EVR-CB-004: An Inflated Hot Subdwarf O Star plus Unseen WD Companion in a Compact Binary Discovered with the Evryscope

Ratzloff JK, Kupfer T, Barlow BN, Schneider D, Marsh TR, Heber U, Corcoran KA, Bauer E, Hämmerich S, Corbett HT, Glazier A, Howard WS, Law NM (2020)

Publication Type: Journal article

Publication year: 2020

Journal

Astrophysical Journal American Astronomical Society

Book Volume: 902

Journal Issue: 2

DOI: 10.3847/1538-4357/abb5b2

Abstract

We present the discovery of EVR-CB-004, a close binary with a remnant stellar core and an unseen white dwarf (WD) companion. The analysis in this work reveals that the primary is potentially an inflated hot subdwarf (sdO) and more likely is a rarer post-blue horizontal branch (post-BHB) star. Post-BHBs are the short-lived shell-burning final stage of a blue horizontal star or hot subdwarf before transitioning to a WD. This object was discovered using Evryscope photometric data in a southern all-sky hot subdwarf variability survey. The photometric light curve for EVR-CB-004 shows multicomponent variability from ellipsoidal deformation of the primary and Doppler boosting, as well as gravitational limb darkening. The binary EVR-CB-004 is one of just a handful of known systems and has a long period (6.08426 hr) and large-amplitude ellipsoidal modulation (16.0% change in brightness from maximum to minimum) for these extremely close binary systems, while the properties of the primary make it a truly unique system. It also shows a peculiar low-amplitude (less than 1%) sinusoidal light-curve variation with a period that is a 1/3 resonance of the binary period. We tentatively identify this additional variation source as a tidally induced resonant pulsation, and we suggest follow-up observations that could verify this interpretation. From the evolutionary state of the system, its components, and its mass fraction, EVR-CB-004 is a strong merger candidate to form a single high-mass (1.2M) WD. It offers a glimpse into a brief phase of remnant core evolution and secondary variation not seen before in a compact binary.

Authors with CRIS profile

David Schneider Dr.Karl-Remeis-Sternwarte Bamberg, Astronomisches Institut Ulrich Heber Naturwissenschaftliche Fakultät Steven Hämmerich Dr.Karl-Remeis-Sternwarte Bamberg, Astronomisches Institut

Involved external institutions

University of North Carolina at Chapel Hill US United States (USA) (US) University of California US United States (USA) (US) High Point University US United States (USA) (US) University of Warwick GB United Kingdom (GB)

How to cite

APA:

Ratzloff, J.K., Kupfer, T., Barlow, B.N., Schneider, D., Marsh, T.R., Heber, U.,... Law, N.M. (2020). EVR-CB-004: An Inflated Hot Subdwarf O Star plus Unseen WD Companion in a Compact Binary Discovered with the Evryscope. Astrophysical Journal, 902(2). https://doi.org/10.3847/1538-4357/abb5b2

MLA:

Ratzloff, Jeffrey K., et al. "EVR-CB-004: An Inflated Hot Subdwarf O Star plus Unseen WD Companion in a Compact Binary Discovered with the Evryscope." Astrophysical Journal 902.2 (2020).

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