Vibrationally Excited Molecular Hydrogen Near Herschel 36

Abstract

We present the first high resolution UV spectra toward Herschel 36, a Trapezium-like system of high-mass stars contained within the Lagoon Nebula (M8, NGC 6523). The spectra reveal extreme ro-vibrational excitation of molecular hydrogen in material at a single velocity or very small range of velocities, with this component presumably lying near the star system and undergoing fluorescent excitation. The overall H${}_2$ excitation is similar to, but apparently larger than, that seen towards HD 37903 which previously showed the largest vibrationally excited H${}_2$ column densities seen in UV absorption spectra. While the velocities of the highly excited H${}_2$ lines are consistent within each observation, it appears that they underwent a $\sim$60 km s${}^{-1}$ redshift during the 3.6 years between observations. In neither case does the velocity of the highly excited material match the velocity of the bulk of the line-of-sight material which appears to mostly be in the foreground of M8. Recent work shows unusually excited CH and CH${}^{+}$ lines and several unusually broad Diffuse Interstellar Bands towards Herschel 36. Along with the H${}_2$ excitation, all of these findings appear to be related to the extreme environment within $\sim$0.1 pc of the massive young stellar system.

11 pages, 11 figures, accepted for publication in ApJ

References in corpus (7)

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