Magnetospheric accretion on the fully convective classical T Tauri star DN Tau
Magnetospheric accretion on the fully convective classical T Tauri star DN Tau
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DOI：
10.1093/mnras/stt1622
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发表时间：
2013-08
影响因子：
4.8
通讯作者：
J. Donati;S. Gregory;S. Alencar;G. Hussain;J. Bouvier;M. Jardine;F. Ménard;C. Dougados;
中科院分区：
文献类型：
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作者：
J. Donati;S. Gregory;S. Alencar;G. Hussain;J. Bouvier;M. Jardine;F. Ménard;C. Dougados;
我们在此报告在“磁原恒星和行星”计划中，使用加拿大-法国-夏威夷望远镜的 ESPaDOnS 对经典金牛座 T 星 DN Tau 进行的分光偏振观测（两个历元）的结果。我们推测DN Tau光球温度为3,950±50 K，光度为0.8±0.2 L⊙，自转周期为6.32 d，是一颗≃2 Myr年龄的全对流0.65 ± 0.05 M⊙恒星，半径为1.9 ± 0.2 R⊙，在35 ± 10°倾角下观察。 。在光球和吸积动力发射线中均检测到清晰的圆偏振塞曼特征，探测高达 1.8 kG 的纵向场（在 He i D3 吸积代理中）。在光球和吸积线中检测到的塞曼特征的旋转调制在我们的两次运行之间是不同的，这进一步证明 cTTS 场是由非静止发电机产生的。使用断层扫描成像，我们重建了两个时期 DN Tau 表面的大尺度场图、光球亮度图和吸积动力发射图。我们发现磁拓扑主要是极向的，并且很大程度上是轴对称的，八极分量（极性强度 0.6–0.8 kG）比偶极分量（极性强度 ≃0.3–0.5 kG）大 1.5–2.0 倍。 DN Tau 在两个时期都以向极地吸积为主。然而，DN Tau 的大尺度偶极子成分太弱，无法破坏周围吸积盘超过共转半径的 65-90%（在此圆盘开普勒周期与恒星自转周期相匹配），这表明 DN Tau 尽管处于完全对流状态，但已经开始旋转。
We report here results of spectropolarimetric observations of the classical T Tauri star DN Tau carried out (at 2 epochs) with ESPaDOnS at the Canada-France-Hawaii Telescope within the ‘Magnetic Protostars and Planets’ programme. We infer that DN Tau, with a photospheric temperature of 3,950±50 K, a luminosity of 0.8±0.2 L⊙ and a rotation period of 6.32 d, is a ≃2 Myr-old fully-convective 0.65 ± 0.05 M⊙ star with a radius of 1.9 ± 0.2 R⊙, viewed at an inclination of 35 ± 10 ◦ . Clear circularly-polarized Zeeman signatures are detected in both photospheric and accretion-powered emission lines, probing longitudinal fields of up to 1.8 kG (in the He i D3 accretion proxy). Rotational modulation of Zeeman signatures, detected both in photospheric and accretion lines, is different between our 2 runs, providing further evidence that fields of cTTSs are generated by non-stationary dynamos. Using tomographic imaging, we reconstruct maps of the large-scale field, of the photospheric brightness and of the accretion-powered emission at the surface of DN Tau at both epochs. We find that the magnetic topology is mostly poloidal, and largely axisymmetric, with an octupolar component (of polar strength 0.6–0.8 kG) 1.5–2.0× larger than the dipolar component (of polar strength ≃0.3–0.5 kG). DN Tau features dominantly poleward accretion at both epochs. The large-scale dipole component of DN Tau is however too weak to disrupt the surrounding accretion disc further than 65–90% of the corotation radius (at which the disc Keplerian period matches the stellar rotation period), suggesting that DN Tau is already spinning up despite being fully convective.