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arXiv 2007.05349astro-ph.SRastro-ph.HE
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一类新的充满洛希瓣的热亚矮星双星

A new class of Roche lobe-filling hot subdwarf binaries

Thomas Kupfer, Evan B. Bauer, Kevin B. Burdge, Jan van Roestel, Eric C. Bellm, Jim Fuller, JJ Hermes, Thomas R. Marsh, Lars Bildsten, Shrinivas R. Kulkarni, E. … 展开作者

Thomas Kupfer, Evan B. Bauer, Kevin B. Burdge, Jan van Roestel, Eric C. Bellm, Jim Fuller, JJ Hermes, Thomas R. Marsh, Lars Bildsten, Shrinivas R. Kulkarni, E. S. Phinney, Thomas A. Prince, Paula Szkody, Yuhan Yao, Andreas Irrgang, Ulrich Heber, David Schneider, Vik S. Dhillon, Gabriel Murawski, Andrew J. Drake, Dmitry A. Duev, Michael Feeney, Matthew J. Graham, Russ R. Laher, S. P. Littlefair, A. A. Mahabal, Frank J. Masci, Michael Porter, Dan Reiley, Hector Rodriguez, Ben Rusholme, David L. Shupe, Maayane T. Soumagnac

摘要:

我们目前的发现,第二个双星与罗氏叶填充热亚矮星转移质量的白矮星(WD)的同伴。这个56分钟的二进制文件是使用Zwicky Transient Facility的数据发现的。光谱观测揭示了一颗He-sdOB恒星,有效温度为$T_{\rm eff}=33,700\pm1000$ K,表面重力为$log(g)=5.54\pm0.11$。GTC+HiPERCAM的光变曲线主要由He-sdOB恒星的椭球形变形所控制,并显示了He-sdOB被吸积盘所食以及WD的弱食。我们推断出$M_{\rm sdOB}=0.41\pm0.04$ M $_\odot$的He-sdOB质量和$M_{\rm WD}=0.68\pm0.05$ M $_\odot$的WD质量。弱食意味着WD的黑体温度为$63,000\pm10,000$ K,半径为$R_{\rm WD}=0.0148\pm0.0020$ M $_\odot$,这与预期的WD如此高的温度相同。He-sdOB星可能正在经历氢壳燃烧,并将继续以$10^{-9} M_\odot {\rm yr}^{-1}$的速率为$\approx1$ Myrs转移质量,这与WD的高温度一致。热的亚矮星将变成WD,系统将在$\approx30$ Myrs合并。我们认为,银河系的红化可能会偏向于优先发现罗氏瓣填充系统在短暂的壳燃烧阶段的发现。使用红化校正的样品进行的研究应该揭示出在60-90分钟的双星中有大量的氦核燃烧的热亚矮星,它们具有$T_{\rm eff}\approx25,000$ K和WD。虽然还没有接触,但这些双星最终会通过引力波发射接触,并爆炸为亚发光热核超新星或演变为大质量的单个WD。

英文摘要:

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 $T_{\rm eff}=33,700\pm1000$ K and a surface gravity of $log(g)=5.54\pm0.11$. 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 $M_{\rm sdOB}=0.41\pm0.04$ M$_\odot$ and a WD mass of $M_{\rm WD}=0.68\pm0.05$ M$_\odot$. The weak eclipses imply a WD black-body temperature of $63,000\pm10,000$ K and a radius $R_{\rm WD}=0.0148\pm0.0020$ M$_\odot$ 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 $\approx1$ Myrs at a rate of $10^{-9} M_\odot {\rm yr}^{-1}$ which is consistent with the high WD temperature. The hot subdwarf will then turn into a WD and the system will merge in $\approx30$ Myrs. We suggest that Galactic reddening could bias discoveries towards 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 $T_{\rm eff}\approx25,000$ 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 sub-luminous thermonuclear supernova or evolve into a massive single WD.

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