Cyanoacetylene in the outflow/hot molecular core G331.512-0.103
N. U. Duronea ... [et al.].
Serie: Trabajos publicados del IAR ; no. 1557
Resumen: Using APEX-1 and APEX-2 observations, we have detected and studied therotational lines of the HC3N molecule (cyanoacetylene) in thepowerful outflow/hot molecular core G331.512-0.103. We identified 31rotational lines at J levels between 24 and 39; 17 of them in the groundvibrational state v = 0 (9 lines corresponding to the main Cisotopologue and 8 lines corresponding to the 13Cisotopologues), and 14 in the lowest vibrationally excited statev7 = 1. Using local thermodynamic equilibrium (LTE)-basedpopulation diagrams for the beam-diluted v = 0 transitions, wedetermined Texc = 85 ± 4 K and N(HC3N) = (6.9 ±0.8) × 1014 cm-2, while for the beam-dilutedv7 = 1 transitions we obtained Texc = 89 ± 10 Kand N(HC3N) = (2 ± 1) × 1015 cm-2. Non-LTE calculations using H2 collision rates indicate that theHC3N emission is in good agreement with LTE-based results.From the non-LTE method, we estimated Tkin ≃90 K,n(H2) ≃ 2 × 107 cm-3 for a central coreof 6 arcsec in size. A vibrational temperature in the range from 130 to145 K was also determined, values which are very likely lower limits.Our results suggest that rotational transitions are thermalized, whileinfrared radiative pumping processes are probably more efficient thancollisions in exciting the molecule to the vibrationally excited statev7 = 1. Abundance ratios derived under LTE conditions for the13C isotopologues suggest that the main formation pathway ofHC3N is C2H2 + CN â†' HC3N +H.
