ALMA Observations of Vibrationally Excited HC 3 N Lines Toward Orion KL

Abstract

We present high spatial resolution ALMA observations of vibrational transitions of HC 3 N toward Orion KL in the 214–247 GHz frequency band. 41 transitions of HC 3 N in 7 vibrationally excited states, and 23 transitions of 13 C isotopologues of HC 3 N in 2 vibrational states are detected. The line images show that vibrationally excited HC 3 N lines originate mainly from the hot core of Orion and IRc7. The images of HC 3 N vibrationally excited lines show that the line emission peaks associated with the hot core move from south to northeast as increases. Based on multiple transitions of each vibrationally excited state, we performed local thermodynamic equilibrium calculations in the XCLASS suite toward the hot core and IRc7 positions. Generally, transitions in highly excited states have higher rotational temperatures and lower column densities. The rotational temperatures and column densities of the hot core range from 93 to 321 K, and from to cm −2 , respectively. Lower rotational temperatures ranging from 88 to 186 K and column densities from to cm −2 are obtained toward IRc7. The facts that the hot core emission peaks of vibrationally excited HC 3 N lines move from south to northeast with increasing , and that higher-energy HC 3 N lines have higher rotational temperatures and lower column densities, appear to support that the hot core is externally heated. The emission peaks are moving along the major axis of the SiO outflow, which may indicate that higher-energy HC 3 N transitions are excited by interaction between pre-existing dense medium and shocks generated by SiO outflows.