探测来自QS Vir的吸积X射线：是灾难性的还是大量的热空气？
Detection of accretion X-rays from QS Vir: cataclysmic or a lot of hot air?
摘要：
XMM-牛顿观测附近的“前激变”短周期（P_orb = 3.62 hr）双星QS Vir（EC 13471-1258），发现当白矮星从它的M2-4矮星伴星后面经过时，会出现有规律的窄X射线食。X射线辐射提供了白矮星上物质转移和吸积的清晰信号。低分辨率XMM-牛顿EPIC光谱与冷却流模型一致，表明吸积速率为Mdot= 1.7 \times 10^-13 M \odot /yr。在48 pc的距离，QS Vir是第二个最近的吸积激变变星，是迄今为止发现的非磁性系统中吸积率最低的变星之一。如果吸积效率为10%的量级，那么通过风来供给这种吸积需要风的质量损失率为Mdot ~ 2 \times 10^-12 M \odot /年。考虑到M矮星可能的质量损失率，这是不可能的高和纯风吸积不太可能。吸积盘特征的缺乏也给直接洛希瓣溢出带来了一些困难。我们推测，QS Vir是在洛希瓣溢出的边缘，所观察到的质量转移可以补充M矮星上的向上色球流，类似于太阳上的针状物和斑点，逃离洛希表面，随后被扫入白矮星洛希瓣。如果是这样的话，QS Vir将处于一个罕见的进化阶段，只持续了100万年。在主食期间估算的M矮星的X射线光度为L_X = 3 \times 10 ^28 erg/s，这与快速旋转的“饱和”K矮星和M矮星的X射线光度一致。
英文摘要：
An XMM-Newton observation of the nearby "pre-cataclysmic" short-period (P_orb = 3.62 hr) binary QS Vir (EC 13471-1258) revealed regular narrow X-ray eclipses when the white dwarf passed behind its M2-4 dwarf companion. The X-ray emission provides a clear signature of mass transfer and accretion onto the white dwarf. The low-resolution XMM-Newton EPIC spectra are consistent with a cooling flow model and indicate an accretion rate of Mdot= 1.7\times10^-13M\odot/yr. At 48 pc distant, QS Vir is then the second nearest accreting cataclysmic variable known, with one of the lowest accretion rates found to date for a non-magnetic system. To feed this accretion through a wind would require a wind mass loss rate of Mdot ~ 2 \times 10^-12M\odot/yr if the accretion efficiency is of the order of 10%. Consideration of likely mass loss rates for M dwarfs suggests this is improbably high and pure wind accretion unlikely. A lack of accretion disk signatures also presents some difficulties for direct Roche lobe overflow. We speculate that QS Vir is on the verge of Roche lobe overflow, and that the observed mass transfer could be supplemented by upward chromospheric flows on the M dwarf, analogous to spicules and mottles on the Sun, that escape the Roche surface to be subsequently swept up into the white dwarf Roche lobe. If so, QS Vir would be in a rare evolutionary phase lasting only a million years. The X-ray luminosity of the M dwarf estimated during primary eclipse is L_X = 3 \times 10^28 erg/s, which is consistent with that of rapidly rotating "saturated" K and M dwarfs.
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。
