EL CVn-type binaries - discovery of 17 helium white dwarf precursors in bright eclipsing binary star systems
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Date
11/01/2014Author
Grant ID
ST/J001651/1
PP/F000065/1
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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.
Citation
Maxted , P F L , Bloemen , S , Heber , U , Geier , S , Wheatley , P J , Marsh , T R , Breedt , E , Sebastian , D , Faillace , G , Owen , C , Pulley , D , Smith , D , Kolb , U , Haswell , C A , Southworth , J , Anderson , D R , Smalley , B , Cameron , A C , Hebb , L , Simpson , E K , West , R G , Bochinski , J , Busuttil , R & Hadigal , S 2014 , ' EL CVn-type binaries - discovery of 17 helium white dwarf precursors in bright eclipsing binary star systems ' , Monthly Notices of the Royal Astronomical Society , vol. 437 , no. 2 , pp. 1681-1697 . https://doi.org/10.1093/mnras/stt2007
Publication
Monthly Notices of the Royal Astronomical Society
Status
Peer reviewed
ISSN
0035-8711Type
Journal article
Description
This work was supported by funding from the European Research Council under the European Community’s Seventh Framework Programme (FP7/2007–2013)/ERC grant agreement no 227224 (PROSPERITY), as well as from the Science and Technology Facilities Council (grant numbers ST/I001719/1, ST/J001384/1)Collections
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