Modulated accretion in the T Tauri star RY Tau – a stable MHD propeller or a planet at 0.2 au?
Modulated accretion in the T Tauri star RY Tau – a stable MHD propeller or a planet at 0.2 au?
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DOI：
10.1093/mnras/stab904
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发表时间：
2021-04
期刊：
影响因子：
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通讯作者：
P. Petrov;M. Romanova;K. Grankin;S. Artemenko;E. Babina;S. Gorda
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作者：
P. Petrov;M. Romanova;K. Grankin;S. Artemenko;E. Babina;S. Gorda
行星被认为是在恒星演化的早期阶段形成的，当时质量吸积仍在进行中。RY Tau是一颗金牛座T型恒星，年龄为几兆尔，吸积盘呈高倾角，因此视线既穿过了风，也穿过了吸积气流。在2013-2020年对该恒星进行的一系列长期光谱监测中，我们检测到在径向速度下（吸积）和流出（风）的Hα和Na i D吸收变化，周期约为22天。流入和流出气流的吸收率呈反相变化：流入增加，流出减少，反之亦然。这些“触发器”振荡在数年的观测中保持相位。我们认为这可能是由于磁碟-磁层边界的MHD过程在螺旋桨模式下造成的。另一种可能性是，一颗巨大的行星调节了圆盘中的某些过程，并提供了观察到的效果。如果是开普勒周期，则对应于0.2天文单位的距离，接近这颗恒星的尘埃升华半径。假设行星的存在可以通过径向速度测量来证实：如果行星质量≥2MJ，预期振幅≥90ms−1。
Planets are thought to form at the early stage of stellar evolution when the mass accretion is still ongoing. RY Tau is a T Tauri type star at the age of a few Myr, with accretion disc seen at high inclination, so that line of sight crosses both the wind and the accretion gas flows. In a long series of spectroscopic monitoring of the star in 2013-2020, we detected variations in Hα and Na i D absorptions at radial velocities of infall (accretion) and outflow (wind) with a period of about 22 days. The absorptions in the infalling and the outflowing gas streams vary in anti-phase: an increase of infall is accompanied by a decrease of outflow, and vice versa. These ‘flip-flop’ oscillations retain phase over several years of observations. We suggest that this may result from the MHD processes at the disk-magnetosphere boundary in the propeller mode. Another possibility is that a massive planet modulates some processes in the disc and provides the observed effects. The period, if Keplerian, corresponds to a distance of 0.2 AU, which is close to the dust sublimation radius in this star. The presence of the putative planet may be confirmed by radial velocity measurements: expected amplitude is ≥ 90 ms−1 if a planet mass is ≥ 2MJ .