中等质量前主序星的X射线辐射特征
Characterizing the X-ray Emission of Intermediate-Mass Pre-Main-Sequence Stars
摘要：
利用X射线和红外观测研究了船底座星云中三类年轻恒星的性质：中等质量（2- 5 ~M $_\odot$）的前主序星（IMPS;即中等质量的金牛T星），零龄主序星（AB）上的晚B星和A星，以及低质量的金牛T星（TTS）。我们将我们的源分为这三个子分类，并进一步确定盘轴承年轻恒星对象与无盘源，没有检测到红外（IR）过量发射使用IR（1- 8 $μ$ m）光谱能量分布建模。然后，我们进行X射线光谱拟合，以确定氢吸收柱密度（$N_{\rm H}$），吸收校正的X射线光度（$L_{\rm X}$），和日冕等离子体温度（$kT$）为每个源。我们发现IMPS和TTS的X射线能谱具有相似的$kT$和$N_{\rm H}$，平均$L_{\rm X}$ / $L_{\rm bol} \sim4\times10^{-4}$。IMPS在X射线方面比所有其他子分类系统都更明亮（$\sim$ 0.3 dex），中值$L_{\rm X} = 2.5\times10^{31}$ erg s $^{-1}$，而类似质量的AB星的X射线发射与TTS同伴一致。这些证据集中在IMPS X射线发射的磁日冕耀斑源上，这是TTS发射机制的放大版本。因此，IMPS提供了强大的探针的等时年龄的第一$\sim$ 10万年的大质量恒星人口的演变，因为他们的内在，日冕X射线发射迅速衰减后，他们开始沿着辐射轨道发展。我们建议，最明亮的（在X射线和IR）IMPS可以用来放置经验的限制的位置上的中等质量恒星出生线。
英文摘要：
We use X-ray and infrared observations to study the properties of three classes of young stars in the Carina Nebula: intermediate-mass (2--5~M$_\odot$) pre-main sequence stars (IMPS; i.e. intermediate-mass T Tauri stars), late-B and A stars on the zero-age main sequence (AB), and lower-mass T Tauri stars (TTS). We divide our sources among these three sub-classifications and further identify disk-bearing young stellar objects versus diskless sources with no detectable infrared (IR) excess emission using IR (1--8 $μ$m) spectral energy distribution modeling. We then perform X-ray spectral fitting to determine the hydrogen absorbing column density ($N_{\rm H}$), absorption-corrected X-ray luminosity ($L_{\rm X}$), and coronal plasma temperature ($kT$) for each source. We find that the X-ray spectra of both IMPS and TTS are characterized by similar $kT$ and $N_{\rm H}$, and on average $L_{\rm X}$/$L_{\rm bol} \sim4\times10^{-4}$. IMPS are systematically more luminous in X-rays (by $\sim$0.3 dex) than all other sub-classifications, with median $L_{\rm X} = 2.5\times10^{31}$ erg s$^{-1}$, while AB stars of similar masses have X-ray emission consistent with TTS companions. These lines of evidence converge on a magneto-coronal flaring source for IMPS X-ray emission, a scaled-up version of the TTS emission mechanism. IMPS therefore provide powerful probes of isochronal ages for the first $\sim$10 Myr in the evolution of a massive stellar population, because their intrinsic, coronal X-ray emission decays rapidly after they commence evolving along radiative tracks. We suggest that the most luminous (in both X-rays and IR) IMPS could be used to place empirical constraints on the location of the intermediate-mass stellar birth line.
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