Thuringer Landessternwarte

Tautenburg, Germany

Thuringer Landessternwarte

Tautenburg, Germany

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Sale S.E.,Rudolf Peierls Center for Theoretical Physics | Drew J.E.,University of Hertfordshire | Barentsen G.,University of Hertfordshire | Farnhill H.J.,University of Hertfordshire | And 7 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2014

We present a 3D map of extinction in the northern Galactic plane derived using photometry from the INT/WFC Photometric Hα Survey of the northern Galactic plane. The map has fine angular (~10 arcmin) and distance (100 pc) sampling allied to a significant depth (≳5 kpc). We construct the map using a method based on a hierarchical Bayesian model described in a previous article by Sale. In addition to mean extinction, we also measure differential extinction, which arises from the fractal nature of the interstellar medium, and show that it will be the dominant source of uncertainty in estimates of extinction to some arbitrary position. The method applied also furnishes us with photometric estimates of the distance, extinction, effective temperature, surface gravity, and mass for ~38 million stars. Both the extinction map and the catalogue of stellar parameters are made publicly available via http://www.iphas.org/extinction. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Nuza S.E.,Leibniz Institute for Astrophysics Potsdam | Hoeft M.,Thuringer Landessternwarte | van Weeren R.J.,Leiden University | Gottlober S.,Leibniz Institute for Astrophysics Potsdam | Yepes G.,Autonomous University of Madrid
Monthly Notices of the Royal Astronomical Society | Year: 2012

Upcoming radio telescopes will allow us to study the radio sky at low frequencies with unprecedented sensitivity and resolution. New surveys are expected to discover a large number of new radio sources, in particular those with a steep radio spectrum. Here we investigate the abundance of radio relics, i.e. steep-spectrum diffuse radio emission coming from the periphery of galaxy clusters, which is believed to trace shock waves induced by cluster mergers. With the advent of comprehensive relic samples, a framework is needed to analyse the relic abundance statistically. To this end, we introduce the probability of finding a relic located in a galaxy cluster with given mass and redshift, which allows us to relate the halo mass function of the Universe to radio-relic number counts. To date, about 45 relics have been reported in the literature and we compile the resulting counts, N(>S1.4). In principle, the parameters of the distribution could be determined using a sufficiently large relic sample. However, since the number of known relics is still small, for that purpose we use the MareNostrum Universe simulation to determine the relic radio-power scaling with cluster mass and redshift. Our model is able to reproduce the recently found tentative evidence for an increase in the fraction of clusters hosting relics, both with X-ray luminosity and redshift, using an X-ray flux-limited cluster sample. Moreover, we find that a considerable fraction of faint relics (S1.4≲ 10 mJy) reside in clusters with an X-ray flux below ≲ 3 × 10-12 erg s-1 cm-2. Finally, we estimate the number of radio relics that await discovery by future low-frequency surveys proposed for the Low Frequency Array (LOFAR) and the Westerbork Synthesis Radio Telescope (WSRT). We estimate that the Westerbork Observations of the Deep APERTIF Northern-Sky (WODAN) survey proposed for WSRT may discover 900 relics and that the LOFAR-Tier 1-120MHz survey may discover about 2500 relics. However, the actual number of newly discovered relics will depend crucially on the existence of sufficiently complete galaxy cluster catalogues. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.


Ogrean G.A.,Hamburger Sternwarte | Bruggen M.,Hamburger Sternwarte | van Weeren R.J.,Harvard - Smithsonian Center for Astrophysics | Rottgering H.,Leiden University | And 2 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2013

The cluster 1RXS J0603.3+4214 is a merging galaxy cluster that hosts three radio relics and agiant radio halo. The northern relic, the Toothbrush, is 1.9 Mpc long and has an unusual linearmorphology. According to simple diffusive shock acceleration theory, its radio spectral indexindicates a Mach number of 3.3-4.6. Here, we present results from a deep XMM-Newtonobservation of the cluster. We observe two distinct cluster cores that have survived the merger. The presence of three shocks at or near the locations of the radio relics is confirmed bydensity and temperature discontinuities. However, the observation poses several puzzles thatchallenge our understanding of radio relics: (i) at the Toothbrush, the shock Mach numberis not larger than 2, in apparent conflict with the shock strength predicted from the radiospectrum; (ii) at the Toothbrush, the shock front is, in part, spatially offset from the radioemission; (iii) at the eastern relic, we detect a temperature jump corresponding to a Machnumber of approximately 2.5, but there is no associated surface brightness discontinuity. Wediscuss possible explanations for these findings. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Cabrera J.,German Aerospace Center | Csizmadia Sz.,German Aerospace Center | Lehmann H.,Thuringer Landessternwarte | Dvorak R.,Universitatssternwarte Wien | And 8 more authors.
Astrophysical Journal | Year: 2014

We announce the discovery of a planetary system with seven transiting planets around a Kepler target, a current record for transiting systems. Planets b, c, e, and f are reported for the first time in this work. Planets d, g, and h were previously reported in the literature, although here we revise their orbital parameters and validate their planetary nature. Planets h and g are gas giants and show strong dynamical interactions. The orbit of planet g is perturbed in such a way that its orbital period changes by 25.7 hr between two consecutive transits during the length of the observations, which is the largest such perturbation found so far. The rest of the planets also show mutual interactions: planets d, e, and f are super-Earths close to a mean motion resonance chain (2:3:4), and planets b and c, with sizes below 2 Earth radii, are within 0.5% of the 4:5 mean motion resonance. This complex system presents some similarities to our solar system, with small planets in inner orbits and gas giants in outer orbits. It is, however, more compact. The outer planet has an orbital distance around 1 AU, and the relative position of the gas giants is opposite to that of Jupiter and Saturn, which is closer to the expected result of planet formation theories. The dynamical interactions between planets are also much richer. © 2014. The American Astronomical Society. All rights reserved.


McArthur B.E.,University of Texas at Austin | Benedict G.F.,University of Texas at Austin | Henry G.W.,Tennessee State University | Hatzes A.,Thuringer Landessternwarte | And 4 more authors.
Astrophysical Journal | Year: 2014

We have used high-cadence radial velocity measurements from the Hobby-Eberly Telescope with published velocities from the Lick 3 m Shane Telescope, combined with astrometric data from the Hubble Space Telescope (HST) Fine Guidance Sensors to refine the orbital parameters of the HD 128311 system, and determine an inclination of 55.°95 ± 14.°55 and true mass of 3.789 M JUP for HD 128311 c. The combined radial velocity data also reveal a short period signal which could indicate a third planet in the system with an Msin i of 0.133 ± 0.005 M JUP or stellar phenomena. Photometry from the T12 0.8 m automatic photometric telescope at the Fairborn Observatory and HST are used to determine a photometric period close to, but not within the errors of the radial velocity signal. We performed a cross-correlation bisector analysis of the radial velocity data to look for correlations with the photometric period and found none. Dynamical integrations of the proposed system show long-term stability with the new orbital parameters of over 10 million years. Our new orbital elements do not support the claims of HD 128311 b and c being in mean motion resonance. © 2014. The American Astronomical Society. All rights reserved..


Araya-Melo P.A.,Jacobs University Bremen | Aragon-Calvo M.A.,Johns Hopkins University | Bruggen M.,Jacobs University Bremen | Hoeft M.,Thuringer Landessternwarte
Monthly Notices of the Royal Astronomical Society | Year: 2012

We explore the possibility of detecting radio emission in the cosmic web by analysing shock waves in the MareNostrum cosmological simulation. This requires a careful calibration of shock finding algorithms in smoothed particle hydrodynamics simulations, which we present here. Moreover, we identify the elements of the cosmic web, namely voids, walls, filaments and clusters with the use of the SpineWeb technique, a procedure that classifies the structure in terms of its topology. Thus, we are able to study the Mach number distribution as a function of its environment. We find that the median Mach number for clusters is , for filaments is , for walls is and for voids is We then estimate the radio emission in the cosmic web using the formalism derived in Hoeft & Brüggen. We also find that in order to match our simulations with observational data [e.g. NRAO VLA Sky Survey (NVSS) radio relic luminosity function], a fraction of energy dissipated at the shock of ξe= 0.0005 is needed, in contrast with the ξe= 0.005 proposed by Hoeft et al. We find that 41 percent of clusters with M≥ 1014M⊙ host diffuse radio emission in the form of radio relics. Moreover, we predict that the radio flux from filaments should be Jy at a frequency of 150 MHz. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.


Ofir A.,Tel Aviv University | Gandolfi D.,European Space Agency | Buchhave L.,Copenhagen University | Lacy C.H.S.,University of Arkansas | And 2 more authors.
Monthly Notices of the Royal Astronomical Society: Letters | Year: 2012

KIC 1571511 is a 14-d eclipsing binary (EB) in the Kepler data set. The secondary of this EB is a very low mass star with amass of 0.14136±0.00036M⊙ and a radius of 0.17831+0.00051 -0.00062 R⊙ (statistical errors only). The overall system parameters make KIC 1571511B an ideal benchmark object: among the smallest, lightest and best-described stars known, smaller even than some known exoplanet. Currently available photometry encompasses only a small part of the total: future Kepler data releases promise to constrain many of the properties of KIC 1571511B to unprecedented level. However, as in many spectroscopic single-lined systems, the current error budget is dominated by the modelling errors of the primary and not by the above statistical errors. We conclude that detecting the RV signal of the secondary component is crucial to achieving the full potential of this possible benchmark object for the study of low-mass stars. © 2012 The Authors. Monthly Notices of the Royal Astronomical Society. © 2012 RAS.


Hatzes A.P.,Thuringer Landessternwarte
Space Science Reviews | Year: 2016

Prior to the discovery of exoplanets our expectations of their architecture were largely driven by the properties of our solar system. We expected giant planets to lie in the outer regions and rocky planets in the inner regions. Planets should probably only occupy orbital distances 0.3–30 AU from the star. Planetary orbits should be circular, prograde and in the same plane. The reality of exoplanets have shattered these expectations. Jupiter-mass, Neptune-mass, Superearths, and even Earth-mass planets can orbit within 0.05 AU of the stars, sometimes with orbital periods of less than one day. Exoplanetary orbits can be eccentric, misaligned, and even in retrograde orbits. Radial velocity surveys gave the first hints that the occurrence rate increases with decreasing mass. This was put on a firm statistical basis with the Kepler mission that clearly demonstrated that there were more Neptune- and Superearth-sized planets than Jupiter-sized planets. These are often in multiple, densely packed systems where the planets all orbit within 0.3 AU of the star, a result also suggested by radial velocity surveys. Exoplanets also exhibit diversity along the main sequence. Massive stars tend to have a higher frequency of planets ((Formula presented.)) that tend to be more massive ((Formula presented.)). Giant planets around low mass stars are rare, but these stars show an abundance of small (Neptune and Superearth) planets in multiple systems. Planet formation is also not restricted to single stars as the Kepler mission has discovered several circumbinary planets. Although we have learned much about the architecture of planets over the past 20 years, we know little about the census of small planets at relatively large ((Formula presented.)) orbital distances. We have yet to find a planetary system that is analogous to our own solar system. The question of how unique are the properties of our own solar system remains unanswered. Advancements in the detection methods of small planets over a wide range of orbital distances is needed before we gain a complete understanding of the architecture of exoplanetary systems. © 2016 Springer Science+Business Media Dordrecht


Hatzes A.P.,Thuringer Landessternwarte
Astronomische Nachrichten | Year: 2013

We investigate the radial velocity variations of GJ 581 based on measurements from the HARPS and Keck HIRES spectrographs. A Fourier pre-whitening procedure is able to extract four planetary signals in the HARPS data and two from the Keck data. Combining both data sets increases the significance of the four planet signals found by HARPS. This indicates that the Keck data also supports the presence of four planets. A periodogram analysis of the residual radial velocity measurements after removal of the four planetary signals shows several periodic signals that are significant when assessing the false alarm probability via a bootstrap. However, it is demonstrated that these are not due to planetary companions. This analysis is able to confirm the presence of four planets around GJ 581, but not the presence of GJ 581g. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Hatzes A.P.,Thuringer Landessternwarte
Astrophysical Journal | Year: 2013

We present an analysis of the publicly available HARPS radial velocity (RV) measurements for α Cen B, a star hosting an Earth-mass planet candidate in a 3.24 day orbit. The goal is to devise robust ways of extracting low-amplitude RV signals of low-mass planets in the presence of activity noise. Two approaches were used to remove the stellar activity signal which dominates the RV variations: (1) Fourier component analysis (pre-whitening), and (2) local trend filtering (LTF) of the activity using short time windows of the data. The Fourier procedure results in a signal at P = 3.236 days and K = 0.42 m s -1, which is consistent with the presence of an Earth-mass planet, but the false alarm probability for this signal is rather high at a few percent. The LTF results in no significant detection of the planet signal, although it is possible to detect a marginal planet signal with this method using a different choice of time windows and fitting functions. However, even in this case the significance of the 3.24 day signal depends on the details of how a time window containing only 10% of the data is filtered. Both methods should have detected the presence of α Cen Bb at a higher significance than is actually seen. We also investigated the influence of random noise with a standard deviation comparable to the HARPS data and sampled in the same way. The distribution of the noise peaks in the period range 2.8-3.3 days has a maximum of ≈3.2 days and amplitudes approximately one-half of the K-amplitude for the planet. The presence of the activity signal may boost the velocity amplitude of these signals to values comparable to the planet. It may be premature to attribute the 3.24 day RV variations to an Earth-mass planet. A better understanding of the noise characteristics in the RV data as well as more measurements with better sampling will be needed to confirm this exoplanet. © 2013. The American Astronomical Society. All rights reserved..

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