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K. B. Marvel (American Astronomical Society)
I present observations of HCN associated with the oxygen-rich stars TX Cam and IK Tau. These observations were obtained with the Owens Valley Radio Observatory millimeter array telescope, funded in part by the National Science Foundation.
The distribution of HCN near these evolved stars is generally spherical in nature although mildly asymmetric. The emission is optically thick and therefore quantitative interpretation is difficult. It is clear from the images that the HCN is centrally peaked in every channel and clearly does not exist in a shell-like distribution. The overall diameter of the emission is about 750 AU for IK Tau and 940 AU for TX Cam, assuming distances of 260 pc (Loup et al. 1993) and 280 pc (Knapp et al. 1998) respectively.
How oxygen-rich stars can exhibit emission from carbon-based molecules has long challenged chemical models for these sources. Charnley et al. (1995) proposed a chemical model, which also predicted the presence of C2H and CH3OH in detectable quantities. Charnley et al. (1997) subsequently used the NRAO 12-m to show that these molecules do not exist in detectable quantities near these stars. I confirm this result using interferometric observations, which are more sensitive to compact distributions of gas.
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