A Search for Consistent Jet and Disk Rotation Signatures in RY Tau

TL;DR

This study investigates the rotation signatures of the RY Tau star system's disk and jet, finding clear disk rotation but no definitive jet rotation, thus providing insights into angular momentum transfer in young stellar objects.

Contribution

First to report a clear Keplerian rotation signature in RY Tau's disk and analyze jet velocity profiles to constrain jet launch regions.

Findings

Disk shows Keplerian rotation.

Jet velocity profiles vary near shocks and between shocks.

No definitive jet rotation detected, upper limit on jet toroidal velocity.

Abstract

We present a radial velocity study of the RY Tau jet-disk system, designed to determine whether a transfer of angular momentum from disk to jet can be observed. Many recent studies report on the rotation of T Tauri disks, and on what may be a signature of T Tauri jet rotation. However, due to observational difficulties, few studies report on both disk and jet within the same system to establish if the senses of rotation match and hence can be interpreted as a transfer of angular momentum. We report a clear signature of Keplerian rotation in the RY Tau disk, based on Plateau de Bure observations. We also report on the transverse radial velocity profile of the RY Tau jet close to the star. We identify two distinct profile shapes: a v-shape which appears near jet shock positions, and a flat profile which appears between shocks. We do not detect a rotation signature above 3 sigma uncertainty in any of our transverse cuts of the jet. Nevertheless, if the jet is currently in steady-state, the errors themselves provide a valuable upper limit on the jet toroidal velocity of 10 km/s, implying a launch radius of < 0.45 AU. However, possible contamination of jet kinematics, via shocks or precession, prevents any firm constraint on the jet launch point, since most of its angular momentum could be stored in magnetic form rather than in rotation of matter.