Detection of Vibrationally Excited Co in Irc+10216

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 cm−3, 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.