Molecular shells in IRC+10216: Evidence for non-isotropic and episodic mass loss enhancement

Abstract

We report high angular-resolution VLA observations of cyanopolyyne molecules HC${}_3$N and HC${}_5$N from the carbon rich circumstellar envelope of IRC+10216. The observed low-lying rotational transitions trace a much more extended emitting region than seen in previous observations at higher frequency transitions. We resolve the hollow quasi-spherical distribution of the molecular emissions into a number of clumpy shells. These molecular shells coincide spatially with dust arcs seen in deep optical images of the IRC+10216 envelope, allowing us to study for the first time the kinematics of these features. We find that the molecular and dust shells represent the same density enhancements in the envelope separated in time by $\sim$120 to $\sim$360 yrs. From the angular size and velocity spread of the shells, we estimate that each shell typically covers about 10% of the stellar surface at the time of ejection. The distribution of the shells seems to be random in space. The good spatial correspondance between HC${}_3$N and HC${}_5$N emissions is in qualitative agreement with a recent chemical model that takes into account the presence of density-enhanced shells. The broad spatial distribution of the cyanopolyyne molecules, however, would necessitate further study on their formation.

16 pages, 5 figures, accepted for publication in ApJ

References in corpus (2)

• The circumstellar envelope of IRC+10216 from milli-arcsecond to arcmin scales
• Radio continuum monitoring of the extreme carbon star IRC+10216

Cited by in corpus (16)

• The Dawes Review 2: Nucleosynthesis and stellar yields of low and intermediate-mass single stars
• Density-enhanced gas and dust shells in a new chemical model for IRC+10216
• Warm water vapour in the sooty outflow from a luminous carbon star
• ALMA data suggest the presence of a spiral structure in the inner wind of CW Leo
• Molecular shells in IRC+10216: tracing the mass loss history
• Discovery of multiple dust shells beyond 1 arcmin in the circumstellar envelope of IRC+10216 using Herschel/PACS
• Water in IRC+10216: a genuine formation process by shock-induced chemistry in the inner wind
• Photodissociation and chemistry of N${}_2$ in the circumstellar envelope of carbon-rich AGB stars
• The Role of Internal Photons on the Chemistry of the Circumstellar Envelopes of AGB Stars
• Tracing the asymmetry in the envelope around the carbon star CIT 6
• Investigating Anomalous Photochemistry in the Inner Wind of IRC+10216 Through Interferometric Observations of HC${}_3$N
• SiS in the circumstellar envelope of IRC +10126: maser and quasi-thermal emission
• Charting Circumstellar Chemistry of Carbon-rich AGB Stars: I. ALMA 3 mm spectral surveys
• Infrared color separation between thin-shelled oxygen-rich and carbon-rich AGB stars
• Detection of 4765 MHz OH Emission in a Pre-Planetary Nebula -- CRL 618
• Charting circumstellar chemistry of carbon-rich asymptotic giant branch stars. II. Abundances and spatial distributions of CS