A New Class of Roche Lobe-filling Hot Subdwarf Binaries

Kupfer T, Bauer E, Burdge K, van Roestel J, Bellm E, Fuller J, Hermes J, Marsh TR, Bildsten L, Kulkarni SR, Phinney ES, Prince TA, Szkody P, Yao Y, Heber U, Schneider D, Dhillon VS, Murawski G, Drake AJ, Duev DA, Feeney M, Graham MJ, Laher RR, Littlefair SP, Mahabal AA, Masci FJ, Porter M, Reiley D, Rodriguez H, Rusholme B, Shupe DL, Soumagnac MT, Irrgang A (2020)

Publication Status: Published

Publication Type: Journal article

Publication year: 2020

Journal

Astrophysical Journal Letters American Astronomical Society

Publisher: IOP PUBLISHING LTD

Book Volume: 898

Article Number: ARTN L25

Journal Issue: 1

DOI: 10.3847/2041-8213/aba3c2

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 ofT(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 ofM(sdOB) = 0.41 0.04Mand a WD mass ofM(WD) = 0.68 0.05M. The weak eclipses imply a WD blackbody temperature of 63,000 10,000 K and a radiusR(WD) = 0.0148 0.0020Ras 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)Myr(-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 withT(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.

Authors with CRIS profile

Ulrich Heber Professur für Astronomie und Astrophysik David Schneider Professur für Astronomie und Astrophysik Andreas Irrgang Dr.Karl-Remeis-Sternwarte Bamberg, Astronomisches Institut

Involved external institutions

University of Washington US United States (USA) (US) California Institute of Technology (Caltech) US United States (USA) (US) University of California US United States (USA) (US) Instituto de Astrofísica de Canarias (IAC) ES Spain (ES) University of Warwick GB United Kingdom (GB) Lawrence Berkeley National Laboratory (LBNL) US United States (USA) (US) Boston University US United States (USA) (US) University of Sheffield GB United Kingdom (GB)

How to cite

APA:

Kupfer, T., Bauer, E., Burdge, K., van Roestel, J., Bellm, E., Fuller, J.,... Irrgang, A. (2020). A New Class of Roche Lobe-filling Hot Subdwarf Binaries. Astrophysical Journal Letters, 898(1). https://doi.org/10.3847/2041-8213/aba3c2

MLA:

Kupfer, Thomas, et al. "A New Class of Roche Lobe-filling Hot Subdwarf Binaries." Astrophysical Journal Letters 898.1 (2020).

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