Kupfer, T., Bauer, E.B., Marsh, T.R. et al. (29 more authors) (2020) The first ultracompact Roche lobe-filling hot subdwarf binary. The Astrophysical Journal, 891 (1). 45. ISSN 0004-637X
Abstract
We report the discovery of the first short period binary in which a hot subdwarf star (sdOB) fills its Roche lobe and started mass transfer to its companion. The object was discovered as part of a dedicated high-cadence survey of the Galactic Plane named the Zwicky Transient Facility and exhibits a period of Porb=39.3401(1) min, making it the most compact hot subdwarf binary currently known. Spectroscopic observations are consistent with an intermediate He-sdOB star with an effective temperature of Teff=42,400±300 K and a surface gravity of log(g)=5.77±0.05. A high-signal-to noise GTC+HiPERCAM light curve is dominated by the ellipsoidal deformation of the sdOB star and an eclipse of the sdOB by an accretion disk. We infer a low-mass hot subdwarf donor with a mass MsdOB=0.337±0.015 M⊙ and a white dwarf accretor with a mass MWD=0.545±0.020 M⊙. Theoretical binary modeling indicates the hot subdwarf formed during a common envelope phase when a 2.5−2.8 M⊙ star lost its envelope when crossing the Hertzsprung Gap. To match its current Porb, Teff, log(g), and masses, we estimate a post-common envelope period of Porb≈150 min, and find the sdOB star is currently undergoing hydrogen shell burning. We estimate that the hot subdwarf will become a white dwarf with a thick helium layer of ≈0.1 M⊙ and will merge with its carbon/oxygen white dwarf companion after ≈17 Myr and presumably explode as a thermonuclear supernova or form an R CrB star.
Metadata
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Copyright, Publisher and Additional Information: | © 2020 American Astronomical Society. This is an author-produced version of a paper subsequently published in Astrophysical Journal. Uploaded in accordance with the publisher's self-archiving policy. | ||||
Keywords: | B subdwarf stars; Stellar evolution; Compact binary stars; White dwarf stars | ||||
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Institution: | The University of Sheffield | ||||
Academic Units: | The University of Sheffield > Faculty of Science (Sheffield) > Department of Physics and Astronomy (Sheffield) | ||||
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Depositing User: | Symplectic Sheffield | ||||
Date Deposited: | 19 Feb 2020 12:20 | ||||
Last Modified: | 06 May 2020 16:30 | ||||
Status: | Published | ||||
Publisher: | American Astronomical Society | ||||
Refereed: | Yes | ||||
Identification Number: | https://doi.org/10.3847/1538-4357/ab72ff | ||||
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