Physical Conditions of Accreting Gas in T Tauri Star Systems
Physical Conditions of Accreting Gas in T Tauri Star Systems
复制标题
金牛座 T 星系统中吸积气体的物理条件
DOI：
10.1086/591487
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发表时间：
2008
期刊：
影响因子：
--
通讯作者：
M. Nelson
中科院分区：
文献类型：
--
作者：
J. Bary;S. Matt;M. Skrutskie;John C. Wilson;D. Peterson;M. Nelson
我们展示了对金牛座-御夫座恒星形成区域中活跃吸积的金牛座 T 星 (TTS) 进行的低分辨率 (R≃ 300) 近红外光谱变异性调查的结果。在 15 个经典 T Tauri 系统的 73 个光谱中检测到 Paschen 和 Brackett 系列 H I 重组谱线。所有观测值的 Panup/Paβ、Brnup/Brγ 和 Brγ/Panup H I 线比的值在加权平均值上表现出 ≲20% 的离散度，不仅在源与源之间，而且在同一源的历元间变化也是如此。为 Paschen 和 Brackett 系列中的每个比率以及 Brγ/Panup 线比率确定了代表性或“全局”值。将观察到的线比值与案例 B 氢复合线理论的温度和电子密度相关模型预测的线比值进行了比较。测量的线比在统计上非常适合严格限制的温度范围（T≲ 2000 K）和电子密度（109 cm -3 < ne≲ 1010 cm−3）。将观察到的线比值与光学厚和薄局部热力学平衡情况预测的值进行比较，排除了发射 H I 气体的这些条件。因此，发射与非 LTE 重组气体的起源一致。虽然电子密度范围与现有磁层吸积模型预测的气体密度一致，但情况 B 比较所限制的温度范围远低于吸积气体的预期温度范围。较冷的气体温度将需要非热激发过程（例如，日冕/吸积相关的 X 射线和紫外光子）来为观测到的线发射提供动力。
We present results from a low-resolution (R≃ 300) near-infrared spectroscopic variability survey of actively accreting T Tauri stars (TTSs) in the Taurus-Auriga star-forming region. Paschen and Brackett series H I recombination lines were detected in 73 spectra of 15 classical T Tauri systems. The values of the Panup/Paβ, Brnup/Brγ, and Brγ/Panup H I line ratios for all observations exhibit a scatter of ≲20% about the weighted mean, not only from source to source, but also for epoch-to-epoch variations in the same source. A representative or “global” value was determined for each ratio in both the Paschen and Brackett series, as well as the Brγ/Panup line ratios. A comparison of observed line ratio values was made to those predicted by the temperature- and electron density-dependent models of case B hydrogen recombination line theory. The measured line ratios are statistically well fit by a tightly constrained range of temperatures (T≲ 2000 K) and electron densities (109 cm −3 < ne≲ 1010 cm−3). A comparison of the observed line ratio values to the values predicted by the optically thick and thin local thermodynamic equilibrium cases rules out these conditions for the emitting H I gas. Therefore, the emission is consistent with having an origin in a non-LTE recombining gas. While the range of electron densities is consistent with the gas densities predicted by existing magnetospheric accretion models, the temperature range constrained by the case B comparison is considerably lower than that expected for accreting gas. The cooler gas temperatures will require a nonthermal excitation process (e.g., coronal/accretion-related X-rays and UV photons) to power the observed line emission.