Origins of the H, He i and Ca ii line emission in classical T Tauri stars
Origins of the H, He i and Ca ii line emission in classical T Tauri stars
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DOI：
10.1111/j.1365-2966.2010.17863.x
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发表时间：
2010-10
影响因子：
4.8
通讯作者：
J. Kwan;W. Fischer
中科院分区：
文献类型：
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作者：
J. Kwan;W. Fischer
我们进行本地激发计算，以获得线的不透明度和发射率比，并将它们与观察到的H，He I，O I，Ca II和Na I线的性质进行比较，以确定密度，温度和光子电离率的必要条件。我们发现，紫外光电离是最有可能的激发机制，产生的He Iλ10830不透明，产生所有相关的吸收功能。我们还计算了在观测速度为vobs =± 150 km s-1时径向风和下落模型的比线通量。所有的模型结果，连同观察到的吸收和发射特性之间的相关性和窄和宽的发射组件之间，被用来推断的起源强H，He I和Ca II宽线发射。我们的结论是，前两个主要出现在一个径向流出，是高度cloudly。大部分风的体积被密度为10.9 cm −3的气体填充，光学厚度为He Iλ10830和Hα，但光学厚度为He Iλ5876、Paγ和Ca II红外三重态。光学厚的He Iλ5876发射主要发生在密度≥ 1011 cm-3和温度≥1.5 × 104 K的区域，而光学厚的Hα和Paγ发射主要发生在密度约1011 cm-3和温度在8750 ~ 1.25 × 104 K之间的区域。在产生观测到的线通量在一个给定的vobs，这些发射团的覆盖因子是足够小的，不会引起显着的吸收恒星和面纱连续的He I或H线。强烈的钙II宽线发射可能出现在磁层吸积流和磁盘边界层的气体消散之前，沿沿着磁场线下落的旋转能量的一部分。所需的密度和温度分别为≤ 1012 cm −3和≤7500 K。
We perform local excitation calculations to obtain line opacities and emissivity ratios, and compare them with observed properties of H, He I ,O I ,C aII and Na I lines to determine the requisite conditions of density, temperature and photon ionization rate. We find that ultraviolet photoionization is the most probable excitation mechanism for generating the He Iλ10830 opacities that produce all the associated absorption features. We also calculate the specific line flux at an observed velocity of vobs =± 150 km s −1 for both radial wind and infall models. All the model results, together with observed correlations between absorption and emission features and between narrow and broad emission components, are used to deduce the origins of the strong H, He I and Ca II broad line emission. We conclude that the first two arise primarily in a radial outflow that is highly clumpy. The bulk of the wind volume is filled by gas at a density ∼10 9 cm −3 and optically thick to He Iλ10830 and Hα, but optically thin to He Iλ5876, Paγ and the Ca II infrared triplet. The optically thick He Iλ5876 emission occurs mostly in regions of density ≥10 11 cm −3 and temperature ≥1.5 × 10 4 K, while the optically thick Hα and Paγ emission occurs mostly in regions of density around 10 11 cm −3 and temperature between 8750 and 1.25 × 10 4 K. In producing the observed line fluxes at a given vobs, the covering factor of these emission clumps is sufficiently small to not incur significant absorption of the stellar and veiling continua in either He I or H lines. The strong Ca II broad line emission likely arises in both the magnetospheric accretion flow and the disc boundary layer where the gases dissipate part of their rotational energies before infalling along magnetic field lines. The needed density and temperature are ∼10 12 cm −3 and ≤7500 K, respectively.