Jet rotation investigated in the near-ultraviolet with HST/STIS

TL;DR

This study used HST/STIS to investigate protostellar jet rotation in the near-ultraviolet, aiming to detect velocity differences indicative of rotation, but results were inconclusive due to system complexity and variability.

Contribution

First near-ultraviolet spectroscopic analysis of multiple T Tauri jets to search for rotation signatures, highlighting observational challenges and system variability.

Findings

Detected UV emission lines in five jets, but only RW Aur's jet had sufficient data for analysis.

Observed a velocity difference in RW Aur's approaching jet consistent with disk rotation, but not confirmed later.

Overall, no definitive evidence of jet rotation was found due to system complexity.

Abstract

We present results of the second phase of our near-ultraviolet investigation into protostellar jet rotation using HST/STIS. We obtain long-slit spectra at the base of five T Tauri jets to determine if there is a difference in radial velocity between the jet borders which may be interpreted as a rotation signature. These observations are extremely challenging and push the limits of current instrumentation, but have the potential to provide long-awaited observational support for the magneto-centrifugal mechanism of jet launching in which jets remove angular momentum from protostellar systems. We successfully detect all five jet targets (from RW Aur, HN Tau, DP Tau and CW Tau) in several near-ultraviolet emission lines, including the strong Mg II doublet. However, only RW Aur's bipolar jet presents sufficient signal-to-noise for analysis. The approaching jet lobe shows a difference of 10 km/s in a direction which agrees with the disk rotation sense, but is opposite to previously published optical measurements for the receding jet. The near-ultraviolet difference is not found six months later, nor is it found in the fainter receding jet. Overall, in the case of RW Aur, differences are not consistent with a simple jet rotation interpretation. Indeed, given the renowned complexity and variability of this system, it now seems likely that any rotation signature is confused by other influences, with the inevitable conclusion that RW Aur is not suited to a jet rotation study.