We have identified a star in the WASP archive photometry with an unusual lightcurve due to the total eclipse of a small, hot star by an apparently normal A-type star and with an orbital period of only 0.668d. From an analysis of the WASP lightcurve together with V-band and I_C-band photometry of the eclipse and a spectroscopic orbit for the A-type star we estimate that the companion star has a mass of (0.23+-0.03)Msun and a radius of (0.33+-0.01)Rsun, assuming that the A-type star is a main-sequence star with the metalicity appropriate for a thick-disk star. The effective temperature of the companion is (13400+-1200)K from which we infer a luminosity of (3+-1)Lsun. From a comparison of these parameters to various models we conclude that the companion is most likely to be the remnant of a red giant star that has been very recently stripped of its outer layers by mass transfer onto the A-type star. In this scenario, the companion is currently in a shell hydrogen-burning phase of its evolution, evolving at nearly constant luminosity to hotter effective temperatures prior to ceasing hydrogen burning and fading to become a low-mass white dwarf composed of helium (He-WD). The system will then resemble the pre-He-WD/He-WD companions to A-type and B-type stars recently identified from their Kepler satellite lightcurves (KOI-74, KOI-81 and KIC10657664). This newly discovered binary offers the opportunity to study the evolution of a stripped red giant star through the pre-He-WD stage in great detail.
@article{arxiv.1107.4986,
title = {Discovery of a stripped red giant core in a bright eclipsing binary system},
author = {P. F. L. Maxted and D. R. Anderson and M. R. Burleigh and A. Collier-Cameron and U. Heber and B. T. Gaensicke and S. Geier and T. Kupfer and T. R. Marsh and G. Nelemans and S. J. O'Toole and R. H. Ostensen and B. Smalley and R. G. West},
journal= {arXiv preprint arXiv:1107.4986},
year = {2015}
}
Comments
Accepted (subject to minor revision) for publication in MNRAS. This is the re-submitted revised version