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.
@article{arxiv.0811.4736,
title = {Detection of Vibrationally Excited CO in IRC+10216},
author = {Nimesh A. Patel and Ken H. Young and Sandra Brünken and Karl M. Menten and Patrick Thaddeus and Robert W. Wilson},
journal= {arXiv preprint arXiv:0811.4736},
year = {2015}
}