2009ApJ...691L..55P

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 (∼10¹⁴ cm) sized region close to the stellar photosphere. Thermal excitation of the lines requires a gas density of ∼10⁹/cm3, about an order of magnitude higher than the expected gas density based on previous infrared observations and models of the inner dust shell of IRC+10216.