A seven-Earth-radius helium-burning star inside a 20.5-min detached binary

Fuente: arXiv

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Bibliographic Details
Main Authors:	Lin, Jie, Wu, Chengyuan, Xiong, Heran, Wang, Xiaofeng, Nemeth, Peter, Han, Zhanwen, Li, Jiangdan, Elias-Rosa, Nancy, Salmaso, Irene, Filippenko, Alexei V., Brink, Thomas G., Yang, Yi, Chen, Xuefei, Yan, Shengyu, Zhang, Jujia, Guo, Sufen, Cai, Yongzhi, Mo, Jun, Xi, Gaobo, Liu, Jialian, Guo, Jincheng, Xia, Qiqi, Xiang, Danfeng, Li, Gaici, Li, Zhenwei, Zheng, WeiKang, Zhang, Jicheng, Liu, Qichun, Guo, Fangzhou, Chen, Liyang, Li, Wenxiong
Format:	Preprint
Published:	2023
Subjects:	Solar and Stellar Astrophysics Earth and Planetary Astrophysics High Energy Astrophysical Phenomena Instrumentation and Methods for Astrophysics
Online Access:	Acceder al recurso
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_version_	1866916120835915776
author	Lin, Jie Wu, Chengyuan Xiong, Heran Wang, Xiaofeng Nemeth, Peter Han, Zhanwen Li, Jiangdan Elias-Rosa, Nancy Salmaso, Irene Filippenko, Alexei V. Brink, Thomas G. Yang, Yi Chen, Xuefei Yan, Shengyu Zhang, Jujia Guo, Sufen Cai, Yongzhi Mo, Jun Xi, Gaobo Liu, Jialian Guo, Jincheng Xia, Qiqi Xiang, Danfeng Li, Gaici Li, Zhenwei Zheng, WeiKang Zhang, Jicheng Liu, Qichun Guo, Fangzhou Chen, Liyang Li, Wenxiong
author_facet	Lin, Jie Wu, Chengyuan Xiong, Heran Wang, Xiaofeng Nemeth, Peter Han, Zhanwen Li, Jiangdan Elias-Rosa, Nancy Salmaso, Irene Filippenko, Alexei V. Brink, Thomas G. Yang, Yi Chen, Xuefei Yan, Shengyu Zhang, Jujia Guo, Sufen Cai, Yongzhi Mo, Jun Xi, Gaobo Liu, Jialian Guo, Jincheng Xia, Qiqi Xiang, Danfeng Li, Gaici Li, Zhenwei Zheng, WeiKang Zhang, Jicheng Liu, Qichun Guo, Fangzhou Chen, Liyang Li, Wenxiong
contents	Binary evolution theory predicts that the second common envelope (CE) ejection can produce low-mass (0.32-0.36 Msun) subdwarf B (sdB) stars inside ultrashort-orbital-period binary systems, as their helium cores are ignited under nondegenerate conditions. With the orbital decay driven by gravitational-wave (GW) radiation, the minimum orbital periods of detached sdB binaries could be as short as ~20 minutes. However, only four sdB binaries with orbital periods below an hour have been reported so far, while none of them has an orbital period approaching the above theoretical limit. Here we report the discovery of a 20.5-minute-orbital-period ellipsoidal binary, TMTS J052610.43+593445.1, in which the visible star is being tidally deformed by an invisible carbon-oxygen white dwarf (WD) companion. The visible component is inferred to be an sdB star with a mass of ~0.33 Msun, approaching that of helium-ignition limit, although a He-core WD cannot be completely ruled out. In particular, the radius of this low-mass sdB star is only 0.066 Rsun, about seven Earth radii, possibly representing the most compact nondegenerate star ever known. Such a system provides a key clue to map the binary evolution scheme from the second CE ejection to the formation of AM CVn stars having a helium-star donor, and it will also serve as a crucial verification binary of space-borne GW detectors in the future.
format	Preprint
id	arxiv_https___arxiv_org_abs_2312_13612
institution	arXiv
publishDate	2023
record_format	arxiv
spellingShingle	A seven-Earth-radius helium-burning star inside a 20.5-min detached binary Lin, Jie Wu, Chengyuan Xiong, Heran Wang, Xiaofeng Nemeth, Peter Han, Zhanwen Li, Jiangdan Elias-Rosa, Nancy Salmaso, Irene Filippenko, Alexei V. Brink, Thomas G. Yang, Yi Chen, Xuefei Yan, Shengyu Zhang, Jujia Guo, Sufen Cai, Yongzhi Mo, Jun Xi, Gaobo Liu, Jialian Guo, Jincheng Xia, Qiqi Xiang, Danfeng Li, Gaici Li, Zhenwei Zheng, WeiKang Zhang, Jicheng Liu, Qichun Guo, Fangzhou Chen, Liyang Li, Wenxiong Solar and Stellar Astrophysics Earth and Planetary Astrophysics High Energy Astrophysical Phenomena Instrumentation and Methods for Astrophysics Binary evolution theory predicts that the second common envelope (CE) ejection can produce low-mass (0.32-0.36 Msun) subdwarf B (sdB) stars inside ultrashort-orbital-period binary systems, as their helium cores are ignited under nondegenerate conditions. With the orbital decay driven by gravitational-wave (GW) radiation, the minimum orbital periods of detached sdB binaries could be as short as ~20 minutes. However, only four sdB binaries with orbital periods below an hour have been reported so far, while none of them has an orbital period approaching the above theoretical limit. Here we report the discovery of a 20.5-minute-orbital-period ellipsoidal binary, TMTS J052610.43+593445.1, in which the visible star is being tidally deformed by an invisible carbon-oxygen white dwarf (WD) companion. The visible component is inferred to be an sdB star with a mass of ~0.33 Msun, approaching that of helium-ignition limit, although a He-core WD cannot be completely ruled out. In particular, the radius of this low-mass sdB star is only 0.066 Rsun, about seven Earth radii, possibly representing the most compact nondegenerate star ever known. Such a system provides a key clue to map the binary evolution scheme from the second CE ejection to the formation of AM CVn stars having a helium-star donor, and it will also serve as a crucial verification binary of space-borne GW detectors in the future.
title	A seven-Earth-radius helium-burning star inside a 20.5-min detached binary
topic	Solar and Stellar Astrophysics Earth and Planetary Astrophysics High Energy Astrophysical Phenomena Instrumentation and Methods for Astrophysics
url	https://arxiv.org/abs/2312.13612