Tracing the asymmetry in the envelope around the carbon star cit 6

Abstract

We present high angular resolution observations of HC3N 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 HC3N J = 5 - 4 line emission originates from an asymmetric and clumpy expanding envelope comprising two separate shells of HC3N 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 HC3N 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 HC3N may be enhanced in spiral shocks produced by the interaction between the circumstellar envelope of CIT 6 and its companion star. © 2009 The American Astronomical Society.