Modulated accretion in T Tauri star RY Tau -- stable MHD propeller or a planet at 0.2 AU?

TL;DR

This study observes periodic accretion and wind variations in T Tauri star RY Tau, suggesting they may be caused by either MHD processes at the disk-magnetosphere boundary or a close-in planet at 0.2 AU, with potential planetary detection via radial velocities.

Contribution

It proposes a novel interpretation of accretion-wind variability in RY Tau as due to either MHD propeller effects or a planet at 0.2 AU, supported by long-term spectroscopic data.

Findings

Detected 22-day periodic variations in accretion and wind signatures.

Anti-phase behavior of infall and outflow streams observed over years.

Potential planetary companion with >90 m/s radial velocity amplitude.

Abstract

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 H-alpha and NaI 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 m/s if a planet mass is > 2 Mj.