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Tautenburg, Germany

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.

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.

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.

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.

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

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