English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Plus monthly

Global: Zendy Tools annual

Global: Zendy Tools monthly

Global: Zendy Free Plan

We present the discovery of EVR-CB-004, a close binary with a remnant stellarcore and an unseen white dwarf companion. The analysis in this work reveals theprimary is potentially an inflated hot subdwarf (sdO) and more likely is ararer post-blue horizontal branch (post-BHB) star. Post-BHBs are theshort-lived shell-burning final stage of a blue horizontal star or hot subdwarfbefore transitioning to a WD. This object was discovered using Evryscopephotometric data in a southern-all-sky hot subdwarf variability survey. Thephotometric light curve for EVR-CB-004 shows multi-component variability fromellipsoidal deformation of the primary and from Doppler boosting as well asgravitational limb darkening. EVR-CB-004 is one of just a handful of knownsystems, and has a long period (6.08426 hours) and large amplitude ellipsoidalmodulation (16.0 $\%$ change in brightness from maximum to minimum) for theseextremely close binary systems, while the properties of the primary make it atruly unique system. EVR-CB-004 also shows a peculiar low-amplitude (less than$1\%$) sinusoidal light curve variation with a period that is a 1/3 resonanceof the binary period. We tentatively identify this additional variation sourceas a tidally-induced resonant pulsation, and we suggest followup observationsthat could verify this interpretation. From the evolutionary state of thesystem, its components, and its mass fraction, EVR-CB-004 is a strong mergercandidate to form a single high-mass ($\approx1.2M_{\odot}$) WD. EVR-CB-004offers a glimpse into a brief phase of a remnant core evolution and secondaryvariation, not seen before in a compact binary.

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