1998A&A...330..232F


C.D.S. - SIMBAD4 rel 1.7 - 2021.04.19CEST14:04:06

1998A&A...330..232F - Astronomy and Astrophysics, volume 330, 232-242 (1998/2-1)

Inferring acetylene abundances from C2H: the C2H2/HCN abundance ratio.

FUENTE A., CERNICHARO J. and OMONT A.

Abstract (from CDS):

We have carried out a survey of C2H and HCN in a wide sample of evolved stars using the 30-m IRAM telescope. Significant variations of the C2H abundance are found between the observed stars. Low C2H abundances, X(C2H)<10–5, are observed in S-stars, and detached envelopes. In massive C-rich stars ({dot}(M)>2x10–6M/yr) the C2H abundance seems to be correlated with the expansion velocity. Thus, the mean value of the C2H abundance is 1.2x10–5 in C-rich stars with Ve≤22km/s (hereafter ``low-Ve'' stars) and a factor of 5 larger, ∼5x10–5M/yr, in those with Ve≥22km/s (hereafter ``high-Ve'' stars). Some explanations are suggested to account for the large C2H abundances observed in ``high-Ve'' stars. The emission of the HCN lines is optically thick in most C-rich stars. The apparent variations of the HCN abundance with {dot}(M) and Ve are very likely due to an opacity effect. The most recent determination, based on ISO data, of the HCN abundance in IRC+10216 is X(HCN)∼3x10–5. From H13CN observations, we have obtained HCN abundances ranging from 3 to 30x10–5 in ``high-Ve'' stars. While HCN abundances ∼ 3x10–5 are found toward AFGL 809 and AFGL 2901 in agreement with the value found in IRC+10216, abundances ≥10–4 are estimated in IRC+00365, IRC+10401, IRC+30374 and S Cep. Based on our C2H data and assuming X(HCN)∼3x10–5 toward the prototypical star IRC+10216, we estimate a C2H2/HCN abundance ratio ∼ 1. The C2H2/HCN ratio in ``high-Ve'' stars ranges from ∼ 0.08 to 7. The large dispersion found in the HCN abundances toward ``high-Ve'' stars prevent us from detecting any systematic variation of the C2H2/HCN ratio with the expansion velocity in massive C-rich stars. In C-rich stars with low mass-loss rate, the C2H2/HCN ratio is a factor of 10 lower than in IRC+10216.

Abstract Copyright:

Journal keyword(s): stars: abundances - circumstellar matter - stars: AGB and post-AGB - radio lines: stars - stars: individual: IRC +10216

Simbad objects: 35

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Number of rows : 35

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 190 C* 01 17 51.378 +67 13 53.34           C-rich 66 0
2 V* R Scl C* 01 26 58.0946233986 -32 32 35.437732667 17.26 9.59 5.72 3.69 2.30 C-N5+ 304 0
3 LEE 259 C* 03 26 29.5050382299 +47 31 48.463099623           N 167 0
4 V* U Cam C* 03 41 48.1762532767 +62 38 54.397016016   11.5 11.00     C-N5 233 0
5 RAFGL 618 pA* 04 42 53.6245215366 +36 06 53.397219192   16.32   12.59   C-rich 964 0
6 RAFGL 809 C* 05 43 49.6869879023 +32 42 06.161816018           C-rich 61 0
7 RAFGL 865 C* 06 04 00.04728 +07 25 52.0104           C-rich 98 0
8 V* V477 Mon C* 06 29 35.4663563766 +08 47 16.388432068       15.2   C-rich 28 0
9 V* UU Aur C* 06 36 32.8375658812 +38 26 43.833646997   7.89 5.25 3.31 1.90 C-N5- 293 1
10 IRC +10216 C* 09 47 57.40632 +13 16 43.5648     10.96     C9,5e 2187 0
11 V* RW LMi C* 10 16 02.2834693816 +30 34 18.977096332       15.27   C4,3e 383 0
12 IRC -10236 C* 10 17 00.5764421884 -14 39 30.125586177       12.73 10.31 C 69 0
13 V* U Hya C* 10 37 33.2729535 -13 23 04.352923 13.29 7.51 4.82 3.05 1.78 C-N5 289 0
14 V* V Hya C* 10 51 37.2614060865 -21 15 00.339641553   12.23 6.80     C-N:6 344 0
15 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
16 WOS 48 C* 15 23 05.0744336371 -51 25 58.881494593   17.85 16.66 14.51 10.18 C 122 1
17 IRC +20370 C* 18 41 54.5507538243 +17 41 08.481183828       13.56   C7,3e 110 0
18 Case 176 C* 18 42 24.8714797393 -02 17 27.091013289   16.56 13.49 15.53 10.79 C 69 0
19 V* S Sct C* 18 50 20.0367524071 -07 54 27.430964220 13.93 9.89 6.80     C-N5 197 0
20 Case 181 C* 19 03 18.4246882324 +07 30 45.317950309     14.22 14.77   C 67 0
21 V* V Aql C* 19 04 24.1548619887 -05 41 05.434251344   11.09 6.90     C-N5 207 0
22 RAFGL 2333 C* 19 09 56.859 +09 26 51.43           C-rich 28 0
23 V* W Aql S* 19 15 23.3581458294 -07 02 50.308513461   12.72 10.14     S6/6e 209 0
24 IRC -10502 C* 19 20 18.1188934440 -08 02 12.080226785       13.22 10.59 C5,4e 67 0
25 IRC +30374 C* 19 34 10.0589829331 +28 04 08.361303564       16.22   C 76 0
26 V* TT Cyg C* 19 40 57.0159854799 +32 37 05.755486755   10.43 10.20     C-N5- 191 0
27 * chi Cyg S* 19 50 33.9243904 +32 54 50.609683 7.02 6.06 4.24 1.81 -0.01 S6-9/1-2e 670 0
28 V* V Cyg C* 20 41 18.2688237607 +48 08 28.886946369   14.05 7.70     C7,4eJ 295 0
29 RAFGL 2686 C* 20 59 09.5922788988 +27 26 38.604197392           C8-9,5eJ 50 1
30 V* V1610 Cyg pA* 21 02 18.27 +36 41 37.0           F5Iae 838 1
31 V* S Cep C* 21 35 12.8240104870 +78 37 28.201592479   12.13 7.40     C7,3e 249 0
32 RAFGL 2901 C* 22 25 53.4711422867 +60 20 43.600044109           C-rich 43 0
33 HD 235858 pA* 22 29 10.3755939027 +54 51 06.341145584   11.40 9.52 8.47 7.34 G5Ia 240 0
34 RAFGL 3068 C* 23 19 12.60744 +17 11 33.1332           C 256 0
35 IRC +40540 C* 23 34 27.5215563443 +43 33 01.299562617     15.12     C8,3.5eJ 172 0

    Equat.    Gal    SGal    Ecl

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2021.04.19-14:04:06

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