Tracing the Asymmetry in the Envelope Around the Carbon Star Cit 6

We present high angular resolution observations of HC 3 N J = 5 − 4 line and 7 mm continuum emission from the extreme carbon star CIT 6. We find that the 7 mm continuum emission is unresolved and has a flux consistent with blackbody thermal radiation from the central star. The HC 3 N J = 5 − 4 line emission originates from an asymmetric and clumpy expanding envelope comprising two separate shells of HC 3 N J = 5 − 4 emission: (1) a faint outer shell that is nearly spherical which has a radius of 8'' and (2) a thick and incomplete inner shell that resembles a one-arm spiral starting at or close to the central star and extending out to a radius of about 5''. A comparison between the data and our excitation modeling results suggests an unusually high abundance of HC 3 N in the envelope of CIT 6. We discuss the possibility that the envelope might be shaped by the presence of a previously suggested possible binary companion. The abundance of HC 3 N may be enhanced in spiral shocks produced by the interaction between the circumstellar envelope of CIT 6 and its companion star.