Density streams in the disc winds of Classical T Tauri stars

TL;DR

This study analyzes spectral variability in Classical T Tauri stars RY Tau and SU Aur, revealing periodic density streams in their disc winds that relate to inner disc structures and potential planet formation zones.

Contribution

It provides new evidence of azimuthal asymmetries in disc winds caused by substructures in the accretion discs of CTTS, linking spectral variability to disc features within 1 AU.

Findings

Periodic spectral variations linked to disc structures.

Evidence of azimuthal asymmetries in disc winds.

Disc features correspond to orbital radii of 0.2 and 0.9 AU.

Abstract

Spectral and photometric variability of the Classical T Tauri stars RY Tau and SU Aur from 2013 to 2022 is analyzed. We find that in SU Aur the H-alpha line's flux at radial velocity RV = -50 +- 7 km/s varies with a period P = 255 +- 5 days. A similar effect previously discovered in RY Tau is confirmed with these new data: P = 21.6 days 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.