2018A&A...611A..29M


C.D.S. - SIMBAD4 rel 1.7 - 2019.11.19CET07:36:55

2018A&A...611A..29M - Astronomy and Astrophysics, volume 611A, 29-29 (2018/3-1)

Abundance of SiC2in carbon star envelopes. Evidence that SiC2is a gas-phase precursor of SiC dust.

MASSALKHI S., AGUNDEZ M., CERNICHARO J., VELILLA PRIETO L., GOICOECHEA J.R., QUINTANA-LACACI G., FONFRIA J.P., ALCOLEA J. and BUJARRABAL V.

Abstract (from CDS):


Context. Silicon carbide dust is ubiquitous in circumstellar envelopes around C-rich asymptotic giant branch (AGB) stars. However, the main gas-phase precursors leading to the formation of SiC dust have not yet been identified. The most obvious candidates among the molecules containing an Si-C bond detected in C-rich AGB stars are SiC2, SiC, and Si2C. To date, the ring molecule SiC2 has been observed in a handful of evolved stars, while SiC and Si2C have only been detected in the C-star envelope IRC +10216. Aim. We aim to study how widespread and abundant SiC2, SiC, and Si2C are in envelopes around C-rich AGB stars, and whether or not these species play an active role as gas-phase precursors of silicon carbide dust in the ejecta of carbon stars.
Methods. We carried out sensitive observations with the IRAM 30m telescope of a sample of 25 C-rich AGB stars to search for emission lines of SiC2, SiC, and Si2C in the λ 2mm band. We performed non-LTE excitation and radiative transfer calculations based on the LVG method to model the observed lines of SiC2 and to derive SiC2 fractional abundances in the observed envelopes.
Results. We detect SiC2 in most of the sources, SiC in about half of them, and do not detect Si2C in any source except IRC +10216. Most of these detections are reported for the first time in this work. We find a positive correlation between the SiC and SiC2 line emission, which suggests that both species are chemically linked; the SiC radical is probably the photodissociation product of SiC2 in the external layer of the envelope. We find a clear trend where the denser the envelope, the less abundant SiC2 is. The observed trend is interpreted as evidence of efficient incorporation of SiC2 onto dust grains, a process that is favored at high densities owing to the higher rate at which collisions between particles take place.
Conclusions. The observed behavior of a decline in the SiC2 abundance with increasing density strongly suggests that SiC2 is an important gas-phase precursor of SiC dust in envelopes around carbon stars.

Abstract Copyright: © ESO 2018

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

Simbad objects: 28

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Number of rows : 28

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 RAFGL 67 C* 00 27 41.1344625085 +69 38 51.613056614       18.4   C-rich 35 1
2 RAFGL 190 C* 01 17 51.378 +67 13 53.34           C-rich 66 0
3 * omi Cet Mi* 02 19 20.79210 -02 58 39.4956   7.63 6.53 5.03   M5-9IIIe+DA 1413 0
4 LEE 259 C* 03 26 29.5050382299 +47 31 48.463099623           N 165 0
5 V* U Cam C* 03 41 48.1762532767 +62 38 54.397016016   11.5 11.00     C-N5 230 0
6 V* GY Cam C* 04 35 17.5584381137 +62 16 23.759864277           C-rich 54 0
7 V* ST Cam C* 04 51 13.3478339517 +68 10 07.646494913   9.77 9.20     C-N5 135 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 312 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 271 0
10 V* S Aur C* 05 27 07.4588448362 +34 08 58.844765355   13.48 8.20     C-N5+ 116 0
11 V* V636 Mon C* 06 25 01.4312710669 -09 07 15.961984234       11.78 8.83 C-N5 48 0
12 V* UU Aur C* 06 36 32.8375658812 +38 26 43.833646997   7.89 5.25 3.31 1.90 C-N5- 288 1
13 V* VY CMa s*r 07 22 58.32877 -25 46 03.2355 12.01 10.19 7.95     M5Iae 984 0
14 IRC +10216 C* 09 47 57.406 +13 16 43.56     10.96     C9,5e 2107 0
15 V* RW LMi C* 10 16 02.2834693816 +30 34 18.977096332       15.27   C4,3e 377 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 459 0
17 IRC +20370 C* 18 41 54.5507538243 +17 41 08.481183828       13.56   C7,3e 107 0
18 V* V Aql C* 19 04 24.1548619887 -05 41 05.434251344   11.09 6.90     C-N5 201 0
19 IRC +30374 C* 19 34 10.0589829331 +28 04 08.361303564       16.22   C 75 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 63 0
22 RAFGL 2513 C* 20 09 14.2446480503 +31 25 44.893244193           C-rich 46 0
23 V* V Cyg C* 20 41 18.2688237607 +48 08 28.886946369   14.05 7.70     C7,4eJ 290 0
24 V* V1610 Cyg pA* 21 02 18.27 +36 41 37.0           F5Iae 825 1
25 V* RV Aqr C* 21 05 51.7378981699 -00 12 42.121668132     11.5     C6,3e 95 0
26 V* S Cep C* 21 35 12.8240104870 +78 37 28.201592479   12.13 7.40     C7,3e 245 0
27 RAFGL 3068 C* 23 19 12.607 +17 11 33.13           C 247 0
28 IRC +40540 C* 23 34 27.5215563443 +43 33 01.299562617     15.12     C8,3.5eJ 170 0

    Equat.    Gal    SGal    Ecl

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2019.11.19-07:36:55

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