Molecular Mapping of DR Tau's Protoplanetary Disk, Envelope, Outflow, and Large-Scale Spiral Arm

TL;DR

This study uses NOEMA millimeter interferometry to map DR Tau's protoplanetary disk, revealing complex structures including an envelope, outflow, and a large spiral arm, highlighting the importance of molecular imaging in understanding young stellar objects.

Contribution

First detailed molecular imaging of DR Tau's environment, revealing large-scale structures and complex kinematics beyond the disk, advancing understanding of its variability and disk instabilities.

Findings

Detection of a large spiral arm extending 1200 au

Identification of an envelope and asymmetric outflow

Molecular emissions originate mainly from the disk

Abstract

DR Tau has been noted for its unusually high variability in comparison with other T Tauri stars. Although it is one of the most extensively studied pre-main sequence stars, observations with millimeter interferometry have so far been relatively limited. We present NOEMA images of $^{12}$CO, $^{13}$CO, C$^{18}$O, SO, DCO$^+$, and H$_2$CO toward DR Tau at a resolution of $\sim0.5''$ ($\sim100$ au). In addition to the protoplanetary disk, CO emission reveals an envelope, a faint asymmetric outflow, and a spiral arm with a clump. The $\sim1200$ au extent of the CO arm far exceeds that of the spiral arms previously detected in scattered light, which underlines the necessity of sensitive molecular imaging for contextualizing the disk environment. The kinematics and compact emission distribution of C$^{18}$O, SO, DCO$^+$, and H$_2$CO indicate that they originate primarily from within the Keplerian circumstellar disk. The SO emission, though, also exhibits an asymmetry that may be due to interaction with infalling material or unresolved substructure. The complex environment of DR Tau is reminiscent of those of outbursting FUor sources and some EXor sources, suggesting that DR Tau's extreme stellar activity could likewise be linked to disk instabilities promoted by large-scale infall.