2019A&A...628A..62M


Query : 2019A&A...628A..62M

2019A&A...628A..62M - Astronomy and Astrophysics, volume 628A, 62-62 (2019/8-1)

Study of CS, SiO, and SiS abundances in carbon star envelopes: assessing their role as gas-phase precursors of dust.

MASSALKHI S., AGUNDEZ M. and CERNICHARO J.

Abstract (from CDS):


Aims. We aim to determine the abundances of CS, SiO, and SiS in a large sample of carbon star envelopes covering a wide range of mass loss rates to investigate the potential role that these molecules could play in the formation of dust in the surroundings of the central AGB star.
Methods. We surveyed a sample of 25 carbon-rich AGB stars in the λ 2mm band, more concretely in the J=3-2 line of CS and SiO, and in the J=7-6 and J=8-7 lines of SiS, using the IRAM 30 m telescope. We performed excitation and radiative transfer calculations based on the large velocity gradient (LVG) method to model the observed lines of the molecules and to derive their fractional abundances in the observed envelopes. We also assessed the effect of infrared pumping in the excitation of the molecules. Results. We detected CS in all 25 targeted envelopes, SiO in 24 of them, and SiS in 17 sources. Remarkably, SiS is not detected in any envelope with a mass loss rate below 10–6M/yr while it is detected in all envelopes with mass loss rates above that threshold. We found that CS and SiS have similar abundances in carbon star envelopes, while SiO is present with a lower abundance. We also found a strong correlation in which the denser the envelope, the less abundant are CS and SiO. The trend is however only tentatively seen for SiS in the range of high mass loss rates. Furthermore, we found a relation in which the integrated flux of the MgS dust feature at 30µm increases as the fractional abundance of CS decreases.Conclusions. The decline in the fractional abundance of CS with increasing density could be due to gas-phase chemistry in the inner envelope or to adsorption onto dust grains. The latter possibility is favored by a correlation between the CS fractional abundance and the 30µm feature, which suggests that CS is efficiently incorporated onto MgS dust around C-rich AGB stars. In the case of SiO, the observed abundance depletion with increasing density is most likely caused by an efficient incorporation onto dust grains. We conclude that CS, SiO (very likely), and SiS (tentatively) are good candidates to act as gas-phase precursors of dust in C-rich AGB envelopes.

Abstract Copyright: © ESO 2019

Journal keyword(s): astrochemistry - molecular processes - stars: abundances - stars: AGB and post-AGB - circumstellar matter

VizieR on-line data: <Available at CDS (J/A+A/628/A62): list.dat spectra.fits>

Simbad objects: 27

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Number of rows : 27
N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2021
#notes
1 RAFGL 67 C* 00 27 41.1344625085 +69 38 51.613056614       18.4   C-rich 36 1
2 RAFGL 190 C* 01 17 51.378 +67 13 53.34           C-rich 66 0
3 LEE 259 C* 03 26 29.5050382299 +47 31 48.463099623           N 170 0
4 V* U Cam C* 03 41 48.1762532767 +62 38 54.397016016   11.5 11.00     C-N5 235 0
5 V* IK Tau Mi* 03 53 28.8884898148 +11 24 21.865959095 16.99 17.03 13.39 7.29 3.20 M7-11 590 0
6 V* GY Cam C* 04 35 17.5584381137 +62 16 23.759864277           C-rich 56 0
7 V* ST Cam C* 04 51 13.3478339517 +68 10 07.646494913   9.77 9.20     C-N5 139 0
8 V* R Lep C* 04 59 36.3480393629 -14 48 22.511432606 15.06 13.51 7.76 4.90 3.42 C7,6e 321 0
9 V* W Ori C* 05 05 23.7201883024 +01 10 39.459119918 16.36 9.52 6.10 3.83 2.35 C-N5 279 0
10 V* S Aur C* 05 27 07.4588448362 +34 08 58.844765355   13.48 8.20     C-N5+ 120 0
11 V* V636 Mon C* 06 25 01.4312710669 -09 07 15.961984234       11.78 8.83 C-N5 50 0
12 V* UU Aur C* 06 36 32.8375658812 +38 26 43.833646997   7.89 5.25 3.31 1.90 C-N5- 293 1
13 HD 56126 pA* 07 16 10.2589670319 +09 59 47.953674864   9.20 8.32     F0/5Ia 308 0
14 IRC +10216 C* 09 47 57.40632 +13 16 43.5648     10.96     C9,5e 2199 0
15 V* RW LMi C* 10 16 02.2834693816 +30 34 18.977096332       15.27   C4,3e 384 0
16 V* Y CVn C* 12 45 07.8257032577 +45 26 24.898861195 14.03 7.41 4.87 3.12 1.74 C-N5 464 0
17 IRC +20370 C* 18 41 54.5507538243 +17 41 08.481183828       13.56   C7,3e 112 0
18 V* V Aql C* 19 04 24.1548619887 -05 41 05.434251344   11.09 6.90     C-N5 207 0
19 IRC +30374 C* 19 34 10.0589829331 +28 04 08.361303564       16.22   C 76 0
20 RAFGL 2477 S* 19 56 48.4420056358 +30 44 02.609739938   17.9 14.8 14.1   M6SIII 54 1
21 RAFGL 2494 C* 20 01 09.0488458825 +40 55 39.036558501           C 65 0
22 RAFGL 2513 C* 20 09 14.2446480503 +31 25 44.893244193           C-rich 47 0
23 V* V Cyg C* 20 41 18.2688237607 +48 08 28.886946369   14.05 7.70     C7,4eJ 296 0
24 V* RV Aqr C* 21 05 51.7378981699 -00 12 42.121668132     11.5     C6,3e 99 0
25 V* S Cep C* 21 35 12.8240104870 +78 37 28.201592479   12.13 7.40     C7,3e 252 0
26 RAFGL 3068 C* 23 19 12.60744 +17 11 33.1332           C 257 0
27 IRC +40540 C* 23 34 27.5215563443 +43 33 01.299562617     15.12     C8,3.5eJ 173 0

    Equat.    Gal    SGal    Ecl

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2021.07.27-01:52:50

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