# News

## Solar eclipse seen by the LOFAR RadioTelescope

23 March 2015. The European radio interferometer LOFAR succeeded in taking unique pictures of the solar eclipse on March 20th as it is not possible by eye.

In the movie the path of the Moon’s shadow over the Sun is seen. The video shows the Sun at a frequency range of 115-175 MHz, which corresponds to a wavelength of about two meters. The radio emission originates from the Sun's outer atmosphere, the corona. This radiation is enhanced over active regions, where Sunspots are seen and strong magnetic fields dominate. These regions can be the source of solar eruptions. The eye-catching bright spot in the upper left of the picture marks such a region of high activity and is visible as a dark Sunspot at optical wavelengths.

Gottfried Mann from the Leibniz Institute for Astrophysics Potsdam (AIP) coordinates the solar observations with the LOw Frequency ARray (LOFAR). The solar eclipse was observed to gain specific information on the structure of the solar atmosphere. Christian Vocks, PI of the observations on March 20,  explains: „Radio waves pass without problem through clouds in the Earth’s atmosphere, so that observations do not depend on weather.“ Still, the image of the Sun appears nebulous because: „Observations of the Sun through the Earth’s atmosphere with a radio telescope suffer from the same effect like if you try to take pictures from the bottom of a swimming pool.“

Click on picture above to start video.

The now published movie is based on data gathered with the International LOFAR telescope (ILT). The Leibniz Institute for Astrophysics Potsdam (AIP) operates one of LOFAR's stations in Potsdam Bornim.

LOFAR is the Low Frequency Array designed and constructed by ASTRON. It has facilities in several countries, that are owned by various parties (each with their own funding sources), and that are collectively operated by the ILT foundation under a joint scientific policy. LOFAR is well suited for a wide variety of scientific topics, from the early universe to Earth's space environment

Science contact:

Apl. Prof. Dr. Gottfried Mann, gmann@aip.de, +49 331 7499 292

Dr. Christian Vocks, cvocks@aip.de, +49 331 7499 327

## ESO: 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.