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arXiv · 1202.0686

Discovery of a stripped red giant core in a bright eclipsing binary star

P. F. L. Maxted·D. R. Anderson·M. R. Burleigh·A. Collier-Cameron·U. Heber·B. T. Gänsicke·S. Geier·T. Kupfer·T. R. Marsh·G. Nelemans·S. J. O'Toole·R. H. Østensen·B. Smalley·R. G. West·S. Bloemen
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Abstract

We report the serendipitous discovery from WASP archive photometry of a binary star in which an apparently normal A-type star (J0247-25A) eclipses a smaller, hotter subdwarf star (J0247-25B). The kinematics of J0247-25A 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 J0247-25B assuming that J0247-25A has the mass appropriate for a normal thick-disk star. We find that the properties of J0247-25B 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, J0247-25B will go on to become a low mass white dwarf (M~0.25 solar masses) composed mostly of helium. J0247-25B 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 J0247-25A 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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P. F. L. Maxted, D. R. Anderson, M. R. Burleigh, A. Collier-Cameron, U. Heber, B. T. Gänsicke, S. Geier, T. Kupfer, T. R. Marsh, G. Nelemans, S. J. O'Toole, R. H. Østensen, B. Smalley, R. G. West, S. Bloemen. 2012-02-03. Discovery of a stripped red giant core in a bright eclipsing binary star. https://arxiv.org/abs/1202.0686

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