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The first ultracompact Roche lobe-filling hot subdwarf binary
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(2020) The first ultracompact Roche lobe-filling hot subdwarf binary. The Astrophysical Journal, 891 (1). 45. doi:10.3847/1538-4357/ab72ff
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Official URL: https://doi.org/10.3847/1538-4357/ab72ff
Abstract
We report the discovery of the first short-period binary in which a hot subdwarf star (sdOB) filled 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 P = 39.3401(1) minutes, 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 ${T}_{\mathrm{eff}}$ = 42,400 ± 300 K and a surface gravity of $\mathrm{log}(g)$ = 5.77 ± 0.05. A high signal-to-noise ratio 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 ${M}_{\odot }$ and a white dwarf accretor with a mass MWD = 0.545 ± 0.020 ${M}_{\odot }$. Theoretical binary modeling indicates the hot subdwarf formed during a common envelope phase when a 2.5–2.8 ${M}_{\odot }$ star lost its envelope when crossing the Hertzsprung gap. To match its current ${P}_{\mathrm{orb}}$, ${T}_{\mathrm{eff}}$, $\mathrm{log}(g)$, and masses, we estimate a post–common envelope period of ${P}_{\mathrm{orb}}$ ≈ 150 minutes and find that 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 ${M}_{\odot }$, merge with its carbon/oxygen white dwarf companion after ≈17 Myr, and presumably explode as a thermonuclear supernova or form an R CrB star.
| Item Type: | Journal Article | ||||||||||||
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| Subjects: | Q Science > QB Astronomy | ||||||||||||
| Divisions: | Faculty of Science, Engineering and Medicine > Science > Physics | ||||||||||||
| Library of Congress Subject Headings (LCSH): | Double stars, Double stars -- Spectra, White dwarf stars | ||||||||||||
| Journal or Publication Title: | The Astrophysical Journal | ||||||||||||
| Publisher: | Institute of Physics Publishing, Inc. | ||||||||||||
| ISSN: | 0004-637X | ||||||||||||
| Official Date: | 3 March 2020 | ||||||||||||
| Dates: |
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| Volume: | 891 | ||||||||||||
| Number: | 1 | ||||||||||||
| Article Number: | 45 | ||||||||||||
| DOI: | 10.3847/1538-4357/ab72ff | ||||||||||||
| Status: | Peer Reviewed | ||||||||||||
| Publication Status: | Published | ||||||||||||
| Reuse Statement (publisher, data, author rights): | © 2020. The American Astronomical Society. | ||||||||||||
| Access rights to Published version: | Restricted or Subscription Access | ||||||||||||
| RIOXX Funder/Project Grant: |
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