[论文解读] High-resolution TNG spectra of T Tauri stars: Near-IR GIANO observations of the young variables XZ Tau and DR Tau

S. Antoniucci, B. Nisini+7 more|arXiv (Cornell University)|Jun 16, 2017

Astrophysics and Star Formation Studies参考文献 51被引用 7

一句话总结

本研究利用位于意大利特克斯科皮奥·纳索纳莱伽利望远镜上的GIANO仪器，采用高分辨率近红外光谱（R ~ 50,000）研究了两颗EXor型T Tauri星XZ Tau和DR Tau的吸积与喷流活动。结果表明，XZ Tau表现出强烈且可变的高速喷流，以及与近期吸积爆发相关的金属线；而DR Tau则显示出稳定的喷流和与无尘气态盘一致的较高温度包覆，凸显了宽波段近红外光谱在分离年轻恒星系统中磁层、吸积与喷流成分方面的强大能力。

ABSTRACT

We used the TNG/GIANO instrument to obtain near-IR high-resolution spectra (R~50000) of XZ Tau and DR Tau, two actively accreting T Tauri stars classified as EXors. The analysis of the observed features provides information on the properties of the inner disk, the accretion columns, and the winds. Both sources display composite HI line profiles, with contributions from both accreting gas and high-velocity winds. These lines become more symmetric and narrower with increasing upper energy, which may be interpreted in terms of two components with different decrements or imputed to self-absorption effects. XZ Tau shows a relatively high state of activity with respect to literature observations. The variation of the HeI 1.08um line blue-shifted absorption suggests that the inner wind has undergone a dramatic change in its velocity structure, connected with a recent accretion event. DR Tau has a more stable wind as its HeI 1.08um absorption is stable in time in spite of strong variability of the emission component. The IR veiling can be interpreted as due to blackbody emission at temperatures of 1600K for XZ Tau and 2300K DR Tau, with emitting areas ~30 times larger than the star. For XZ Tau these conditions are consistent with emission from the inner rim of the dusty disk, while for DR Tau the fairly high temperature may suggest an origin from a thick gaseous disk within the dust sublimation radius. Strong and broad metallic lines, mainly from CI and FeI, are detected in XZ Tau, similar to those observed in other EXor sources during burst phases. DR Tau shows weaker and narrower metallic lines, despite its larger accretion luminosity. This suggests that accretion is not the only driver of metallic line excitation. Our observations show the potential of wide-band, high-resolution near-IR spectroscopy to simultaneously probe the phenomena that occur in the star-disk interaction region.

研究动机与目标

• 利用高分辨率近红外光谱表征变星T Tauri星的星-盘相互作用区域。
• 分离观测光谱特征中来自吸积柱、喷流和内盘发射的贡献。
• 研究两颗活跃吸积的EXor型T Tauri星XZ Tau和DR Tau的内盘和喷流气体的物理条件与变异性。
• 确定红外包覆的起源及其对内盘温度和结构的启示。

提出的方法

• 利用位于Telescopio Nazionale Galileo望远镜上的GIANO仪器获取高分辨率近红外光谱（R ~ 50,000）。
• 分析H i Paschen和Brackett线、He i 1.08 μm线以及金属线（Fe i、C i等）的轮廓形状和等效宽度。
• 通过将目标光谱与相同光谱型的光球模板比较来测量包覆，并使用黑体模型拟合以推断温度和辐射区域。
• 利用允许线中发射与吸收成分的运动学结构，识别吸积流与高速喷流的贡献。
• 分析H2 2.12 μm线轮廓，以区分盘束缚发射与激波激发成分。
• 同时覆盖近红外波段的宽波段范围，实现了对多个诊断指标中包覆和线轮廓的一致比较。

实验结果

研究问题

• RQ1 高分辨率近红外光谱揭示的XZ Tau和DR Tau的内盘及吸积区域的运动学与物理条件是什么？
• RQ2 H i和He i线中发射与吸收特征的变异性如何与吸积和喷流活动的变化相关联？
• RQ3 这些系统中红外包覆的起源是什么？它揭示了内盘的温度和结构的哪些信息？
• RQ4 为何XZ Tau和DR Tau尽管DR Tau的吸积光度更高，但表现出不同的金属线激发水平？
• RQ5 高分辨率近红外光谱在多大程度上能够分辨同一光谱范围内吸积、喷流和盘发射的贡献？

主要发现

• XZ Tau表现出高度可变的高速喷流，其He i 1.08 μm线的蓝移吸收深度发生剧烈变化，表明近期发生了吸积事件。
• 尽管发射线表现出强烈变异性，DR Tau仍显示出稳定的喷流成分，表明吸积与喷流动力学在不同空间区域可能呈现脱耦。
• XZ Tau的红外包覆与1600 K黑体辐射一致，辐射区域约为恒星表面面积的30倍，可能来自内尘埃盘边缘。
• DR Tau的包覆需要更高的温度（2300 K），表明其来自尘埃亚稳化半径内的无尘、光学厚气态盘。
• XZ Tau中强而宽的金属线（Fe i、C i）与爆发期活动相关，而DR Tau中较弱且较窄的线表明仅靠吸积无法解释金属线的激发。
• XZ Tau的H2 2.12 μm线显示出一个窄的盘成分和一个宽的蓝移成分，可能是在广角喷流中由激波激发，进一步证实了复杂的喷流动力学。