The First Ultracompact Roche Lobe–Filling Hot Subdwarf Binary
The First Ultracompact Roche Lobe–Filling Hot Subdwarf Binary
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DOI：
10.3847/1538-4357/ab72ff
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发表时间：
2020-02
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影响因子：
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通讯作者：
T. Kupfer;E. Bauer;T. Marsh;J. Roestel;E. Bellm;K. Burdge;M. Coughlin;J. Fuller;J. Hermes
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作者：
T. Kupfer;E. Bauer;T. Marsh;J. Roestel;E. Bellm;K. Burdge;M. Coughlin;J. Fuller;J. Hermes
我们报道了第一个短周期双星的发现，在这个双星中，一颗热的亚矮星(SdOB)填满了它的罗氏叶，并开始向它的同伴传递质量。该天体是在对银河系平面进行的一次专门的高节奏探测中发现的，名为兹维基瞬变设施，其周期为P=39.3401(1)分钟，使其成为目前已知的最紧凑的热次矮星双星。光谱观测与一颗中间的He-sdOB星相一致，其有效温度为42400±300K，表面引力为5.77±0.05。高信噪比的GTC+HiPERCAM光曲线主要由sdOB星的椭球形变和吸积盘对sdOB的蚀所主导。我们推测了一颗质量为0.337±0.015的低质量热亚矮星施主和一颗质量为0.545±0.020的白矮星吸引子。理论双星模型表明，热次矮星是在一个共同的包络阶段形成的，当时一颗2.5-2.8恒星在穿过赫茨斯普林格缺口时失去了包络。为了与它目前的、、和质量相匹配，我们估计后共同包络周期为≈150分钟，并发现这颗恒星目前正在经历氢壳燃烧。我们估计，这颗热亚矮星将成为一颗具有≈0.1厚氦层的白矮星，在≈17Myr之后与它的碳/氧白矮星合并，并可能以热核超新星的形式爆炸或形成一颗RCRB星。
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 = 42,400 ± 300 K and a surface gravity of = 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 and a white dwarf accretor with a mass MWD = 0.545 ± 0.020 . Theoretical binary modeling indicates the hot subdwarf formed during a common envelope phase when a 2.5–2.8 star lost its envelope when crossing the Hertzsprung gap. To match its current , , , and masses, we estimate a post–common envelope period of ≈ 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 , merge with its carbon/oxygen white dwarf companion after ≈17 Myr, and presumably explode as a thermonuclear supernova or form an R CrB star.