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Hohle M.M.,Astrophysical Institute and University Observatory Jena | Hohle M.M.,Max Planck Institute for Extraterrestrial Physics | Neuhauser R.,Astrophysical Institute and University Observatory Jena | Schutz B.F.,Max Planck Institute for Physics | Schutz B.F.,University of Cardiff
Astronomische Nachrichten | Year: 2010

Massive stars are of interest as progenitors of supernovae, i.e. neutron stars and black holes, which can be sources of gravitational waves. Recent population synthesis models can predict neutron star and gravitational wave observations but deal with a fixed supernova rate or an assumed initial mass function for the population of massive stars. Here we investigate those massive stars, which are supernova progenitors, i.e. with O- and early B-type stars, and also all supergiants within 3 kpc. We restrict our sample to those massive stars detected both in 2MASS and observed by Hipparcos, i.e. only those stars with parallax and precise photometry. To determine the luminosities we calculated the extinctions from published multi-colour photometry, spectral types, luminosity class, all corrected for multiplicity and recently revised Hipparcos distances. We use luminosities and temperatures to estimate the masses and ages of these stars using different models from different authors. Having estimated the luminosities of all our stars within 3 kpc, in particular for all O- and early B-type stars, we have determined the median and mean luminosities for all spectral types for luminosity classes I, III, and V. Our luminosity values for supergiants deviate from earlier results: Previous work generally overestimates distances and luminosities compared to our data, this is likely due to Hipparcos parallaxes (generally more accurate and larger than previous ground-based data) and the fact that many massive stars have recently been resolved into multiples of lower masses and luminosities. From luminosities and effective temperatures we derived masses and ages using mass tracks and isochrones from different authors. From masses and ages we estimated lifetimes and derived a lower limit for the supernova rate of ≈20 events/Myr averaged over the next 10 Myr within 600 pc from the sun. These data are then used to search for areas in the sky with higher likelihood for a supernova or gravitational wave event (like OB associations). © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source


Seeliger M.,Astrophysical Institute and University Observatory Jena | Kitze M.,Astrophysical Institute and University Observatory Jena | Errmann R.,Astrophysical Institute and University Observatory Jena | Errmann R.,Friedrich - Schiller University of Jena | And 50 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2015

As part of our ongoing effort to investigate transit timing variations (TTVs) of known exoplanets, we monitored transits of the four exoplanets HAT-P-18b, HAT-P-19b, HAT-P-27b/WASP-40b and WASP-21b. All of them are suspected to show TTVs due to the known properties of their host systems based on the respective discovery papers. During the past three years 46 transit observations were carried out, mostly using telescopes of the Young Exoplanet Transit Initiative. The analyses are used to refine the systems' orbital parameters. In all cases we found no hints for significant TTVs, or changes in the system parameters inclination, fractional stellar radius and planet-to-star radius ratio. However, comparing our results with those available in the literature shows that we can confirm the already published values. © 2015 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. Source


Seeliger M.,Astrophysical Institute and University Observatory Jena | Dimitrov D.,Bulgarian Academy of Science | Kjurkchieva D.,University of Shumen | Mallonn M.,Leibnitz Institute For Astrophysik Potsdam | And 26 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2014

We present the results of 45 transit observations obtained for the transiting exoplanet HAT-P-32b. The transits have been observed using several telescopes mainly throughout the YETI (Young Exoplanet Transit Initiative) network. In 25 cases, complete transit light curves with a timing precision better than 1.4 min have been obtained. These light curves have been used to refine the system properties, namely inclination i, planet-to-star radius ratio Rp/Rs, and the ratio between the semimajor axis and the stellar radius a/Rs. First analyses by Hartman et al. suggests the existence of a second planet in the system, thus we tried to find an additional body using the transit timing variation (TTV) technique. Taking also the literature data points into account, we can explain all mid-transit times by refining the linear ephemeris by 21 ms. Thus, we can exclude TTV amplitudes of more than ~1.5 min. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. Source

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