The abundance of 28Si32S, 29Si32S, 28Si34S, and 30Si32S in the inner layers of the envelope of IRC+10216

Abstract

We present high spectral resolution mid-IR observations of SiS towards the C-rich AGB star IRC+10216 carried out with the Texas Echelon-cross-Echelle Spectrograph mounted on the NASA Infrared Telescope Facility. We have identified 204 ro-vibrational lines of 28Si32S, 26 of 29Si32S, 20 of 28Si34S, and 15 of 30Si32S in the frequency range 720-790 cm-1. These lines belong to bands v=1-0, 2-1, 3-2, 4-3, and 5-4, and involve rotational levels with Jlow<90. About 30 per cent of these lines are unblended or weakly blended and can be partially or entirely fitted with a code developed to model the mid-IR emission of a spherically symmetric circumstellar envelope composed of expanding gas and dust. The observed lines trace the envelope at distances to the star <35R* (~0.7 arcsec). The fits are compatible with an expansion velocity of 1+2.5(r/R*-1) km/s between 1 and 5R*, 11 km/s between 5 and 20R*, and 14.5 km/s outwards. The derived abundance profile of 28Si32S with respect to H2 is 4.9e-6 between the stellar photosphere and 5R*, decreasing linearly to 1.6e-6 at 20R* and to 1.3e-6 at 50R*. 28Si32S seems to be rotationally under LTE in the region of the envelope probed with our observations and vibrationally out of LTE in most of it. There is a red-shifted emission excess in the 28Si32S lines of band v=1-0 that cannot be found in the lines of bands v=2-1, 3-2, 4-3, and 5-4. This excess could be explained by an enhancement of the vibrational temperature around 20R* behind the star. The derived isotopic ratios 28Si/29Si, and 32S/34S are 17 and 14, compatible with previous estimates.

11 pages, 5 figures, and 4 tables. Accepted for publication in MNRAS

References in corpus (18)

• Oxygen Chemistry in the Circumstellar Envelope of the Carbon-Rich Star IRC+10216
• Molecular abundances in the inner layers of IRC +10216
• A Detailed Analysis of the Dust Formation Zone of IRC+10216 Derived from Mid-IR Bands of C2H2 and HCN
• Discovery of SiCSi in IRC+10216: A missing link between gas and dust carriers of SiC bonds
• 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
• A spectral line survey in the 2 mm and 1.3 mm windows toward the carbon rich envelope of IRC +10216
• The abundance of SiS in circumstellar envelopes around AGB stars
• SiO in C-rich circumstellar envelopes of AGB stars: effects of non-LTE chemistry and grain adsorption
• Discovery of Time Variation of the Intensity of Molecular Lines in IRC+10216 in The Submillimeter and Far Infrared Domains
• Si-bearing molecules towards IRC+10216: ALMA unveils the molecular envelope of CWLeo
• An independent distance estimate to CW Leo
• The distribution of SiO in the circumstellar envelope around IRC+10216
• Discovery of multiple dust shells beyond 1 arcmin in the circumstellar envelope of IRC+10216 using Herschel/PACS
• On the physical structure of IRC+10216. Ground-based and Herschel observations of CO and CCH
• The complex dust formation zone of the AGB star IRC+10216 probed with CARMA 0.25 arcsec angular resolution molecular observations
• Herschel/HIFI observation of highly excited rotational lines of HNC toward IRC +10 216
• HST Images Reveal Dramatic Changes in the Core of IRC+10216

Cited by in corpus (11)

• Stellar yields from metal-rich asymptotic giant branch models
• IRC +10 216 in 3-D: morphology of a TP-AGB star envelope
• The abundance of C2H4 in the circumstellar envelope of IRC+10216
• Formation and destruction of SiS in space
• Carbon chemistry in IRC+10216: Infrared detection of diacetylene
• The maser emitting structure and time variability of the SiS lines J=14-13 and 15-14 in IRC+10216
• SiS in the circumstellar envelope of IRC +10126: maser and quasi-thermal emission
• Multi-frequency high spectral resolution observations of HCN toward the circumstellar envelope of Y CVn
• Detection of the S(1) Rotational Line of H2 toward IRC+10216: A Simultaneous Measurement of Mass-Loss Rate and CO Abundance
• New SiS destruction and formation routes via neutral-neutral reactions and their fundamental role in interstellar clouds at low and high metallicity values
• IRC+10216 mass loss properties through the study of $\lambda$3mm emission: Large spatial scale distribution of SiO, SiS, and CS