Institute For Astrophysik Gottingen

Göttingen, Germany

Institute For Astrophysik Gottingen

Göttingen, Germany
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Hill G.J.,University of Texas at Austin | Tuttle S.E.,University of Texas at Austin | Drory N.,University of Texas at Austin | Lee H.,University of Texas at Austin | And 28 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2014

The Visible Integral-field Replicable Unit Spectrograph (VIRUS) consists of a baseline build of 150 identical spectrographs (arrayed as 75 unit pairs) fed by 33,600 fibers, each 1.5 arcsec diameter, at the focus of the upgraded 10 m Hobby-Eberly Telescope (HET). VIRUS has a fixed bandpass of 350-550 nm and resolving power R∼700. VIRUS is the first example of industrial-scale replication applied to optical astronomy and is capable of surveying large areas of sky, spectrally. The VIRUS concept offers significant savings of engineering effort, cost, and schedule when compared to traditional instruments. The main motivator for VIRUS is to map the evolution of dark energy for the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX), using 0.8M Lyman-α emitting galaxies as tracers. The full VIRUS array is due to be deployed starting at the end of 2014 and will provide a powerful new facility instrument for the HET, well suited to the survey niche of the telescope, and will open up large area surveys of the emission line universe for the first time. VIRUS is in full production, and we are about half way through. We review the production design, lessons learned in reaching volume production, and preparation for deployment of this massive instrument. We also discuss the application of the replicated spectrograph concept to next generation instrumentation on ELTs. © 2014 SPIE.

Van Boekel R.,Max Planck Institute for Astronomy | Benneke B.,Massachusetts Institute of Technology | Heng K.,ETH Zurich | Hu R.,Massachusetts Institute of Technology | And 31 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2012

We present EclipseSim, a radiometric model for exoplanet transit spectroscopy that allows easy exploration of the fundamental performance limits of any space-based facility aiming to perform such observations. It includes a library of stellar model atmosphere spectra and can either approximate exoplanet spectra by simplified models, or use any theoretical or observed spectrum, to simulate observations. All calculations are done in a spectrally resolved fashion and the contributions of the various fundamental noise sources are budgeted separately, allowing easy assessment of the dominant noise sources, as a function of wavelength. We apply EclipseSimto the Exoplanet Characterization Observatory (EChO), a proposed mission dedicated to exoplanet transit spectroscopy that is currently in competition for the M3 launch slot of ESA's cosmic vision programme. We show several case studies on planets with sizes in the super-Earth to Jupiter range, and temperatures ranging from the temperate to the ≈1500K regime, demonstrating the power and versatility of EChO. EclipseSim is publicly available. © 2012 SPIE.

Bellinger E.P.,Max Planck Institute for Solar System Research | Bellinger E.P.,University of Aarhus | Bellinger E.P.,University of Gottingen | Angelou G.C.,Max Planck Institute for Solar System Research | And 7 more authors.
Astrophysical Journal | Year: 2016

Owing to the remarkable photometric precision of space observatories like Kepler, stellar and planetary systems beyond our own are now being characterized en masse for the first time. These characterizations are pivotal for endeavors such as searching for Earth-like planets and solar twins, understanding the mechanisms that govern stellar evolution, and tracing the dynamics of our Galaxy. The volume of data that is becoming available, however, brings with it the need to process this information accurately and rapidly. While existing methods can constrain fundamental stellar parameters such as ages, masses, and radii from these observations, they require substantial computational effort to do so. We develop a method based on machine learning for rapidly estimating fundamental parameters of main-sequence solar-like stars from classical and asteroseismic observations. We first demonstrate this method on a hare-and-hound exercise and then apply it to the Sun, 16 Cyg A and B, and 34 planet-hosting candidates that have been observed by the Kepler spacecraft. We find that our estimates and their associated uncertainties are comparable to the results of other methods, but with the additional benefit of being able to explore many more stellar parameters while using much less computation time. We furthermore use this method to present evidence for an empirical diffusion-mass relation. Our method is open source and freely available for the community to use.6 © 2016. The American Astronomical Society. All rights reserved.

Von Essen C.,University of Aarhus | Von Essen C.,Institute For Astrophysik Gottingen | Mallonn M.,Leibniz Institute for Astrophysics Potsdam | Albrecht S.,University of Aarhus | And 4 more authors.
Astronomy and Astrophysics | Year: 2015

We observed a secondary eclipse of WASP-33 b quasi-simultaneously in the optical (∼0.55 μm) and the near-infrared (∼1.05 μm) using the 2 × 8.4 m Large Binocular Telescope. WASP-33 is a δ Scuti star pulsating with periods comparable to the eclipse duration, making the determination of the eclipse depth challenging. We use previously determined oscillation frequencies to model and remove the pulsation signal from the light curves, isolating the secondary eclipse. The determined eclipse depth is ΔF = 1.03 ± 0.34 parts per thousand, corresponding to a brightness temperature of TB = 3398 ± 302 K. Combining previously published data with our new measurement we find the equilibrium temperature of WASP-33 b to be TB = 3358 ± 165 K. We compare all existing eclipse data to a blackbody spectrum, to a carbon-rich non-inverted model and to a solar composition model with an inverted temperature structure. We find that current available data on WASP-33 b's atmosphere can be best represented by a simple blackbody emission, without the need for more sophisticated atmospheric models with temperature inversions. Although our data cannot rule out models with or without a temperature inversion, they do confirm a high brightness temperature for the planet at short wavelengths. WASP-33 b is one of the hottest exoplanets known till date, and its equilibrium temperature is consistent with rapid reradiation of the absorbed stellar light and a low albedo. © ESO, 2015.

Volkmer R.,Kiepenheuer Institute for Solar Physics | Von Der Luhe O.,Kiepenheuer Institute for Solar Physics | Denker C.,Leibniz Institute for Astrophysics Potsdam | Solanki S.,Max Planck Institute for Solar System Research | And 16 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2010

With the integration of a 1-meter Cesic primary mirror the GREGOR telescope pre-commissioning started. This is the first time, that the entire light path has seen sunlight. The pre-commissioning period includes testing of the main optics, adaptive optics, cooling system, and pointing system. This time was also used to install a near-infrared grating spectro-polarimeter and a 2D-spectropolarimeter for the visible range as first-light science instruments. As soon as the final 1.5 meter primary mirror is installed, commissioning will be completed, and an extended phase of science verification will follow. In the near future, GREGOR will be equipped with a multi-conjugate adaptive optics system that is presently under development at KIS. © 2010 SPIE.

Royer F.,CNRS Galaxies, Stars, Physics and Instrumentation Laboratory | Gebran M.,Notre Dame University - Louaize | Monier R.,University Pierre and Marie Curie | Monier R.,University of Nice Sophia Antipolis | And 7 more authors.
Astronomy and Astrophysics | Year: 2014

Context. The study of rotational velocity distributions for normal stars requires an accurate spectral characterization of the objects in order to avoid polluting the results with undetected binary or peculiar stars. This piece of information is a key issue in the understanding of the link between rotation and the presence of chemical peculiarities. Aims. A sample of 47 low vsini A0-A1 stars (vsini < 65 km s-1), initially selected as main-sequence normal stars, are investigated with high-resolution and high signal-to-noise spectroscopic data. The aim is to detect spectroscopic binaries and chemically peculiar stars, and eventually establish a list of confirmed normal stars. Methods. A detailed abundance analysis and spectral synthesis is performed to derive abundances for 14 chemical species. A hierarchical classification, taking measurement errors into account, is applied to the abundance space and splits the sample into two different groups, identified as the chemically peculiar stars and the normal stars. Results. We show that about one third of the sample is actually composed of spectroscopic binaries (12 double-lined and five single-lined spectroscopic binaries). The hierarchical classification breaks down the remaining sample into 13 chemically peculiar stars (or uncertain) and 17 normal stars. © ESO, 2014.

Schleicher D.R.G.,University of Concepción | Schleicher D.R.G.,Institute For Astrophysik Gottingen | Dreizler S.,Institute For Astrophysik Gottingen | Volschow M.,Hamburg Observatory | And 2 more authors.
Astronomische Nachrichten | Year: 2015

To understand the evolution of planetary systems, it is important to investigate planets in highly evolved stellar systems, and to explore the implications of their observed properties with respect to potential formation scenarios. Observations suggest the presence of giant planets in post-common-envelope binaries (PCEBs). A particularly well-studied system with planetary masses of 1.7 MJ and 7.0 MJ is NN Ser. We show here that a pure first-generation scenario where the planets form before the common envelope (CE) phase and the orbits evolve due to the changes in the gravitational potential is inconsistent with the current data. We propose a second-generation scenario where the planets are formed from the material that is ejected during the CE, which may naturally explain the observed planetary masses. In addition, hybrid scenarios where the planets form before the CE and evolve due to the accretion of the ejected gas appear as a realistic possibility. Copyright © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Panesar N.K.,Max Planck Institute for Solar System Research | Panesar N.K.,Institute For Astrophysik Gottingen | Innes D.E.,Max Planck Institute for Solar System Research | Schmit D.J.,Max Planck Institute for Solar System Research | And 2 more authors.
Solar Physics | Year: 2014

Polar crown prominences, that partially circle the Sun's poles between 60° and 70° latitude, are made of chromospheric plasma. We aim to diagnose the 3D dynamics of a polar crown prominence using high-cadence EUV images from the Solar Dynamics Observatory (SDO)/AIA at 304, 171, and 193 Å and the Ahead spacecraft of the Solar Terrestrial Relations Observatory (STEREO-A)/EUVI at 195 Å. Using time series across specific structures, we compare flows across the disk in 195 Å with the prominence dynamics seen on the limb. The densest prominence material forms vertical columns that are separated by many tens of Mm and connected by dynamic bridges of plasma that are clearly visible in 304/171 Å two-colour images. We also observe intermittent but repetitious flows with velocity 15 km s-1 in the prominence that appear to be associated with EUV bright points on the solar disk. The boundary between the prominence and the overlying cavity appears as a sharp edge. We discuss the structure of the coronal cavity seen both above and around the prominence. SDO/HMI and GONG magnetograms are used to infer the underlying magnetic topology. The evolution and structure of the prominence with respect to the magnetic field seems to agree with the filament-linkage model. © 2014 Springer Science+Business Media Dordrecht.

Reiners A.,Institute For Astrophysik Gottingen | Joshi N.,Institute For Astrophysik Gottingen | Goldman B.,Max Planck Institute for Astronomy
Astronomical Journal | Year: 2012

We present a catalog of rotation and chromospheric activity in a sample of 334 Mdwarfs of spectral types M0-M4.5 populating the parameter space around the boundary to full convection. We obtain high-resolution optical spectra for 206 targets and determine projected rotational velocity, vsin i, and Hα emission. The data are combined with measurements of vsin i in field stars of the same spectral type from the literature. Our sample adds 157 new rotation measurements to the existing literature and almost doubles the sample of available vsin i. The final sample provides a statistically meaningful picture of rotation and activity at the transition to full convection in the solar neighborhood. We confirm a steep rise in the fraction of active stars at the transition to full convection known from earlier work. In addition, we see a clear rise in rotational velocity in the same stars. In very few stars, no chromospheric activity but a detection of rotational broadening is reported. We argue that all of them are probably spurious detections; we conclude that in our sample all significantly rotating stars are active, and all active stars are significantly rotating. The rotation-activity relation is valid in partially and in fully convective stars. Thus, we do not observe any evidence for a transition from a rotationally dominated dynamo in partially convective stars to a rotation-independent turbulent dynamo in fully convective stars; turbulent dynamos in fully convective stars of spectral types around M4 are still driven by rotation. Finally, we compare projected rotational velocities of 33stars to rotational periods derived from photometry in the literature and determine inclinations for a few of them. © 2012. The American Astronomical Society. All rights reserved.

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