The ALMA Early Science View of FUor/EXor objects. II. The Very Wide Outflow Driven by HBC 494

TL;DR

This paper presents ALMA observations of the HBC 494 outflow, revealing the widest known outflow cavities in a Class I object, and discusses how wind-driven processes influence disc evolution.

Contribution

It provides detailed ALMA data on HBC 494's outflow and envelope, highlighting the extremely wide outflow cavities and supporting wind-driven models of disc evolution.

Findings

The outflow cavity has an opening angle of approximately 150 degrees.

The outflow mass is estimated to be around 0.1 solar masses.

The morphology suggests interaction between inner disc winds and the envelope.

Abstract

We present Atacama Large Millimeter/sub-millimeter Array (ALMA) Cycle-2 observations of the HBC 494 molecular outflow and envelope. HBC 494 is an FU Ori-like object embedded in the Orion A cloud and is associated with the reflection nebulae Re50 and Re50N. We use $^{12}$CO, $^{13}$CO and C$^{18}$O spectral line data to independently describe the outflow and envelope structures associated with HBC 494. The moment-1 map of the $^{12}$CO emission shows the widest outflow cavities in a Class I object known to date (opening angle $\sim$ 150$^{^{\circ}}$). The morphology of the wide outflow is likely to be due to the interaction between winds originating in the inner disc and the surrounding envelope. The low-velocity blue- and red-shifted $^{13}$CO and C$^{18}$O emission trace the rotation and infall motion of the circumstellar envelope. Using molecular line data and adopting standard methods for correcting optical depth effects, we estimate its kinematic properties, including an outflow mass on the order of 10$^{-1}$ M$_{\odot}$. Considering the large estimated outflow mass for HBC 494, our results support recent theoretical work suggesting that wind-driven processes might dominate the evolution of protoplanetary discs via energetic outflows.