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Paper: Discovery of a Stripped Red-giant Core in a Bright Eclipsing Binary Star
Volume: 452, Fifth Meeting on Hot Subdwarf Stars and Related Objects
Page: 137
Authors: Maxted, P. F. L.; Anderson, D. R.; Burleigh, M. R.; Collier Cameron, A.; Heber, U.; Gänsicke, B. T.; Geier, S.; Kupfer, T.; Marsh, T. R.; Nelemans, G.; O'Toole, S. J.; Østensen, R. H.; Smalley, B.; West, R. G.; Bloemen, S.
Abstract: We report the serendipitous discovery from WASP archive photometry of a binary star in which an apparently normal A-type star (J0247–25 A) eclipses a smaller, hotter subdwarf star (J0247–25 B). The kinematics of J0247–25 A show that it is a blue-straggler member of the Galactic thick-disk. We present follow-up photometry and spectroscopy from which we derive approximate values for the mass, radius and luminosity for J0247–25 B assuming that J0247–25 A has the mass appropriate for a normal thick-disk star. We find that the properties of J0247–25 B are well matched by models for a red giant stripped of its outer layers and currently in a shell hydrogen-burning stage. In this scenario, J0247–25 B will go on to become a low mass white dwarf (M ∼ 0.25M) composed mostly of helium. J0247–25 B can be studied in much greater detail than the handful of pre helium white dwarfs (pre-He-WD) identified to-date. These results have been published by Maxted et al. (2011). We also present a preliminary analysis of more recent observations of J0247–25 with the UVES spectrograph, from which we derive much improved masses for both stars in the binary. We find that both stars are more massive than expected and that J0247–25 A rotates sub-synchronously by a factor of about 2. We also present lightcurves for 5 new eclipsing pre-He-WD subsequently identified from the WASP archive photometry, 4 of which have mass estimates for the subdwarf companion based on a pair of radial velocity measurements.
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