%0 Journal Article
%T EL CVn-type binaries - Discovery of 17 helium white dwarf precursors in bright eclipsing binary star systems
%A P. F. L. Maxted
%A S. Bloemen
%A U. Heber
%A S. Geier
%A P. J. Wheatley
%A T. R. Marsh
%A E. Breedt
%A D. Sebastian
%A G. Faillace
%A C. Owen
%A D. Pulley
%A D. Smith
%A U. Kolb
%A C. A. Haswell
%A J. Southworth
%A D. R. Anderson
%A B. Smalley
%A A. Collier Cameron
%A L. Hebb
%A E. K. Simpson
%A R. G. West
%A J. Bochinski
%A R. Busuttil
%A S. Hadigal
%J Physics
%D 2013
%I arXiv
%R 10.1093/mnras/stt2007
%X The star 1SWASP J024743.37-251549.2 was recently discovered to be a binary star in which an A-type dwarf star eclipses the remnant of a disrupted red giant star (WASP0247-25B). The remnant is in a rarely-observed state evolving to higher effective temperatures at nearly constant luminosity prior to becoming a very low-mass white dwarf composed almost entirely of helium, i.e., it is a pre-He-WD. We have used the WASP photometric database to find 17 eclipsing binary stars with orbital periods P=0.7 to 2.2 days with similar lightcurves to 1SWASP J024743.37-251549.2. The only star in this group previously identified as a variable star is the brightest one, EL CVn, which we adopt as the prototype for this class of eclipsing binary star. The characteristic lightcurves of EL CVn-type stars show a total eclipse by an A-type dwarf star of a smaller, hotter star and a secondary eclipse of comparable depth to the primary eclipse. We have used new spectroscopic observations for 6 of these systems to confirm that the companions to the A-type stars in these binaries have very low masses (approximately 0.2 solar masses). This includes the companion to EL CVn which was not previously known to be a pre-He-WD. EL CVn-type binary star systems will enable us to study the formation of very low-mass white dwarfs in great detail, particularly in those cases where the pre-He-WD star shows non-radial pulsations similar to those recently discovered in WASP0247-25B.
%U http://arxiv.org/abs/1310.4863v1