Astrophys. J., 883, 51-51 (2019/September-3)
EVR-CB-001: an evolving, progenitor, white dwarf compact binary discovered with the Evryscope.
RATZLOFF J.K., BARLOW B.N., KUPFER T., CORCORAN K.A., GEIER S., BAUER E., CORBETT H.T., HOWARD W.S., GLAZIER A. and LAW N.M.
Abstract (from CDS):
We present EVR-CB-001, the discovery of a compact binary with an extremely low-mass (0.21 ± 0.05M☉) helium core white dwarf progenitor (pre-He WD) and an unseen low-mass (0.32 ± 0.06M☉) helium white dwarf (He WD) companion. He WDs are thought to evolve from the remnant helium-rich core of a main-sequence star stripped during the giant phase by a close companion. Low-mass He WDs are exotic objects (only about 0.2% of WDs are thought to be less than 0.3 M☉), and are expected to be found in compact binaries. Pre-He WDs are even rarer, and occupy the intermediate phase after the core is stripped, but before the star becomes a fully degenerate WD and with a larger radius (≃0.2R☉) than a typical WD. The primary component of EVR-CB-001 (the pre-He WD) was originally thought to be a hot subdwarf (sdB) star from its blue color and under-luminous magnitude, characteristic of sdBs. The mass, temperature (Teff = 18,500 ± 500 K), and surface gravity (log(g)=4.96±0.04) solutions from this work are lower than values for typical hot subdwarfs. The primary is likely to be a post-red-giant branch, pre-He WD contracting into a He WD, and at a stage that places it nearest to sdBs on color-magnitude and Teff-log(g) diagrams. EVR-CB-001 is expected to evolve into a fully double degenerate, compact system that should spin down and potentially evolve into a single hot subdwarf star. Single hot subdwarfs are observed, but progenitor systems have been elusive.
© 2019. The American Astronomical Society. All rights reserved.
Compact binary stars - White dwarf stars - B subdwarf stars - Stellar remnants - Compact objects
EVR -CB-NNN (No. 001).
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