Characterizing the X-ray Emission of Intermediate-Mass Pre-Main-Sequence Stars

Probabilistic H-R Diagrams (pHRD) and X-ray spectral results for sources in the IMPS Paper (abstract below).

phrds.zip (uncompressed size ~ 30 MB): Contains flip through PS (postscript) of the pHRDs for each source. The PS are separated by disk status (disky/diskless) and IR classification (AB, IMPS, TTS, and Unc). MIR names are used.

XRay_spectra_and_lightcurves.zip (uncompressed size ~50 MB): Contains PS of binned best X-ray spectral fit (binned for display purposes), sequenced light curve, and stacked light curve for each source. X-ray names are used.

spectra.ps: A compilation of the binned X-ray spectral fits for our entire sample as a flip through PS

Paper Abstract: We use X-ray and infrared observations to study the properties of three classes of young stars in the Carina Nebula:  intermediate-mass \edit1{(2--5~M$_\odot$)} pre-main sequence stars (IMPS\edit1{; 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 $\mu$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.

本数据集包含IMPS论文（摘要见下文）中天体的概率赫罗图（Probabilistic H-R Diagrams，pHRD）与X射线光谱分析结果。

phrds.zip（解压后大小约30 MB）：包含各天体pHRD的可翻阅后置脚本（PostScript，PS）文件。该压缩包内的PS文件按天体的盘状态（有盘/无盘）与红外分类（AB、IMPS、TTS及未分类）进行分组，文件采用中红外（Mid-Infrared，MIR）命名规则。

XRay_spectra_and_lightcurves.zip（解压后大小约50 MB）：包含各天体的分箱最佳X射线光谱拟合结果（为便于展示已做分箱处理）、时序光变曲线以及堆叠光变曲线的PS文件。文件采用X射线命名规则。

spectra.ps：本文件为全样本天体的分箱X射线光谱拟合结果汇编，以可翻阅PS文件形式呈现。

论文摘要：本研究利用X射线与红外观测数据，对船底座星云中的三类年轻恒星开展特性研究：中等质量（2~5倍太阳质量）主序前星（IMPS，即中等质量金牛T星）、零龄主序晚期B型与A型星（AB型），以及低质量金牛T星（TTS）。我们将研究天体划分为上述三个子类，并通过红外（1~8 μm）光谱能量分布建模，进一步区分出拥有吸积盘的年轻恒星天体与无红外超额辐射的无盘天体。随后我们开展X射线光谱拟合，以确定每个天体的氢吸收柱密度（$N_{
m H}$）、吸收校正后的X射线光度（$L_{
m X}$）以及日冕等离子体温度（$kT$）。
研究发现，IMPS与TTS的X射线光谱具有相近的$kT$与$N_{
m H}$值，平均$L_{
m X}/L_{
m bol}$约为$4 imes10^{-4}$。IMPS的X射线光度系统性高于其他所有子类（高出约0.3 dex），其中位数$L_{
m X}$为$2.5 imes10^{31}$ erg s$^{-1}$；而同等质量的AB型星的X射线辐射特性与TTS伴星一致。上述多项证据共同表明，IMPS的X射线辐射源于磁冕耀斑过程，其机制是TTS辐射机制的尺度放大版本。因此，IMPS可作为首个约10 Myr内大质量恒星族群演化的等时年龄探针，因为当它们开始沿辐射演化轨道演化后，其本征日冕X射线辐射会快速衰减。我们提出，兼具高X射线与红外光度的IMPS可用于为中等质量恒星诞生线的位置提供经验约束。