Modulated accretion in the T Tauri star RY Tau – a stable MHD propeller or a planet at 0.2 au?
Monthly Notices of the Royal Astronomical Society(2021)
摘要
Planets are thought to form at the early stage of stellar evolution when mass accretion is still ongoing. RY Tau is a T Tauri type star at the age of a few Myr, with an accretion disc seen at high inclination, so that the line of sight crosses both the wind and accretion gas flows. In a long series of spectroscopic monitoring of the star over the period 2013–2020, we detected variations in H
$\, {\alpha }$
and Na i D absorptions at radial velocities of infall (accretion) and outflow (wind) with a period of about 22 d. The absorptions in the infalling and outflowing gas streams vary in antiphase: 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 magnetohydrodynamics processes at the disc–magnetosphere boundary in the propeller mode. Another possibility is that a massive planet is modulating some processes in the disc and is providing 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 can be confirmed by radial velocity measurements: the expected amplitude is ≥90 m s
−1
if the planet mass is ≥2 M
J
.
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关键词
line: profiles,stars: individual: RY Tau,stars: variables: T Tauri, Herbig Ae/Be,stars: winds, outflows
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