2010/07/20 by S. Bruderer, A. O. Benz, E. F. van Dishoeck +75 · 2 citations
Chemistry · Physics and Astronomy · #Absorption (acoustics) #Absorption spectroscopy #Analytical Chemistry (journal) #Astronomy #Astrophysics #Astrophysics and Star Formation Studies #Atomic physics #Chemistry #Diatomic molecule #Excitation #Excited state #Infrared #Molecular Spectroscopy and Structure #Molecule #Optics #Physics #Spectral line #Stellar, planetary, and galactic studies #astro-ph.SR
paper · pdf · doi:10.1051/0004-6361/201015098
Accepted for publication in Astronomy and Astrophysics (HIFI first results issue)
arxiv created 2010/07/20 · openalex publication_date 2010/07/23 · arxiv updated 2015/05/19 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
The Heterodyne Instrument for the Far Infrared (HIFI) onboard the <i>Herschel<i/> Space Observatory allows the first observations of light diatomic molecules at high spectral resolution and in multiple transitions. Here, we report deep integrations using HIFI in different lines of hydrides towards the high-mass star forming region AFGL 2591. Detected are CH, CH<sup>+<sup/>, NH, OH<sup>+<sup/>, H<sub>2<sub/>O<sup>+<sup/>, while NH<sup>+<sup/> and SH<sup>+<sup/> have not been detected. All molecules except for CH and CH<sup>+<sup/> are seen in absorption with low excitation temperatures and at velocities different from the systemic velocity of the protostellar envelope. Surprisingly, the CH(<i>J<i/><sub><i>F,P<i/><sub/> = 3/2<sub>2,-<sub/> - 1/2<sub>1,+<sub/> ) and CH<sup>+<sup/>(<i>J<i/> = 1–0, <i>J<i/> = 2–1) lines are detected in emission at the systemic velocity. We can assign the absorption features to a foreground cloud and an outflow lobe, while the CH and CH<sup>+<sup/> emission stems from the envelope. The observed abundance and excitation of CH and CH<sup>+<sup/> can be explained in the scenario of FUV irradiated outflow walls, where a cavity etched out by the outflow allows protostellar FUV photons to irradiate and heat the envelope at larger distances driving the chemical reactions that produce these molecules.