Browsing by Author "Kilkenny, Dave"

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    Hot white dwarfs and pre-white dwarfs discovered with SALT
    (Oxford University Press, 2023) Jeffery, C. Simon; Werner, K.; Kilkenny, Dave
    The Southern African Large Telescope survey of helium-rich hot subdwarfs aims to explore evolutionary pathways among groups of highly evolved stars. The selection criteria mean that several hot white dwarfs and related objects have also been included. This paper reports the discovery and analysis of eight new very hot white dwarf and pre-white dwarf stars with effective temperatures exceeding 100 000 K. They include two PG1159 stars, one DO white dwarf, three O(He), and two O(H) stars.
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    News from the EREBOS project
    (De Gruyter Open, 2017) Schaffenroth, Veronika; Barlow, Brad; Geier, Stephan; Vučković, Maja; Kilkenny, Dave; Schaffenroth, Johannes
    Planets and brown dwarfs in close orbits will interact with their host stars, as soon as the stars evolve to become red giants. However, the outcome of those interactions is still unclear. Recently, several brown dwarfs have been discovered orbiting hot subdwarf stars at very short orbital periods of 0.065 - 0.096 d. More than 8% of the close hot subdwarf binaries might have sub-stellar companions. This shows that such companions can significantly affect late stellar evolution and that sdB binaries are ideal objects to study this influence. Thirty-eight new eclipsing sdB binary systems with cool low-mass companions and periods from 0.05 to 0.5 d were discovered based on their light curves by the OGLE project. In the recently published catalog of eclipsing binaries in the Galactic bulge, we discovered 75 more systems. We want to use this unique and homogeneously selected sample to derive the mass distribution of the companions, constrain the fraction of sub-stellar companions and determine the minimum mass needed to strip off the red-giant envelope. We are especially interested in testing models that predict hot Jupiter planets as possible companions. Therefore, we started the EREBOS (Eclipsing Reflection Effect Binaries from the OGLE Survey) project, which aims at analyzing those new HW Vir systems based on a spectroscopic and photometric follow up. For this we were granted an ESO Large Program for ESO-VLT/FORS2. Here we give an update on the the current status of the project and present some preliminary results.
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    The orbital periods of aa dor and ny vir
    (Oxford University Press, 2011) Kilkenny, Dave
    New timings of eclipses made between 2000 and 2010 are presented for two binary systems with hot subdwarf primary stars. In the case of AA Dor, an sdOB star with a very cool secondary, the period is found to be constant at a level of about 10−14 d per orbit. In the case of NY Vir, a rapidly pulsating sdBVr with a cool companion, the period is discovered to be decreasing at a rate of −11.2 × 10−13 d per orbit. Close binary stars are particularly useful for the determination of fundamental stellar parameters. Double-lined spectroscopic binaries enable the mass ratio of the binary components to be determined and, if the inclination of the binary orbit can be measured or reasonably constrained (as in the case of an eclipsing system), then the absolute masses can be found. In addition, the light curve of an eclipsing system allows relative stellar radii to be found and even the absolute radii if the system is a double-lined binary.
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    A search for variable subdwarf B stars in TESS Full Frame Images III. An update on variable targets in both ecliptic hemispheres – contamination analysis and new sdB pulsators
    (Oxford University Press, 2023) Sahoo, Sumanta Kumar; Baran, Andrzej; Kilkenny, Dave
    We present an update on the variable star survey performed on the TESS 30 min Full Frame Image (FFI) data reported by our first two papers in this series. This update includes a contamination analysis in order to identify false positives and analysis of the TESS 10 min FFI data collected during Years 3 and 4 of the mission. We clarify the variability status of 2 995 targets identifying 1 403 variable stars. In addition, we spectroscopically classify 24 prefiltered targets sampled with the 10 min FFI data and discover 11 new sdB pulsators. Future follow-up space- and/or ground-based data of variables reported here, to identify the nature of their variability and reveal spectroscopic parameters of the stars, would complement this work.