SIMBAD references

We have identified a star in the Wide Angle Search for Planets (WASP) archive photometry with an unusual light curve due to the total eclipse of a small, hot star by an apparently normal A-type star and with an orbital period of only 0.668 d. From an analysis of the WASP light curve 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 M_☉ and a radius of 0.33±0.01 R_☉, assuming that the A-type star is a main-sequence star with the metallicity appropriate for a thick-disc star. The effective temperature of the companion is 13 400 ±1200 K from which we infer a luminosity of 3±1 L_☉. 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 on to 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- and B-type stars recently identified from their Kepler satellite light curves (KOI-74, KOI-81 and KIC 10657664). 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.

Based on observations made with ESO Telescopes at the La Silla Observatory under programme ID 084.D-0348(A).