2013/08/29 by C. Codella, S. Viti, C. Ceccarelli +8 · 1 citation
Physics and Astronomy · #Abundance (ecology) #Astro and Planetary Science #Astronomy and Astrophysical Research #Astrophysics and Star Formation Studies #Hyperfine structure #Interstellar medium #Line (geometry) #Shock (circulatory) #Shock wave #Spectral line #astro-ph.GA
paper · pdf · doi:10.1088/0004-637x/776/1/52
ApJ, in press
arxiv created 2013/08/29 · openalex publication_date 2013/09/25 · arxiv updated 2015/06/17 · openalex created_date 2019/06/27 · openalex updated_date 2026/08/05
We present the first detection of N 2 H + toward a low-mass protostellar outflow, namely, the L1157-B1 shock, at ∼0.1 pc from the protostellar cocoon. The detection was obtained with the IRAM 30 m antenna. We observed emission at 93 GHz due to the J = 1–0 hyperfine lines. Analysis of this emission coupled with HIFI CHESS multiline CO observations leads to the conclusion that the observed N 2 H + (1–0) line originated from the dense (⩾10 5 cm −3 ) gas associated with the large (20''–25'') cavities opened by the protostellar wind. We find an N 2 H + column density of a few 10 12 cm −2 corresponding to an abundance of (2–8) × 10 −9 . The N 2 H + abundance can be matched by a model of quiescent gas evolved for more than 10 4 yr, i.e., for more than the shock kinematical age (≃2000 yr). Modeling of C-shocks confirms that the abundance of N 2 H + is not increased by the passage of the shock. In summary, N 2 H + is a fossil record of the pre-shock gas, formed when the density of the gas was around 10 4 cm −3 , and then further compressed and accelerated by the shock.