Journal Article

Discovery of a stripped red giant core in a bright eclipsing binary system*

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 and R. G. West

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 418, issue 2, pages 1156-1164
Published in print December 2011 | ISSN: 0035-8711
Published online November 2011 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2011.19567.x
Discovery of a stripped red giant core in a bright eclipsing binary system*

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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 IC-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.

Keywords: binaries: close; binaries: eclipsing; binaries: spectroscopic; stars: individual: 1SWASP J024743.37−251549.2; stars: peculiar

Journal Article.  6025 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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