Detection of Vibrationally Excited CO in IRC+10216

TL;DR

This paper reports the detection of vibrationally excited CO molecules near the star IRC+10216, revealing high-temperature conditions and dense gas close to the stellar photosphere, which challenges existing models.

Contribution

First detection of vibrationally excited CO in IRC+10216, providing new insights into the physical conditions near the star's photosphere.

Findings

Detected vibrationally excited CO J=3-2 and 2-1 lines

Emission originates from a very small region close to the star

Gas density required for excitation exceeds previous model predictions

Abstract

Using the Submillimeter Array we have detected the J=3-2 and 2-1 rotational transitions from within the first vibrationally excited state of CO toward the extreme carbon star IRC+10216 (CW Leo). The emission remains spatially unresolved with an angular resolution of ~2" and, given that the lines originate from energy levels that are ~3100 K above the ground state, almost certainly originates from a much smaller (~10^{14} cm) sized region close to the stellar photosphere. Thermal excitation of the lines requires a gas density of ~10^{9} cm^{-3}, about an order of magnitude higher than the expected gas density based previous infrared observations and models of the inner dust shell of IRC+10216.