标题： 钱德拉对M 31核球球状星团恒星X射线发射率的研究 显示英文标题

标题： A Chandra Study of The Stellar X-ray Emissivity of Globular Clusters in M\,31 Bulge

摘要： X射线发射率（即单位恒星质量的光度）是球状星团动力学演化历史的重要指标。 基于深度档案中的\textit{钱德拉}观测数据，我们报告了44个球状星团（GCs）在M 31核球中的0.5-8 keV光度$L_{\rm X} \lesssim 10^{35} {\rm~erg~s^{-1}}$的堆叠分析，这些星团被认为主要由灾难性变星（CVs）和日冕活动双星（ABs）主导。 我们在0.5-8 keV波段在$5\sigma$级别上获得了显著检测。 每个GC的平均X射线光度和平均X射线发射率分别确定为$5.3 \pm 1.6\times10^{33}\rm~erg~s^{-1}$和$13.2\pm4.3\times10^{27}\rm~erg~{\rm s^{-1}~M^{-1}_{\odot}}$。 这两个值都与银河系球状星团（MW GCs）的值一致。 此外，M31球状星团的测量发射率也与银河系场星一致。 大质量球状星团的X射线光度略高于小质量的星团。 大质量球状星团的发射率（$4.5\pm 2.4\times10^{27}{\rm~erg~s^{-1}~M^{-1}_{\odot}}$）也低于小质量星团（$15.0\pm 7.8\times10^{27}{\rm~erg~s^{-1}~M^{-1}_{\odot}}$），这与CVs和ABs的前身在大质量球状星团中通过恒星相遇更有效地被破坏的情景一致。 未发现X射线发射率与球状星团颜色或球状星团投影银河中心距离之间的依赖关系。 显示英文摘要

摘要： The X-ray emissivity (i.e., luminosity per unit stellar mass) of globular clusters are an important indicator of their dynamical evolution history. Based on deep archival \textit{Chandra} observations, we report a stacking analysis of 44 globular clusters (GCs) with 0.5-8 keV luminosities $L_{\rm X} \lesssim 10^{35} {\rm~erg~s^{-1}}$ in the M\,31 bulge, which are supposed to be dominated by cataclysmic variables (CVs) and coronally active binaries (ABs). We obtain a significant detection at $5\sigma$ level in 0.5-8 keV band. The average X-ray luminosity per GC and the average X-ray emissivity are determined to be $5.3 \pm 1.6\times10^{33}\rm~erg~s^{-1}$ and $13.2\pm4.3\times10^{27}\rm~erg~{\rm s^{-1}~M^{-1}_{\odot}}$, respectively. Both of these values are consistent with those of MW GCs. What's more, the measured emissivity of M31 GCs is also consistent with that of the MW field stars. Massive GCs have X-ray luminosities which are marginally higher with less massive ones. Massive GCs also show a lower emissivity ($4.5\pm 2.4\times10^{27}{\rm~erg~s^{-1}~M^{-1}_{\odot}}$) than less massive ones ($15.0\pm 7.8\times10^{27}{\rm~erg~s^{-1}~M^{-1}_{\odot}}$), which is consistent with the scenario that the (progenitors of) CVs and ABs were more efficiently destructed via stellar encounters in the more massive GCs. No dependence of the X-ray emissivity on GC color or on the projected galactocentric distance of GCs were found.