High spectral resolution observations toward Orion BN at 6 $\mu$m: no evidence for hot water

TL;DR

High spectral resolution observations of Orion BN at 6 μm reveal no evidence of hot water near BN, suggesting the absence of dense, warm gas in its immediate vicinity and informing its dynamical history.

Contribution

This study provides the first high-resolution spectral analysis near 6 μm of Orion BN, constraining the presence of hot water and informing models of its dynamical interactions.

Findings

No H₂O absorption or emission at BN's systemic velocity.

Detected H₂O absorption associated with foreground cool, dense gas.

Results favor scenarios without dense, warm gas close to BN.

Abstract

Orion BN has a large proper motion and radial velocity with respect to the gas and other stars in the region where it is presumed to have formed. Multiple dynamical interaction scenarios have been proposed to explain this motion. In one case BN is thought to have interacted with stars in the Trapezium cluster, while in another it is thought to have interacted with source I while deeply embedded in molecular gas. If there is dense gas that has been retained in close proximity to BN, it may be evidence that the latter scenario is favored. We observed BN at high spectral resolution in three windows near 6 $\mu$m using SOFIA/EXES targeting the $\nu_2$ vibrational band of H$_2$O. Absorption from only three transitions of H$_2$O is detected, and through kinematic analysis is associated with cool, dense foreground gas, not BN itself. We find no evidence for H$_2$O absorption or emission at the systemic velocity of BN.