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

Abstract

We present high angular resolution observations of HC${}_3$N J=5--4 line and 7 mm continumm emission from the extreme carbon star CIT 6. We find that the 7 mm continuum emission is unresolved and has a flux consistent with black-body 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: (i) a faint outer shell that is nearly spherical which has a radius of 8\arcsec; and (ii) 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\arcsec. Our observations therefore suggest that the mass loss from CIT 6 is strongly modulated with time and highly anisotropic. Furthermore, a comparison between the data and our excitation modelling results suggests an unusually high abundance of HC${}_3$N in its envelope. 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.

23 pages, 5 figures, submitted to the Astrophysical Journal

References in corpus (5)

• Near-Infrared Photometry of Carbon Stars
• Imaging the circumstellar envelopes of AGB stars
• A spectral line survey in the 2 mm and 1.3 mm windows toward the carbon rich envelope of IRC +10216
• The Formation of Crystalline Dust in AGB Winds from Binary Induced Spiral Shocks
• Molecular shells in IRC+10216: Evidence for non-isotropic and episodic mass loss enhancement

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