SOFIA/EXES observations of warm H at high spectral resolution: witnessing para-to-ortho conversion behind a molecular shock wave in HH7
arXiv:1905.10381 · doi:10.3847/2041-8213/ab2249
Abstract
Spectrally-resolved observations of three pure rotational lines of H, conducted with the EXES instrument on SOFIA toward the classic bow shock HH7, reveal systematic velocity shifts between the S(5) line of ortho-H and the two para-H lines [S(4) and S(6)] lying immediately above and below it on the rotational ladder. These shifts, reported here for the first time, imply that we are witnessing the conversion of para-H to ortho-H within a shock wave driven by an outflow from a young stellar object. The observations are in good agreement with the predictions of models for non-dissociative, C-type molecular shocks. They provide a clear demonstration of the chemical changes wrought by interstellar shock waves, in this case the conversion of para-H to ortho-H in reactive collisions with atomic hydrogen, and provide among the most compelling evidence yet obtained for C-type shocks in which the flow velocity changes continuously.
19 pages, 4 figures. Accepted for publication in the Astrophysical Journal Letters
References in corpus (7)
- Spitzer observations of HH54 and HH7-11: mapping the H2 ortho-to-para ratio in shocked molecular gas
- Low velocity shocks: signatures of turbulent dissipation in diffuse irradiated gas
- Spitzer spectral line mapping of supernova remnants: I. Basic data and principal component analysis
- Models of irradiated molecular shocks
- CALYPSO view of SVS 13A with PdBI: Multiple jet sources
- First spectrally-resolved H observations towards HH 54 / Low HO abundance in shocks
- H emission from non-stationary magnetized bow shocks