplanet. The cosmic ray spectrum has not only influence on lifeforms, but also on the reduction of biomarkers. The latter can be used as tracers for biological activity, and, therefore, their modification by cosmic rays is important to be known.

ACT - "Exoplanets, stellar activity, and the star-planet connection"
S. Schuh, R. Silvotti, and the EXOTIME collaboration
Planetary systems around evolved stars (Poster)
The majority of extrasolar planets are found around hydrogen core burning main sequence stars since this is the longest-lived phase in the live of a star, and the radial velocity method is most readily applied to these host stars. Beyond the main sequence phase, planets have been found around subgiant stars at the beginning of the red giant branch, and the first planet-like objects ever discovered were in fact found around pulsars. In between the highly evolved pulsars, and stars evolved just beyond the main sequence, planetary systems found around extreme horizontal branch stars allow to separate the effects of the red giant branch from those of the asymptotic giant branch evolution.

ACT - "Exoplanets, stellar activity, and the star-planet connection"
U. Seemann, A. Seifahrt, A. Reiners
The Hα limit in the Hyades (Poster)
We present a study of K to M type stars in the Hyades. We use a large sample in this intermediate-age cluster ( ~ 650 Myr) to probe a threshold region where magnetic wind braking becomes ineffective and stars have not yet spun down to the rotation rate found on the main sequence. Our results on rotational velocities (v sin i) and activity indicators (Hα, Ca ii H+K) shed light on the question whether the threshold to rapid rotation in the field stars and the Hyades stars is different.

ACT - "Exoplanets, stellar activity, and the star-planet connection"
B. Stracke , J.L. Grenfell, P. von Paris, B. Patzer, H. Rauer
The inner boundary of the habitable zone for Earth-like planets (Poster)
Liquid water is a commonly accepted, fundamental requirement for the development of life. Based on this condition the Habitable Zone (HZ) is usually defined as the region of orbits around a star where liquid water exists on the surface of a terrestrial planet. The inner boundary of the HZ can be defined in different ways. The `water loss limit' occurs where an Earth-like planet loses its entire water content within the planet's lifetime. The `runaway greenhouse' limit marks the point where the greenhouse effect becomes unstable via water evaporation. We present here a thorough study of the inner boundaries of the HZ around solar-type stars. To investigate these inner boundaries a one-dimensional radiative-convective model of the atmosphere is applied to different planetary system scenarios. Our modelling approach involves the step-by-step increase of the incoming stellar flux and the subsequent calculation of resulting changes in the atmospheric water vapour content and the radiative properties. To achieve this, the infrared radiative transfer scheme was improved to be suitable for such high temperature and pressure conditions. Modelling results are presented for the influence of various planetary and atmospheric conditions on the inner boundaries of the HZs around solar-type stars.

ACT - "Exoplanets, stellar activity, and the star-planet connection"
K.G. Strassmeier, J. B. Rice, M. Kopf, T. Carroll
Doppler imaging the PMS star V410 Tau: a comparison of different inversion codes (Poster)
We present Stokes I and V line-profile inversions of the active pre-main sequence star V410 Tau. The inversion process is based on our two codes TempMap and iMAP. While the former uses either a maximum entropy or Thikhonov regularization based on selected atomic spectral lines, the latter is based on a regularization-free inversion from a principal component analysis of nearly thousand lines. Very good agreement between the images is found. The star was also caught in the action of a large flare that excited and redshifted magnetically sensitive emission lines by 200 km/s and even affecting optically thin lines in their red absorption wings. We also present an inversion map from the molecular bandhead of TiO at 705.5 nm and discuss its relation to atomic lines.

ACT - "Exoplanets, stellar activity, and the star-planet connection"
D. Swoboda, F. Hessman, M. Hundertmark, S. Dreizler
Tests of the Difference Imaging Algorithm (Poster)
The Difference Imaging Algorithm (DIA) is an important technique for obtaining high-precision photometry from large datasets without the need of PSF-Fitting. It is mainly used to detect objects with varying luminosity in dense stellar fields. We have investigated the performance of DIA in very heterogeneous data sets (SNe) and in homogeneous datasets with a known transiting extrasolar planet.

ACT - "Exoplanets, stellar activity, and the star-planet connection"
L. Walkowicz, G. Basri
Stellar rotation and activity with Kepler (Talk)
The Kepler Mission will obtain precise photometry for over 150,000 stars in the next four years. While the mission's primary goal is the search for extrasolar Earths, these data also provide a wealth of information regarding stellar activity. Because of the intimate link between stellar rotation and the generation of the magnetic field, periodic brightness variations due to starspots may be used to gain insight into the magnetic dynamo. However, stellar activity may also conceal the tiny signal of the transits we seek. We present early analysis of stellar activity in the first data from Kepler.

ACT - "Exoplanets, stellar activity, and the star-planet connection"
S. Wende, A. Reiners, P. Bernath
Exact identification of molecular FeH lines in GJ 1002 (Poster)
Molecular FeH absorption provides a large number of sharp and isolated lines to measure radial velocity, rotation, and magnetic field strength with high accuracy. Our aim is to provide an atlas of FeH for M-stars in the spectral range from ~ 986 nm to ~ 1077 nm (Wing-Ford-Band). To identify these lines in the CRIRES spectra of GJ 1002 (a magnetically inactive M 5.5 star), we calculated model spectra for the selected spectral region with FeH line data from Dulick et al. (2003). In general this line list agrees with the observed data, but differs strongly at some line positions. In many cases the line strengths are not well reproduced, too. We will correct the line data for position and line strength to provide an accurate atlas of FeH absorption lines for the use of high precision spectroscopy in low mass stars. To measure magnetic field strengths, we will finally identify the magnetic sensitive FeH lines in a CRIRES spectra of the active M-dwarf GJ 1224 (M 4.5).




last update August 28, 2009, R. Arlt