Dynamical structure of the inner 100 AU of the deeply embedded protostar IRAS 16293-2422

TL;DR

This study uses high-resolution submillimeter observations to analyze the gas kinematics around the protostar IRAS 16293-2422, revealing a rotating structure that suggests the presence of a pseudo-disk rather than simple Keplerian rotation.

Contribution

The paper provides detailed high-resolution imaging of the inner 100 AU of IRAS 16293-2422, demonstrating complex rotation influenced by the envelope mass, and proposes the candidate of a pseudo-disk.

Findings

Velocity gradient indicates rotation on 50-400 AU scales.

Rotation cannot be explained by simple Keplerian dynamics.

Evidence suggests a pseudo-disk structure.

Abstract

A fundamental question about the early evolution of low-mass protostars is when circumstellar disks may form. High angular resolution observations of molecular transitions in the (sub)millimeter wavelength windows make it possible to investigate the kinematics of the gas around newly-formed stars, for example to identify the presence of rotation and infall. IRAS 16293-2422 was observed with the extended Submillimeter Array (eSMA) resulting in subarcsecond resolution (0.46" x 0.29", i.e. $\sim$ 55 $\times$ 35~AU) images of compact emission from the C$^{17}$O (3-2) and C$^{34}$S (7-6) transitions at 337~GHz (0.89~mm). To recover the more extended emission we have combined the eSMA data with SMA observations of the same molecules. The emission of C$^{17}$O (3-2) and C$^{34}$S (7-6) both show a velocity gradient oriented along a northeast-southwest direction with respect to the continuum marking the location of one of the components of the binary, IRAS16293A. Our combined eSMA and SMA observations show that the velocity field on the 50--400~AU scales is consistent with a rotating structure. It cannot be explained by simple Keplerian rotation around a single point mass but rather needs to take into account the enclosed envelope mass at the radii where the observed lines are excited. We suggest that IRAS 16293-2422 could be among the best candidates to observe a pseudo-disk with future high angular resolution observations.