Velocity-resolved hot water emission detected toward HL Tau with the Submillimeter Array

TL;DR

This study detects velocity-resolved hot water emission from HL Tau, revealing it originates from the protostellar jet or wind, and demonstrates the potential of SMA for studying water in protostellar systems.

Contribution

First detection of velocity-resolved hot water emission from HL Tau showing its origin in jet or wind, highlighting SMA's capability for future water studies in protostars.

Findings

Water emission is blue-shifted and extends over ~500 AU.

Emission likely originates from protostellar jet or wind.

Results suggest water observations include wind or jet components.

Abstract

Using the Submillimeter Array (SMA) on Mauna Kea, the H2-16O 10_2,9-9_3,6 transition (E_up=1863K) at 321.2 GHz has been detected toward the embedded low-mass protostar HL Tau. The line centroid is blue-shifted by 15 km/s with respect to the source velocity, and it has a FWHM of 20 km/s. The emission is tentatively resolved and extends ~3-4" over the sky (~2 beams), or ~500 AU at the distance of Taurus. The velocity offset, and to a lesser degree the spatial extent of the emission, shows that the line originates in the protostellar jet or wind. This result suggests that at least some water emission observed toward embedded sources, and perhaps also disk sources, with Herschel and Spitzer contains a wind or jet component, which is crucial for interpreting these data. These pathfinder observations done with the SMA opens a new window to studying the origin of water emission with e.g. ALMA, thus providing new insights into where water is in protostellar systems.