The VLT MUSE NFM view of outflows and externally photoevaporating discs near the Orion Bar

TL;DR

This study uses VLT/MUSE observations to analyze externally photoevaporating discs near the Orion Bar, revealing the roles of FUV and EUV irradiation in driving disc winds and identifying new outflows.

Contribution

It provides detailed observational evidence of how different irradiation sources affect disc photoevaporation and clarifies the origins of specific outflows in the Orion region.

Findings

FUV irradiation drives mass loss in discs without EUV ionization.

203-504 shows classic proplyd morphology with EUV irradiation.

203-506 is irradiated by FUV but not EUV, affecting its outflow characteristics.

Abstract

We present VLT/MUSE Narrow Field Mode (NFM) observations of a pair of disc-bearing young stellar objects towards the Orion Bar: 203-504 and 203-506. Both of these discs are subject to external photoevaporation, where winds are launched from their outer regions due to environmental irradiation. Intriguingly, despite having projected separation from one another of only 1.65{\arcsec} (660au at 400pc), 203-504 has a classic teardrop shaped ``proplyd'' morphology pointing towards $\theta^2$Ori A (indicating irradiation by the EUV of that star, rather than $\theta^1$ Ori C) but 203-506 has no ionisation front, indicating it is not irradiated by stellar EUV at all. However, 203-506 does show [CI] 8727{\AA} and [OI] 6300{\AA} in emission, indicating irradiation by stellar FUV. This explicitly demonstrates the importance of FUV irradiation in driving mass loss from discs. We conclude that shielding of 203-506 from EUV is most likely due to its position on the observers side of an ionized layer lying in the foreground of the Huygens Region. We demonstrate that the outflow HH 519, previously thought to be emanating from 203-504 is actually an irradiated cloud edge and identify a new compact outflow from that object approximately along our line of sight with a velocity $\sim130$\,km\,s$^{-1}$.