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
Book Volume: 902
Journal Issue: 2
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.
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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