Detection of OH toward the Extreme Carbon Star IRC +10216

We report the detection of the 1665 and 1667 MHz main lines of OH (hydroxyl) and upper limits on the 1612 MHz satellite line of OH toward the carbon-rich AGB star IRC +10216. We find a beam-averaged fractional abundance x (OH) ~ 4 × 10 -8 . This detection supports the identification by Melnick et al. of the 1 10 -1 01 transition of water vapor with a 556.936 GHz rest-frequency emission feature detected toward IRC +10216, since OH is the expected photodissociation product of water vapor. The shape of the OH lines, however, differs significantly from the shape expected on the basis of the observations of Melnick et al. Possible explanations for the anomalous shapes of the 1665 and 1667 MHz lines are discussed. The most likely explanations for the unexpected OH line shapes are either masing or an asymmetric distribution of OH molecules around IRC +10216.