Uncovering the Outflow Driven by the Brown Dwarf LS-RCr A1: H-alpha as a Tracer of Outflow Activity in Brown Dwarfs

TL;DR

This paper confirms outflow activity in a young brown dwarf using spectro-astrometry, revealing that H-alpha emission traces outflows and challenging its use as a sole indicator of accretion, while also suggesting disk features related to planet formation.

Contribution

It demonstrates that H-alpha emission in brown dwarfs can originate from outflows, not just accretion, and provides new insights into disk structure and outflow detection methods.

Findings

Confirmed outflow origin of forbidden lines in LS-RCrA 1

Discovered H-alpha line traces outflows in brown dwarfs

Indicated presence of a dust hole in the accretion disk

Abstract

It is now apparent that classical T Tauri-like outflows commonly accompany the formation of young brown dwarfs. To date two optical outflows have been discovered and results presented in this paper increase this number to three. Using spectro-astrometry the origin of the LS-RCrA 1 forbidden emission lines in a blue-shifted outflow is confirmed. The non-detection of the red-shifted component of the outflow in forbidden lines, along with evidence for some separation between low and high velocity outflow components, do not support the hypothesis that LS-RCrA 1 has an edge-on accretion disk. The key result of this analysis is the discovery of an outflow component to the H-alpha line. The H-alpha line profile has blue and red-shifted features in the wings which spectro-astrometry reveals to also originate in the outflow. The discovery that H-alpha emission in BDs can have a significant contribution from an outflow suggests the use of H-alpha line widths as a proxy of mass accretion in BDs is not clear-cut. This method assumes that any contribution to the H-alpha line flux from a possible outflow is negligible. Finally the fact that the H-alpha line traces both lobes of the outflow while only the blue-shifted lobe is seen in forbidden emission points to the presence of a dust hole in the accretion disk of LS-RCrA 1. This is commonly seen in CTTSs and is assumed to signal the onset of planet formation.