2007A&A...473..871S


C.D.S. - SIMBAD4 rel 1.7 - 2020.02.20CET15:47:24

2007A&A...473..871S - Astronomy and Astrophysics, volume 473, 871-882 (2007/10-3)

The abundance of SiS in circumstellar envelopes around AGB stars.

SCHOEIER F.L., BAST J., OLOFSSON H. and LINDQVIST M.

Abstract (from CDS):

Given their photospheric origin and refractive nature, SiS molecules can provide major constraints on the relative roles of dust condensation and non-equilibrium processes in regulating the chemistry in circumstellar envelopes around evolved stars.New SiS multi-transition (sub-)millimetre line observations of a sample of AGB stars with varying photospheric C/O-ratios and mass-loss rates are presented. A combination of low- and high-energy lines are important in constraining the circumstellar distribution of SiS molecules. A detailed radiative transfer modelling of the observed SiS line emission is performed, including assessment of the effect of thermal dust grains in the excitation analysis. We find that the circumstellar fractional abundance of SiS in these environments has a strong dependence on the photospheric C/O-ratio as expected from chemical models. The carbon stars (C/O>1) have a mean fractional abundance of 3.1x10–6, about one order of magnitude higher than that found for the M-type AGB stars (C/O<1) where the mean value is 2.7x10–7. These numbers are in reasonable agreement with photospheric LTE chemical models. SiS appears to behave similarly to SiO in terms of photodissociation in the outer part of the circumstellar envelope. In contrast to previous results for the related molecule SiO, there is no strong correlation of the fractional abundance with density in the CSE, as would be the case if freeze-out onto dust grains were important. However, possible time-variability of the line emission in the lower J transitions and the sensitivity of the line emission to abundance gradients in the inner part of the CSE may mask a correlation with the density of the wind. There are indications that the SiS fractional abundance could be significantly higher closer to the star which, at least in the case of M-type AGB stars, would require non-equilibrium chemical processes.

Abstract Copyright:

Journal keyword(s): stars: AGB and post-AGB - stars: circumstellar matter - stars: late-type - stars: mass-loss

Simbad objects: 22

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Number of rows : 22

N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2020
#notes
1 V* KU And Mi* 00 06 52.7551927308 +43 05 02.356209801       14.12   M10 73 0
2 IRC +10011 OH* 01 06 25.9889735162 +12 35 52.890666456   20.7   18.26 14.01 M8 393 0
3 LEE 259 C* 03 26 29.5050382299 +47 31 48.463099623           N 165 0
4 V* U Cam C* 03 41 48.1762532767 +62 38 54.397016016   11.5 11.00     C-N5 230 0
5 V* IK Tau Mi* 03 53 28.8884898148 +11 24 21.865959095 16.99 17.03 13.39 7.29 3.20 M7-11 564 0
6 V* TX Cam Mi* 05 00 51.1569959503 +56 10 54.093107078       14.02   M9-9.5 326 0
7 IRC +50137 Mi* 05 11 19.4489549676 +52 52 33.222548186           M10 169 0
8 V* GX Mon OH* 06 52 47.0411386021 +08 25 19.131304542   15.40 15.46 10.56   M9 104 0
9 V* R Vol C* 07 05 36.2092864981 -73 00 52.021676008   14.24 8.70     Ce 77 0
10 RAFGL 4078 C* 07 45 02.4140089106 -71 19 45.852846228       15.92 12.72 C 44 0
11 IRC +10216 C* 09 47 57.40632 +13 16 43.5648     10.96     C9,5e 2115 0
12 V* RW LMi C* 10 16 02.2834693816 +30 34 18.977096332       15.27   C4,3e 378 0
13 RAFGL 4211 C* 15 11 41.4387312231 -48 19 58.763122448           C-rich 46 0
14 WOS 48 C* 15 23 05.0744336371 -51 25 58.881494593   17.85 16.66 14.51 10.18 C 117 1
15 IRC +20370 C* 18 41 54.5507538243 +17 41 08.481183828       13.56   C7,3e 107 0
16 IRC -10529 OH* 20 10 27.8733409252 -06 16 13.757843352         15.49 M: 130 0
17 V* V Cyg C* 20 41 18.2688237607 +48 08 28.886946369   14.05 7.70     C7,4eJ 290 0
18 V* RV Aqr C* 21 05 51.7378981699 -00 12 42.121668132     11.5     C6,3e 95 0
19 V* S Cep C* 21 35 12.8240104870 +78 37 28.201592479   12.13 7.40     C7,3e 245 0
20 RAFGL 3068 C* 23 19 12.60744 +17 11 33.1332           C 247 0
21 IRC +40540 C* 23 34 27.5215563443 +43 33 01.299562617     15.12     C8,3.5eJ 170 0
22 V* R Cas Mi* 23 58 24.8700291935 +51 23 19.691977266 6.71 6.63 4.80     M6.5-9e 674 0

    Equat.    Gal    SGal    Ecl

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2020.02.20-15:47:24

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