2020/02/04 by Thomas Kupfer, Evan B. Bauer, Thomas R. Marsh +29 · 70 citations
Physics and Astronomy · #Accretion (finance) #Astrophysical Phenomena and Observations #Astrophysics and Star Formation Studies #Binary number #Binary star #Common envelope #Light curve #Roche lobe #Stellar, planetary, and galactic studies #Subdwarf #Surface gravity #White dwarf #astro-ph.SR
paper · pdf · open access · doi:10.3847/1538-4357/ab72ff
published in The Astrophysical Journal 891(1), 45 (IOP Publishing) · accepted for publication in ApJ, 21 pages, 12 figures and 4 tables
arxiv created 2020/02/04 · openalex publication_date 2020/03/01 · arxiv updated 2020/03/11 · openalex created_date 2020/03/13 · openalex updated_date 2026/08/05
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 P\rm orb=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 T\rm eff=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 M\rm sdOB=0.337±0.015 M_\odot and a white dwarf accretor with a mass M\rm WD=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\rm orb, T\rm eff, log(g), and masses, we estimate a post-common envelope period of P\rm orb≈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_\odot 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.