INTERPRETING NEAR-INFRARED HYDROGEN LINE RATIOS IN T TAURI STARS
INTERPRETING NEAR-INFRARED HYDROGEN LINE RATIOS IN T TAURI STARS
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解释金牛座 T 星中的近红外氢谱线比率
DOI：
10.1088/0004-637x/778/2/148
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发表时间：
2013
期刊：
影响因子：
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通讯作者：
W. Feng
中科院分区：
文献类型：
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作者：
S. Edwards;J. Kwan;W. Fischer;L. Hillenbrand;Kimberly Finn;Kristina Fedorenko;W. Feng
在吸积年轻恒星的过程中，近红外的突出光谱特征之一是发射的帕邢和布拉克特系列。我们从 SpeX 光谱中检查 16 颗经典金牛座 T 星的氢谱线比率，并评估遮蔽和吸积的趋势。将观测到的线比率与线形成的两个理论模型进行比较：(1) Baker & Menzel 的辐射电离和复合案例 B，以及 (2) 一组旨在复制 T Tauri 风和磁吸积柱 (KF) 条件的局部线激励计算。虽然案例 B 与观测到的谱线比之间的比较表明金牛座 T 星的氢谱线形成区域中的电子密度和温度存在较大范围，但局部谱线激发模型的预测在多种诊断中给出了一致的结果。在局域线激发计算的假设下，我们发现氢线形成区的nH被限制在2×1010–2×1011 cm−3，其中吸积率较高的恒星的密度处于该范围的高端。由于消光的不确定性，温度没有被很好地描述，但落在碰撞激发产生线光子的预期范围内。我们引入了新的诊断方法，用于根据局部线激发计算中的近红外氢线比率来评估消光。
In accreting young stars, one of the prominent spectral features in the near-infrared is the Paschen and Brackett series in emission. We examine hydrogen line ratios for 16 classical T Tauri stars from SpeX spectra and assess the trends with veiling and accretion. The observed line ratios are compared with two theoretical models for line formation: (1) Baker & Menzel's Case B for radiative ionization and recombination and (2) a set of local line excitation calculations designed to replicate the conditions in T Tauri winds and magnetic accretion columns (KF). While the comparison between Case B and observed line ratios implies a wide range in electron density and temperature among the hydrogen line formation regions in T Tauri stars, the predictions of the local line excitation models give consistent results across multiple diagnostics. Under the assumptions of the local line excitation calculations, we find that nH in the hydrogen line formation region is constrained to 2 × 1010–2 × 1011 cm−3, where stars with higher accretion rates have densities at the higher end of this range. Because of uncertainties in extinction, temperature is not well delineated, but falls within the range expected for collisional excitation to produce the line photons. We introduce new diagnostics for assessing extinction based on near-infrared hydrogen line ratios from the local line excitation calculations.