Kupfer, T., Bauer, E.B., Burdge, K.B. et al. (30 more authors) (2020) A new class of Roche lobe–filling hot subdwarf binaries. Astrophysical Journal Letters, 898 (1). L25. ISSN 2041-8205
Abstract
We present the discovery of the second binary with a Roche lobe–filling hot subdwarf transferring mass to a white dwarf (WD) companion. This 56 minute binary was discovered using data from the Zwicky Transient Facility. Spectroscopic observations reveal an He-sdOB star with an effective temperature of T eff = 33,700 ± 1000 K and a surface gravity of log(g) = 5.54 ± 0.11. The GTC+HiPERCAM light curve is dominated by the ellipsoidal deformation of the He-sdOB star and shows an eclipse of the He-sdOB by an accretion disk as well as a weak eclipse of the WD. We infer a He-sdOB mass of M sdOB = 0.41 ± 0.04 M ⊙ and a WD mass of M WD = 0.68 ± 0.05 M ⊙. The weak eclipses imply a WD blackbody temperature of 63,000 ± 10,000 K and a radius R WD = 0.0148 ± 0.0020 R ⊙ as expected for a WD of such high temperature. The He-sdOB star is likely undergoing hydrogen shell burning and will continue transferring mass for ≈1 Myr at a rate of 10−9 M ⊙ yr−1, which is consistent with the high WD temperature. The hot subdwarf will then turn into a WD and the system will merge in ≈30 Myr. We suggest that Galactic reddening could bias discoveries toward preferentially finding Roche lobe–filling systems during the short-lived shell-burning phase. Studies using reddening-corrected samples should reveal a large population of helium core–burning hot subdwarfs with T eff ≈ 25,000 K in binaries of 60–90 minutes with WDs. Though not yet in contact, these binaries would eventually come into contact through gravitational-wave emission and explode as a subluminous thermonuclear supernova or evolve into a massive single WD.
Metadata
Item Type: | Article |
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Authors/Creators: |
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Copyright, Publisher and Additional Information: | © 2020. The American Astronomical Society. This is an author-produced version of a paper subsequently published in Astrophysical Journal Letters. Uploaded in accordance with the publisher's self-archiving policy. |
Keywords: | B subdwarf stars; Stellar evolution; White dwarf stars; Compact binary stars; Stellar accretion |
Dates: |
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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) |
Depositing User: | Symplectic Sheffield |
Date Deposited: | 19 Nov 2020 14:15 |
Last Modified: | 23 Jul 2021 00:38 |
Status: | Published |
Publisher: | American Astronomical Society |
Refereed: | Yes |
Identification Number: | 10.3847/2041-8213/aba3c2 |
Related URLs: | |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:165618 |