EL CVn-type binaries - discovery of 17 helium white dwarf precursors in bright eclipsing binary star systems

P. F. L. Maxted*, S. Bloemen, U. Heber, S. Geier, P. J. Wheatley, T. R. Marsh, E. Breedt, D. Sebastian, G. Faillace, C. Owen, D. Pulley, D. Smith, U. Kolb, C. A. Haswell, J. Southworth, D. R. Anderson, B. Smalley, A. Collier Cameron, L. Hebb, E. K. SimpsonR. G. West, J. Bochinski, R. Busuttil, S. Hadigal

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

60 Citations (Scopus)


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 (WASP 0247-25 B). 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-helium white dwarf (pre-He-WD). We have used the photometric database from the Wide Angle Search for Planets (WASP) to find 17 eclipsing binary stars with orbital periods P = 0.7-2.2 d with similar light curves 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 light curves 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 six of these systems to confirm that the companions to the A-type stars in these binaries have very low masses (≈0.2MΘ). 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 WASP0247-25 B.

Original languageEnglish
Pages (from-to)1681-1697
Number of pages17
JournalMonthly Notices of the Royal Astronomical Society
Issue number2
Early online date20 Nov 2013
Publication statusPublished - 11 Jan 2014


  • Binaries: close
  • Binaries: eclipsing
  • Binaries: spectroscopic
  • Stars: individual: 1SWASP J024743.37-251549.2
  • Stars: individual: EL CVn
  • Sky survey 2MASS
  • Low-mass
  • Stellar spectra
  • Main-sequence
  • Light-curves
  • Evolution
  • Library
  • Kepler
  • Core
  • Calibration


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