# News

## ESO Science Release: Looking Deeply into the Universe in 3D

26 February 2015. MUSE goes beyond Hubble

The MUSE instrument on ESO’s Very Large Telescope has given astronomers the best ever three-dimensional view of the deep Universe. After staring at the Hubble Deep Field South region for only 27 hours, the new observations reveal the distances, motions and other properties of far more galaxies than ever before in this tiny piece of the sky. They also go beyond Hubble and reveal previously invisible objects.

Please find more details on the ESO website.

Caption: The background image in this composite shows the NASA/ESA Hubble Space Telescope image of the region known as the Hubble Deep Field South. New observations using the MUSE instrument on ESO's Very Large Telescope have detected remote galaxies that are not visible to Hubble. Two examples are highlighted in this composite view. These objects are completely invisible in the Hubble picture but show up strongly in the appropriate parts of the three-dimensional MUSE data.

Credit: ESO/MUSE Consortium/R. Bacon

## Star passed through solar system 70,000 years ago

18 February 2015. An international team of astronomers around Eric Mamajek from the University of Rochester (USA) found out that our solar system had a stellar visitor very rently, just 70,000 year...

This inconspicuous red dwarf star was discovered last year by Ralf-Dieter Scholz at the Leibniz Institute for Astrophysics Potsdam (AIP) with its present distance of about 20 light years. Eric Mamajek now nicknamed it "Scholz's Star". During its flyby, this star came as close as 0.8 light years (about 10 light months) to the sun and passed the exterior of the solar system, the so-called Oort cloud. For more details see the links and publications below.

Caption:  The new solar neighbour was originally discovered in 2014 at AIP using new data of the Wide-field Infrared Survey Explorer (WISE) and astronomical archives of old photographic plates. It hides in the band of the Milky Way, which is overcrowded by many background stars. Typical of a cool red dwarf, it appears much brighter in infrared light. Despite its proximity, it moves rather slowly on the sky (in direction of the arrow). This was a first hint on a possible recent encounter with the sun. (Credits: AIP, SuperCOSMOS Sky Surveys, WISE)

Publication Mamajek et al. (2015)

Publication Scholz (2014)

Science Contact: Dr. Ralf-Dieter Scholz, +49 331-7499-336, rdscholz@aip.de

Media contact: Kerstin Mork, +49 331-7499-469, kmork@aip.de

The key topics of the Leibniz Institute for Astrophysics Potsdam (AIP) are cosmic magnetic fields and extragalactic astrophysics. A considerable part of the institute's efforts aim at the development of research technology in the fields of spectroscopy, robotic telescopes, and e-science. The AIP is the successor of the Berlin Observatory founded in 1700 and of the Astrophysical Observatory of Potsdam founded in 1874. The latter was the world's first observatory to emphasize explicitly the research area of astrophysics. Since 1992 the AIP is a member of the Leibniz Association.

"Cosmic clock" - artist impression.

## Nature article: How stars reveal their ages

5 January 2015. A recently published study in the scientific journal Nature presents a method by which the age of stars can be determined very precisely: "Gyrochronology", an analytical procedure f...

By observing and surveying 30 cool solar-type stars in the 2.5 Billion-year-old cluster NGC 6819 the international research team led by Søren Meibom of the Harvard-Smithsonian Center for Astrophysics, this method has now been shown to work over a wide age range, significantly improving the accuracy of stellar age determination.

"The relationship between mass, rotation rate and age of the observed stars is now defined well enough that by measuring the first two parameters, the third, the star's age, can be determined with only 10 percent uncertainty," said Barnes. The speed of rotation of a star decreases over time, and also depends on the mass of the star; heavy stars rotate faster than smaller, lighter ones, as a rule. While some aspects of this basic behavior have been known to astronomers for a while, this work has seized an opportunity to test and clarify the precision and accuracy of the method.

The newly released study firmly provides the intimate relationship between mass,rotation rate, and age of the cool star using coeval (same age) cluster stars so that the ages of even non-cluster (so-called field'') stars can be determined. The determination of the rotation rates was carried out by observing changes in brightness caused by star spots on the surface of the observed stars rotating into and out of view. At this age, a typical star changes its brightness by much less than 1 percent. Such precise observations were only possible using NASA's Kepler Space telescope.

This most accurate determination of the age of stars is important in understanding how various astronomical phenomena evolve over time. For example, knowledge of stellar ages can be helpful in targeting the search for life outside our solar system, because it has taken billions of years for the development of the complexity of life on Earth. Planets orbiting stars with ages similar to the sun are therefore seen as particularly promising objects of study.

Caption: This artist's impression of a "cosmic clock" illustrates how astronomers have used stellar rotation to measure the ages of stars in a 2.5-billion-year-old star cluster. Their results, the latest success of gyrochronology, mark the first extension of such observations to stars with ages beyond 1 billion years, and toward the 4.6-billion-year age of the Sun. Being able to tell the ages of stars is the basis for understanding how astronomical phenomena involving stars and their companions unfold over time. (Credit: Michael Bachofner)

Scientific contacts:

Dr. Sydney Barnes, sbarnes@aip.de, +49 157-3076 1230

Dr. Søren Meibom, smeibom@cfa.harvard.edu, +1 617496-4773

Media contact: Kerstin Mork, presse@aip.de, +49 331-7499 469

The key topics of the Leibniz Institute for Astrophysics Potsdam (AIP) are cosmic magnetic fields and extragalactic astrophysics. A considerable part of the institute's efforts aim at the development of research technology in the fields of spectroscopy, robotic telescopes, and e-science. The AIP is the successor of the Berlin Observatory founded in 1700 and of the Astrophysical Observatory of Potsdam founded in 1874. The latter was the world's first observatory to emphasize explicitly the research area of astrophysics. Since 1992 the AIP is a member of the Leibniz Association.

Selected spectrum.

## A universal comb

10 December 2014. Scientists from the Leibniz Institute for Astrophysics in Potsdam (AIP) and the Centre for innovation competence innoFSPEC have tested a novel optical frequency comb using an astr...

"The special quality of the light generated by the optical frequency comb is that it consists of individual, discrete colours, with a precise frequency spacing," explains the responsible innoFSPEC scientist Jose Boggio. „The optical comb is created by the superposition of laser light with two different frequencies.“ The resulting comb spectrum is not continuous, as in a rainbow, but consists of different coloured lines with fixed spacing and dark gaps between - hence the name frequency comb.

To analyse the light from stars and galaxies, all spectrographs must be calibrated using a known light source. "The frequency comb serves as optical ruler that is more stable and regular, than the light from conventional spectral calibration lamps", explains astrophysicist Andreas Kelz. "Thanks to these methods, we will be able to determine the rotational speeds of galaxies or the chemical composition of stars more precisely."

After development in the laboratories of innoFSPEC Potsdam, the frequency comb has undergone a first practical test on sky. During a recent observing campaign at the Calar Alto Observatory in southern Spain, the AIP-built PMAS spectrograph was equipped with the frequency comb. After the successful outcome of these tests, Roger Haynes, head of the innoFSPEC research group, is sure that laser frequency combs will set new standards in  astronomical precision spectroscopy and laboratory analysis.

Back in 2005, Professor Hänsch from the Max-Planck-Institute for quantum optics, received the Nobel Prize for the development of an optical frequency comb. However, the device developed in Potsdam is based on a different principle of operation and produces comb-lines with a much larger pitch. This makes it applicable for typical astronomical night-time spectrograph operating at low and medium resolution.

Caption: Selected spectrum of the optical frequency comb (upper, blue panel) as compared to a Neon spectral lamp emission (lower red panel). The comb is a better calibrator („optical ruler“), because it features more and equally spaced emission lines than the Neon lamp.

Science contacts:

Dr. Jose Chavez-Boggio, jboggio@aip.de, +49 331-7499 665 / Dr. Andreas Kelz, akelz@aip.de, +49 331-7499 640

Media contact: Kerstin Mork, presse@aip.de, +49 331-7499 469

The key topics of the Leibniz Institute for Astrophysics Potsdam (AIP) are cosmic magnetic fields and extragalactic astrophysics. A considerable part of the institute's efforts aim at the development of research technology in the fields of spectroscopy, robotic telescopes, and e-science. The AIP is the successor of the Berlin Observatory founded in 1700 and of the Astrophysical Observatory of Potsdam founded in 1874. The latter was the world's first observatory to emphasize explicitly the research area of astrophysics. Since 1992 the AIP is a member of the Leibniz Association.

The horizontal Reynolds stress in theory (blue line) and observation (the insert).

## The Lambda effect confirmed

2 December 2014. Solar turbulence theory confirmed by solar observations: the Lambda effect exists. AIP theoreticians have long believed that turbulence on the Sun behaves opposite to what is know...

New computations of the horizontal Reynolds stress of the plasma in the (rotating) solar convection zone show it to be negative on the surface but positive in the bulk of the convection zone of the northern hemisphere (and opposite in the southern hemisphere). This is exactly what was discovered last year by the Helioseismic and Magnetic Imager onboard the Solar Dynamics Observatory (SDO).

The observed acceleration on the solar surface equator, commonly known as differential rotation, is generally believed to be produced by rotating turbulent convection, albeit the details of the physics behind it are very complex and yet to be fully understood. One of the problems was that such turbulences on the Sun appear to behave opposite to the turbulences in classical experimental physics. After Boussinesq (1897), all commonly known turbulence fields transport angular momentum towards the location of the slowest rotation rate. The Sun seems to violate this law and does it exactly in the opposite way. If indeed the solar turbulence is of non-Boussinesq type then all solar-type stars should possess accelerated equators with - as the AIP model calculations show -  very similar lap-times, i.e. the time the equator finishes one rotation more than the poles. This was also recently shown to be the case by other space missions.

The formal reason for the non-Boussinesq character of solar (and likely also stellar) turbulence is the existence of the Lambda effect which dominates the angular momentum transport if the turbulence cells are huge and long-living (of the order of the solar rotation period). Numerical experiments showed that such huge cells transport angular momentum even for rigid rotation. Just recently, the Helioseismic and Magnetic Imager on board of the Solar Dynamic Observatory detected these giant solar turbulence cells with characteristic length scales of 100,000 km. And they indeed transport the angular momentum from the slow solar poles to the fast solar equator, i.e. opposite to the Boussinesq law. This finding represents the yet best evidence for the existence of the Lambda effect, which describes the angular momentum transport of rigidly rotating anisotropic turbulence, and thus improves our overall understanding of the basic phenomenon of plasma turbulence.

Publication:  G. Rüdiger, M. Küker, & I. Tereshin 2014, “The existence of the Lambda effect in the solar convection zone as indicated by SDO/HMI data”, Astronomy & Astrophysics Letters, Volume 572, December 2014.

Science Contact: Prof. Dr. G. Rüdiger, gruediger@aip.de.

The key topics of the Leibniz Institute for Astrophysics Potsdam (AIP) are cosmic magnetic fields and extragalactic astrophysics. A considerable part of the institute's efforts aim at the development of research technology in the fields of spectroscopy, robotic telescopes, and e-science. The AIP is the successor of the Berlin Observatory founded in 1700 and of the Astrophysical Observatory of Potsdam founded in 1874. The latter was the world's first observatory to emphasize explicitly the research area of astrophysics. Since 1992 the AIP is a member of the Leibniz Association.