The Winds from HL Tau

TL;DR

This study uses high-resolution ALMA data to analyze the bipolar molecular outflow from HL Tau, revealing magnetic collimation effects and quantifying outflow velocities in the context of star formation.

Contribution

It provides detailed characterization of the high-velocity molecular outflow from HL Tau, linking outflow morphology to magnetic collimation and star formation processes.

Findings

Bipolar outflow with opening angle narrowing from 90° to 60°

Outflow velocity approximately 2.4 km/s after inclination correction

Evidence of magnetic collimation shaping the outflow

Abstract

Outflowing motions, whether a wind launched from the disk, a jet launched from the protostar, or the entrained molecular outflow, appear to be an ubiquitous feature of star formation. These outwards motions have a number of root causes, and how they manifest is intricately linked to their environment as well as the process of star formation itself. Using the ALMA Science Verification data of HL Tau, we investigate the high velocity molecular gas being removed from the system as a result of the star formation process. We aim to place these motions in context with the optically detected jet, and the disk. With these high resolution ($\sim 1"$) ALMA observations of CO (J=1-0), we quantify the outwards motions of the molecular gas. We find evidence for a bipolar outwards flow, with an opening angle, as measured in the red-shifted lobe, starting off at 90$^\circ$, and narrowing to 60$^\circ$ further from the disk, likely because of magnetic collimation. Its outwards velocity, corrected for inclination angle is of order 2.4 km s$^{-1}$.