1999/06/12 by Ronald Stark, Floris F. S. van der Tak, Ewine F. van Dishoeck · 2 citations
Physics and Astronomy · #Absorption (acoustics) #Abundance (ecology) #Astronomy and Astrophysical Research #Astrophysics and Star Formation Studies #Emission spectrum #Excitation #Excitation temperature #Interstellar medium #Line (geometry) #Spectral line #Stellar, planetary, and galactic studies #Young stellar object #astro-ph
paper · pdf · doi:10.1086/312182
Standard AAS LaTeX format (15 pages + 2 figures)
arxiv created 1999/06/12 · openalex publication_date 1999/08/10 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
We report the detection of the 1 10 -1 11 ground-state transition of ortho-H 2 D + at 372.421 GHz in emission from the young stellar object NGC 1333 IRAS 4A. Detailed excitation models with a power-law temperature and density structure yield a beam-averaged H 2 D + abundance of 3 × 10 -12 with an uncertainty of a factor of 2. The line was not detected toward W33A, GL 2591, and NGC 2264 IRS (in the latter source at a level that is 3-8 times lower than previous observations). The H 2 D + data provide direct evidence in support of low-temperature chemical models in which H 2 D + is enhanced by the reaction of H and HD. The H 2 D + enhancement toward NGC 1333 IRAS 4A is also reflected in the high DCO + /HCO + abundance ratio. Simultaneous observations of the N 2 H + 4-3 line show that its abundance is about 50-100 times lower in NGC 1333 IRAS 4A than in the other sources, suggesting significant depletion of N 2 . The N 2 H + data provide independent lower limits on the H abundance that are consistent with the abundances derived from H 2 D + . The corresponding limits on the H column density agree with recent near-infrared absorption measurements of H toward W33A and GL 2591.