Spectropolarimetry of the Classical T Tauri Star TW Hydrae
Spectropolarimetry of the Classical T Tauri Star TW Hydrae
复制标题
经典 T Tauri 星 TW Hydrae 的分光偏振法
DOI：
10.1086/509134
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发表时间：
2006
期刊：
影响因子：
--
通讯作者：
J. Valenti
中科院分区：
文献类型：
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作者：
Hao Yang;C. Johns–Krull;J. Valenti
本文介绍了经典金牛座T型星星长蛇座TW的高分辨率（R = 60，000）圆偏振光谱。我们分析了12条光球吸收线，并连续六个夜晚测量了净纵向磁场。虽然前五晚没有检测到净偏振，但在第六晚发现了一个显著的光球场Bz = 149 ± 33 G。为了排除虚假的仪器极化，我们将相同的分析技术应用于几个大地电磁线，检测没有显着的极化。我们进一步证明了这一领域的检测的现实表明，在这12个光球线的右和左偏振分量之间的分裂显示出线性趋势与Landé g因子倍波长平方，塞曼效应预测。然而，这种纵向场检测仍然远低于如果纯偶极磁几何结构导致先前报道的TW Hya的平均磁场强度为2.6 kG的情况。我们还在He I λ5876和Ca II λ8498发射线中检测到强圆偏振，表明在这些特征的线形成区域中存在强场。钙II线的偏振是大大弱于He I线，我们解释为由于一个更大的贡献，钙II线从色球发射中的偏振信号取消。然而，在钙II线极化的存在表明，吸积冲击经典金牛座T星不产生狭窄的钙的红外三线发射功能。
We present high-resolution (R ≈ 60,000) circular spectropolarimetry of the classical T Tauri star TW Hydrae. We analyze 12 photospheric absorption lines and measure the net longitudinal magnetic field for six consecutive nights. While no net polarization is detected the first five nights, a significant photospheric field of Bz = 149 ± 33 G is found on the sixth night. To rule out spurious instrumental polarization, we apply the same analysis technique to several nonmagnetic telluric lines, detecting no significant polarization. We further demonstrate the reality of this field detection by showing that the splitting between right and left polarized components in these 12 photospheric lines shows a linear trend with Landé g-factor times wavelength squared, as predicted by the Zeeman effect. However, this longitudinal field detection is still much lower than that which would result if a pure dipole magnetic geometry is responsible for the mean magnetic field strength of 2.6 kG previously reported for TW Hya. We also detect strong circular polarization in the He I λ5876 and Ca II λ8498 emission lines, indicating a strong field in the line formation region of these features. The polarization of the Ca II line is substantially weaker than that of the He I line, which we interpret as being due to a larger contribution to the Ca II line from chromospheric emission in which the polarization signals cancel. However, the presence of polarization in the Ca II line indicates that accretion shocks on classical T Tauri stars do produce narrow emission features in the infrared triplet lines of calcium.