arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 1808.03423astro-ph.SR
收藏

激变前变星的最小轨道周期

Minimum Orbital Period of Pre-Cataclysmic Variables

L. Nelson, J. Schwab, M. Ristic, S. Rappaport

摘要:

目前已经发现了20多个前激变变星(pre-CV)系统,它们的轨道周期从250分钟到68分钟不等。前激变变星由一颗白矮星或热亚矮星主星和一颗低质量伴星组成,伴星已经成功地喷射出主星的共同包层,但从伴星到主星的质量转移尚未开始。在这个短周期范围内,相当一部分伴星可能是质量为$\lesssim 0.07 \, M_\odot$的褐矮星,或者是MS底部的恒星($\lesssim 0.1 M_\odot$)。这些短周期前CV的发现提出了一个问题--这类系统最短的可能轨道周期是多少?我们运行了500个棕矮星/低质量主序模型,其中包括质量范围从0.002到0.1 $M_\odot$的{ \tt MESA}。我们发现最短可能的轨道周期是40分钟,相应的褐矮星质量为0.07 $M_\odot$的年龄等于哈勃时间。我们讨论了这些系统过去的演变,通过共同的信封,并建议,许多系统与目前的白矮星的主要可能已经退出了共同的信封与主要作为一个氦燃烧热亚矮星。我们还描述了所观察到的系统,其中包括一个阶段的CV低于传统的周期最小值的未来演变。

英文摘要:

More than 20 pre-cataclysmic variable (pre-CV) systems have now been discovered with very short orbital periods ranging from 250 min down to 68 min. A pre-CV consists of a white dwarf or hot subdwarf primary and a low-mass companion star, where the companion star has successfully ejected the common envelope of the primary progenitor, but mass transfer from the companion star to the primary has not yet commenced. In this short-period range, a substantial fraction of the companion stars are likely to be either brown dwarfs with masses $\lesssim 0.07 \, M_\odot$ or stars at the bottom of the MS ($\lesssim 0.1 M_\odot$). The discovery of these short-period pre-CVs raises the question -- what is the shortest possible orbital period of such systems? We ran 500 brown dwarf/low-mass main sequence models with {\tt MESA} that cover the mass range from 0.002 to 0.1 $M_\odot$. We find the shortest possible orbital period is 40 min with a corresponding brown dwarf mass of 0.07 $M_\odot$ for an age equal to a Hubble time. We discuss the past evolution of these systems through the common envelope and suggest that many of the systems with present day white dwarf primaries may have exited the common envelope with the primary as a helium burning hot subdwarf. We also characterize the future evolution of the observed systems, which includes a phase as CVs below the conventional period minimum.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

↑