标题： V471金牛座共同包层阶段的X射线证据 显示英文标题

标题： X-ray Evidence of the Common Envelope Phase of V471 Tauri

摘要： 利用钱德拉低能传输光栅光谱仪对前致密联星V471 Tau的观测，首次估算了K矮星组分的C/N丰度比。尽管白矮星组分主导着波长超过50埃的光谱，但在较短波长处观测到的X射线辐射完全来自K矮星的冕发射。碳和氮的H-like共振线给出了它们相对于太阳的对数丰度比[C/N]=-0.38±0.15，仅为目前公认太阳值的一半。我们将这一结果解释为该系统假定公共包层阶段的第一个明确的观测证据，在此期间K矮星表面被卷入红巨星包层的CN循环处理过的物质污染。我们利用测得的C/N比推断出在被吞没期间K矮星获得了0.015-0.04个太阳质量，这与最近K矮星光球中13C的初步探测以及红巨星伴星在公共包层阶段富含Li的情景下测量到的Li丰度一致。 显示英文摘要

摘要： Chandra Low Energy Transmission Grating Spectrograph observations of the pre-cataclysmic binary V471 Tau have been used to estimate the C/N abundance ratio of the K dwarf component for the first time. While the white dwarf component dominates the spectrum longward of 50 AA, at shorter wavelengths the observed X-ray emission is entirely due to coronal emission from the K dwarf. The H-like resonance lines of C and N yield an estimate of their logarithmic abundance ratio relative to the Sun of [C/N]=-0.38+/-0.15 - half of the currently accepted solar value. We interpret this result as the first clear observational evidence for the presumed common envelope phase of this system, during which the surface of the K dwarf was contaminated by CN-cycle processed material dredged up into the red giant envelope. We use the measured C/N ratio to deduce that 0.015-0.04 Msun was accreted by the K dwarf while engulfed, and show that this is consistent with a recent tentative detection of 13C in the K dwarf photosphere, and with the measured Li abundance in the scenario where the red giant companion was Li-rich during the common envelope phase.