The OmegaWhite Survey for Short-period Variable Stars. V. Discovery of an Ultracompact Hot Subdwarf Binary with a Compact Companion in a 44-minute Orbit
Kupfer T, Ramsay G, Van Roestel J, Brooks J, Macfarlane SA, Toma R, Groot PJ, Woudt PA, Bildsten L, Marsh TR, Green MJ, Breedt E, Kilkenny D, Freudenthal J, Geier S, Heber U, Bagnulo S, Blagorodnova N, Buckley DAH, Dhillon VS, Kulkarni SR, Lunnan R, Prince TA (2017)
Publication Status: Published
Publication Type: Journal article
Publication year: 2017
Journal
Publisher: IOP PUBLISHING LTD
Book Volume: 851
Article Number: ARTN 28
Journal Issue: 1
Abstract
We report the discovery of the ultracompact hot subdwarf (sdOB) binary OW J074106.0-294811.0 with an orbital period of P-orb = 44.66279 +/- 1.16 x 10(-4) minutes, making it the most compact hot subdwarf binary known. Spectroscopic observations using the VLT, Gemini and Keck telescopes revealed a He-sdOB primary with an intermediate helium abundance, T-eff = 39 400 +/- 500 K and log g = 5.74 +/- 0.09. High signal-to-noise ratio light curves show strong ellipsoidal modulation resulting in a derived sdOB mass M-sdOB= 0.23 +/- 0.12 M-circle dot with a WD companion (M-WD = 0.72 +/- 0.17 M-circle dot). The mass ratio was found to be q = M-sdOB/M-WD = 0.32 +/- 0.10. The derived mass for the He-sdOB is inconsistent with the canonical mass for hot subdwarfs of approximate to 0.47 M-circle dot. To put constraints on the structure and evolutionary history of the sdOB star we compared the derived T-eff, log g, and sdOB mass to evolutionary tracks of helium stars and helium white dwarfs calculated with Modules for Experiments in Stellar Astrophysics (MESA). We find that the best-fitting model is a helium white dwarf with a mass of 0.320 M-circle dot, which left the common envelope approximate to 1.1 Myr ago, which is consistent with the observations. As a helium white dwarf with a massive white dwarf companion, the object will reach contact in 17.6 Myr at an orbital period of 5 minutes. Depending on the spin-orbit synchronization timescale the object will either merge to form an R CrB star or end up as a stably accreting AM CVn-type system with a helium white dwarf donor.
Authors with CRIS profile
Involved external institutions
Eberhard Karls Universität Tübingen
Germany (DE)
California Institute of Technology (Caltech)
United States (USA) (US)
University of Sheffield
United Kingdom (GB)
Armagh Observatory
United Kingdom (GB)
University of the Western Cape (UWC)
South Africa (ZA)
Georg-August-Universität Göttingen
Germany (DE)
Radboud University Nijmegen
Netherlands (NL)
University of Warwick
United Kingdom (GB)
South African Astronomical Observatory (SAAO)
South Africa (ZA)
University of California
United States (USA) (US)
University of Cape Town (UCT)
South Africa (ZA)
Germany (DE)
California Institute of Technology (Caltech)
United States (USA) (US)
University of Sheffield
United Kingdom (GB)
Armagh Observatory
United Kingdom (GB)
University of the Western Cape (UWC)
South Africa (ZA)
Georg-August-Universität Göttingen
Germany (DE)
Radboud University Nijmegen
Netherlands (NL)
University of Warwick
United Kingdom (GB)
South African Astronomical Observatory (SAAO)
South Africa (ZA)
University of California
United States (USA) (US)
University of Cape Town (UCT)
South Africa (ZA)
How to cite
APA:
Kupfer, T., Ramsay, G., Van Roestel, J., Brooks, J., Macfarlane, S.A., Toma, R.,... Prince, T.A. (2017). The OmegaWhite Survey for Short-period Variable Stars. V. Discovery of an Ultracompact Hot Subdwarf Binary with a Compact Companion in a 44-minute Orbit. Astrophysical Journal, 851(1). https://doi.org/10.3847/1538-4357/aa9522
MLA:
Kupfer, Thomas, et al. "The OmegaWhite Survey for Short-period Variable Stars. V. Discovery of an Ultracompact Hot Subdwarf Binary with a Compact Companion in a 44-minute Orbit." Astrophysical Journal 851.1 (2017).
BibTeX: Download