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Potsdam, Germany

Leibniz Institute for Astrophysics Potsdam is a German research institute. It is the successor of the Berlin Observatory founded in 1700 and of the Astrophysical Observatory Potsdam founded in 1874. The latter was the world's first observatory to emphasize explicitly the research area of astrophysics. The AIP was founded in 1992, in a re-structuring following the German Reunification.The AIP is privately funded and member of the Leibniz Association. It is located in Babelsberg in the state of Brandenburg, just west of Berlin, though the Einstein Tower solar observatory and the great refractor telescope on Telegrafenberg in Potsdam belong to the AIP. The key topics of the AIP are cosmic magnetic fields on various scales and extragalactic astrophysics. Astronomical and astrophysical fields studied at the AIP range from solar and stellar physics to stellar and galactic evolution to cosmology. The institute also develops research technology in the fields of spectroscopy and robotic telescopes. It is a partner of the Large Binocular Telescope in Arizona, has erected robotic telescopes in Tenerife and the Antarctic, develops astronomical instrumentation for large telescopes such as the VLT of the ESO. Furthermore, work on several e-Science projects are carried out at the AIP. Wikipedia.

Heller R.,Leibniz Institute for Astrophysics Potsdam
Astronomy and Astrophysics | Year: 2012

Context. Detecting massive satellites that orbit extrasolar planets has now become feasible, which led naturally to questions about the habitability of exomoons. In a previous study we presented constraints on the habitability of moons from stellar and planetary illumination as well as from tidal heating. Aims. Here I refine our model by including the effect of eclipses on the orbit-averaged illumination. I then apply an analytic approximation for the Hill stability of a satellite to identify the range of stellar and planetary masses in which moons can be habitable. Moons in low-mass stellar systems must orbit their planet very closely to remain bounded, which puts them at risk of strong tidal heating. Methods. I first describe the effect of eclipses on the stellar illumination of satellites. Then I calculate the orbit-averaged energy flux, which includes illumination from the planet and tidal heating to parametrize exomoon habitability as a function of stellar mass, planetary mass, and planet-moon orbital eccentricity. The habitability limit is defined by a scaling relation at which a moon loses its water by the runaway greenhouse process. As a working hypothesis, orbital stability is assumed if the moon's orbital period is less than 1/9 of the planet's orbital period. Results. Due to eclipses, a satellite in a close orbit can experience a reduction in orbit-averaged stellar flux by up to about 6%. The smaller the semi-major axis and the lower the inclination of the moon's orbit, the stronger the reduction. I find a lower mass limit of ≈ 0.2 M for exomoon host stars that allows a moon to receive an orbit-averaged stellar flux comparable to the Earth's, with which it can also avoid the runaway greenhouse effect. Precise estimates depend on the satellite's orbital eccentricity. Deleterious effects on exomoon habitability may occur up to ≈ 0.5 M if the satellite's eccentricity is ≥ 0.05. Conclusions. Although the traditional habitable zone lies close to low-mass stars, which allows for many transits of planet-moon binaries within a given observation cycle, resources should not be spent to trace habitable satellites around them. Gravitational perturbations by the close star, another planet, or another satellite induce eccentricities that likely make any moon uninhabitable. Estimates for individual systems require dynamical simulations that include perturbations among all bodies and tidal heating in the satellite. © 2012 ESO.

Warmuth A.,Leibniz Institute for Astrophysics Potsdam
Advances in Space Research | Year: 2010

Ten years after the first observation of large-scale wave-like coronal disturbances with the EIT instrument aboard SOHO, the most crucial questions concerning these "EIT waves" are still being debated controversially - what is their actual physical nature, and how are they launched? Possible explanations include MHD waves or shocks, launched by flares or driven by coronal mass ejections (CMEs), as well as models where coronal waves are not actually waves at all, but generated by successive "activation" of magnetic fieldlines in the framework of a CME. Here, we discuss recent observations that might help to discriminate between the different models. We focus on strong coronal wave events that do show chromospheric Moreton wave signatures. It is stressed that multiwavelength observations with high time cadence are particularly important, ideally when limb events with CME observations in the low corona are available. Such observations allow for a detailed comparison of the kinematics of the wave, the CME and the associated type II radio burst. For Moreton-associated coronal waves, we find strong evidence for the wave/shock scenario. Furthermore, we argue that EIT waves are actually generated by more than one physical process, which might explain some of the issues which have made the interpretation of these phenomena so controversial. © 2009 COSPAR.

Scholz R.-D.,Leibniz Institute for Astrophysics Potsdam
Astronomy and Astrophysics | Year: 2014

Aims. Using Wide-field Infrared Survey Explorer (WISE) data and previous optical and near-infrared sky surveys, we try to identify still missing stellar and substellar neighbours of the Sun. Methods. When checking the brightest red WISE sources for proper motions and colours expected for nearby M and L dwarfs, we also approached the thin Galactic plane. Astrometry (proper motion and parallax measurements) and the available photometry were used to obtain first estimates of the distance and type of nearby candidates. Results. We have discovered WISE J072003.20-084651.2, an object with moderately high proper motion (μ ≈ 120 mas/yr) that lies at low Galactic latitude (b = +2.3), with similar brightness (J ≈ 10.6, w2 ≈ 8.9) and colours (I-J ≈ 3.2, J-Ks ≈ 1.2, w1-w2 ≈ 0.3) as the nearest known M-type brown dwarf LP 944-20. With a photometric classification as an M9 ± 1 dwarf, its photometric distance lies in the range between about 5 and 7 pc, based on comparison with absolute magnitudes of LP 944-20 alone or of a sample of M8-L0 dwarfs. The slightly larger distance derived from our preliminary trigonometric parallax (7.0 ± 1.9 pc) may indicate a close binary nature. The new neighbour is an excellent target for planet search and low-mass star/brown dwarf studies. © 2014 ESO.

Ziegler U.,Leibniz Institute for Astrophysics Potsdam
Journal of Computational Physics | Year: 2011

This work describes a novel scheme for the equations of magnetohydrodynamics on orthogonal-curvilinear grids within a finite-volume framework. The scheme is based on a combination of central-upwind techniques for hyperbolic conservation laws and projection-evolution methods originally developed for Hamilton-Jacobi equations. The scheme is derived in semi-discrete form, and a full-fledged version is obtained by applying any stable and accurate solver for integration in time. The divergence-free condition of the magnetic field is a built-in property of the scheme by virtue of a constrained-transport ansatz for the induction equation. From the general formulation second-order accurate schemes for cylindrical grids and spherical grids are introduced in some more detail pointing out their potential importance in many applications. Special emphasis in this context is put to a treatment of the geometric axis implying severe complications because of the presence of coordinate singularities and associated grid degeneracy. An attempt to tackle these problems is presented. Numerical experiments illustrate the overall robustness and performance of the scheme for a small suite of tests. © 2010 Elsevier Inc.

Ilyin I.,Leibniz Institute for Astrophysics Potsdam
Astronomische Nachrichten | Year: 2012

Accurate measurements of Stokes IQUV in spectral lines is required for precise reconstruction of stellar magnetic field geometries with Zeeman-Dopper imaging. Spectral Zeeman features are intrinsically weak and subjected to a number of instrumental uncertainties. The aim of this work is to study the details of the instrumental uncertainties in the Stokes IQUV measurements in spectral lines and ways of their reduction. We make a practical comparison of the polarimetric performances of two high-resolution échelle spectropolarimeters, namely SOFIN at the NOT, and HARPS at ESO. We show the residual spectra for both instruments to characterize the cross-talk between the observed Stokes parameters. We employ a self-calibrating least-squares fit to eliminate some of the polarization uncertainties to derive the full Stokes vector from stellar spectra. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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