EL CVn-type binaries - Discovery of 17 helium white dwarf precursors in bright eclipsing binary star systems
Abstract
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.
Keywords
Cite
@article{arxiv.1310.4863,
title = {EL CVn-type binaries - Discovery of 17 helium white dwarf precursors in bright eclipsing binary star systems},
author = {P. F. L. Maxted and S. Bloemen and U. Heber and S. Geier and P. J. Wheatley and T. R. Marsh and E. Breedt and D. Sebastian and G. Faillace and C. Owen and D. Pulley and D. Smith and U. Kolb and C. A. Haswell and J. Southworth and D. R. Anderson and B. Smalley and A. Collier Cameron and L. Hebb and E. K. Simpson and R. G. West and J. Bochinski and R. Busuttil and S. Hadigal},
journal= {arXiv preprint arXiv:1310.4863},
year = {2015}
}
Comments
Accepted for publication in MNRAS. 18 pages