A New Class of Roche Lobe–filling Hot Subdwarf Binaries
A New Class of Roche Lobe–filling Hot Subdwarf Binaries
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DOI：
10.3847/2041-8213/aba3c2
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发表时间：
2020-07
期刊：
影响因子：
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通讯作者：
T. Kupfer;E. Bauer;K. Burdge;J. Roestel;E. Bellm;J. Fuller;J. Hermes;T. Marsh;L. Bildsten-
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作者：
T. Kupfer;E. Bauer;K. Burdge;J. Roestel;E. Bellm;J. Fuller;J. Hermes;T. Marsh;L. Bildsten-
我们发现了第二颗双星，其中一颗充满罗氏叶的热亚矮星将质量转移给了一颗白矮星(WD)。这个56分钟的双星是使用兹维基瞬变设备的数据发现的。光谱观测显示，这是一颗He-sdOB星，有效温度为33,700±1000 K，表面重力为log(G)=5.54±0.11。GTC+HipERCAM光曲线以He-sdOB星的椭球形变为主，既有吸积盘对He-sdOB的食，也有WD的弱食。推算出He-SdOB质量为MsdOB=0.41±0.04M⊙，WD质量为MWD=0.68±0.05M⊙。弱食意味着WD黑体温度为63,000±10,000 K，半径RWD=0.0148±0.0020 R⊙，与预期的WD如此高的温度一样。He-SdOB恒星可能正在经历氢壳层燃烧，并将继续以10−9M⊙yr−1的速度传递质量，这与WD的高温度是一致的。热亚矮星随后将变成WD，该系统将在≈30Myr合并。我们认为，银河系变红可能会使发现偏向于在短暂的贝壳燃烧阶段优先发现罗氏肺叶填充系统。使用红化校正样本的研究应该揭示出一大群氦核心燃烧的热亚矮星，它们的TEF≈为25,000 K，WDS的双星时间为60-90分钟。虽然还没有接触，但这些双星最终会通过引力波发射而接触，并以亚发光热核超新星的形式爆炸，或者演化成大质量的单个WD。
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 of Teff = 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 of MsdOB = 0.41 ± 0.04 M⊙ and a WD mass of MWD = 0.68 ± 0.05 M⊙. The weak eclipses imply a WD blackbody temperature of 63,000 ± 10,000 K and a radius RWD = 0.0148 ± 0.0020 R⊙ as 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 M⊙ yr−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 with Teff ≈ 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.