Density streams in the disc winds of Classical T Tauri stars

Spectral and photometric variability of the Classical T Tauri stars RY Tau and SU Aur from 2013 to 2022 is analysed. We find that in SU Aur the H alpha line's flux at radial velocity RV = -50 +/- 7 km s(-1) varies with a period P = 255 +/- 5 d. A similar effect previously discovered in RY Tau is confirmed with these new data: P = 21.6 d at RV = -95 +/- 5 km s. In both stars, the radial velocity of these variations, the period, and the mass of the star turn out to be related by Kepler's law, suggesting structural features on the disc plane orbiting at radii of 0.2 au in RY Tau and 0.9 au in SU Aur, respectively. Both stars have a large inclination of the accretion disc to the line of sight - so that the line of sight passes through the region of the disc wind. We propose there is an azimuthal asymmetry in the disc wind, presumably in the form of 'density streams,' caused by substructures of the accretion disc surface. These streams cannot dissipate until they go beyond the Alfven surface in the disc's magnetic field. These findings open up the possibility to learn about the structure of the inner accretion disc of CTTS on scales less than 1 au and to reveal the orbital distances related to the planet's formation.

Automated summary

In this study, the spectral and photometric variability of the Classical T Tauri stars RY Tau and SU Aur from 2013 to 2022 is analyzed. It is found that the flux of the H alpha line in SU Aur varies with a period of 255 +/- 5 d at a radial velocity of RV = -50 +/- 7 km s(-1). A similar effect is confirmed in RY Tau with a period of 21.6 d at RV = -95 +/- 5 km s. Kepler's law suggests that these variations in radial velocity, period, and star mass are related to structural features on the disc plane orbiting at radii of 0.2 au in RY Tau and 0.9 au in SU Aur. The findings provide an opportunity to understand the inner accretion disc structure of CTTS on scales less than 1 au and reveal orbital distances related to planet formation.