2009A&A...508..909Z


C.D.S. - SIMBAD4 rel 1.7 - 2021.03.04CET20:52:51

2009A&A...508..909Z - Astronomy and Astrophysics, volume 508, 909-922 (2009/12-3)

The chemical composition of carbon stars. The R-type stars.

ZAMORA O., ABIA C., PLEZ B., DOMINGUEZ I. and CRISTALLO S.

Abstract (from CDS):

The aim of this work is to shed some light on the problem of the formation of carbon stars of R-type from a detailed study of their chemical composition. We use high-resolution and high signal-to-noise optical spectra of 23 R-type stars (both early- and late-types) selected from the Hipparcos catalogue. The chemical analysis is made using spectral synthesis in LTE and state-of-the-art carbon-rich spherical model atmospheres. We derive their CNO content (including the 12C/13C ratio), average metallicity, lithium, and light (Sr, Y, Zr) and heavy (Ba, La, Nd, Sm) s-element abundances. The observed properties of the stars (galactic distribution, kinematics, binarity, photometry and luminosity) are also discussed. Our analysis shows that late-R stars are carbon stars with identical chemical and observational characteristics as the normal (N-type) AGB carbon stars. The s-element abundance pattern derived can be reproduced by low-mass AGB nucleosynthesis models where the 13C(α, n)16O reaction is the main neutron donor. We confirm the results of the sole previous abundance analysis of early-R stars, namely that they are carbon stars with near solar metallicity showing enhanced nitrogen, low 12C/13C ratios and no s-element enhancements. In addition, we have found that early-R stars have Li abundances larger than expected for post RGB tip giants. We also find that a significant number (∼40 %) of the early-R stars in our sample are wrongly classified, probably being classical CH stars and normal K giants. On the basis of the chemical analysis, we confirm the previous suggestion that late-R stars are just misclassified N-type carbon stars in the AGB phase of evolution. Their photometric, kinematic, variability and luminosity properties are also compatible with this. In consequence, we suggest that the number of true R stars is considerably lower than previously believed. This alleviates the problem of considering R stars as a frequent stage in the evolution of low-mass stars. We briefly discuss the different scenarios proposed for the formation of early-R stars. The mixing of carbon during an anomalous He-flash is favoured, although no physical mechanism able to trigger that mixing has been found yet. The origin of these stars still remains a mystery.

Abstract Copyright:

Journal keyword(s): stars: abundances - stars: chemically peculiar - stars: carbon - stars: AGB and post-AGB

Simbad objects: 30

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Number of rows : 30

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 V* UV Aur C* 05 21 48.9137852435 +32 30 40.177257425   12.46 10.41 9.15   C8,1Je 199 0
2 HD 34842 ** 05 21 48.92 +32 30 39.8           C8,1Je+B9V 197 0
3 V* BM Gem C* 07 20 59.0073994508 +24 59 58.090785507     11.50     C-J5- 141 1
4 HD 57884 C* 07 23 06.9953471416 -04 12 48.792585986   11.7 9.0     C4+,3 39 0
5 V* NQ Gem Sy* 07 31 54.5215639809 +24 30 12.543689289   10.19 8.01     C6,2_CH3 91 0
6 C* 978 C* 08 00 12.2183391435 -04 45 28.452084499   13.16 11.21     C2:,2: 14 0
7 HD 78278 C* 09 07 57.1211668545 +21 35 12.814052900   12.11 10.59     C3,4J 26 0
8 BD+41 2150 Pe* 11 00 48.5529266718 +40 42 10.557451801   11.2 10.03     C3,1_CH3_Ba4 24 0
9 BD+71 600 Pe* 12 03 24.9815946000 +70 25 55.695015427   11.4 10.15     C2,3_CH4 26 0
10 V* RU Vir C* 12 47 18.4075712853 +04 08 41.364022128   14.75 9.00     C8,1e 167 0
11 HD 112127 C* 12 53 55.7454142679 +26 46 47.984571519 9.56 8.14 6.88 5.97 5.39 C-R4IIIb 142 0
12 HD 123821 C* 14 08 27.4530942087 +51 35 32.530258751   9.68 8.63     C-R2IIIa 33 0
13 BD+30 2637 Pe* 15 17 32.1334999390 +29 36 10.231110727   10.78 9.74     C3,0+_CH4 24 0
14 V* AG Dra Sy* 16 01 41.0125687664 +66 48 10.131181273 11.50 11.06 9.74 8.52   K3IIIep 479 0
15 NAME UKS-Ce1 Sy* 16 15 29.6279771715 -22 12 15.560438504       15.51 14.19 C4,5Je_CH4 29 0
16 BD+23 2998 C* 16 47 24.6712929288 +23 12 57.473419364 12.13 11.00 9.80 9.00 8.43 C-R3IIIa: 37 0
17 HD 156074 C* 17 13 31.2406466799 +42 06 22.767557235 9.67 8.75 7.61 6.89 6.42 C-R2III 118 0
18 BD+02 3336 C* 17 31 23.2569673760 +01 58 33.159188589 13.34 11.31 9.40 8.12 7.14 C-N5III: 44 0
19 BD+17 3325 Pe* 17 45 42.7802627066 +17 12 51.674961613 11.04 9.91 8.73 7.92 7.33 C2,0+_CH4: 31 0
20 HD 163838 C* 17 53 42.4856436618 +64 06 56.613885739   11.84 10.72     C2,2 27 0
21 HD 166097 C* 18 08 45.3981123679 +09 27 07.765482096 13.33 11.56 10.03 8.83 8.00 C3,5J 38 0
22 V* RV Sct C* 18 44 25.1719620626 -13 12 47.663588883   12.46 9.94     C-R4+ 33 0
23 HD 178316 C* 19 08 49.9621850716 -17 15 55.498461152   11.72 10.32     R2 20 0
24 Case 286 C* 19 24 36.2750968608 +30 39 07.766041176   12.06 10.67     C 15 0
25 HD 188934 C* 19 57 37.6203951199 +00 14 30.208070762 13.48 11.38 9.37 7.97 7.00 C3,1 32 0
26 BD+57 2161 Pe* 20 14 07.7503937767 +58 06 19.420419723   11.3 9.68     C4,1_CH3_Ba4 26 0
27 V* LW Cyg C* 21 55 13.7693675476 +50 29 49.739740954   13.39 12.30     C5,4e: 62 0
28 V* CT Lac C* 22 06 39.9283608006 +48 27 06.858851962   13.24 10.60     C6-,4 36 0
29 HD 216649 C* 22 54 46.4913001435 -06 57 50.624952657   11.96 10.75     R3 20 0
30 V* EU And C* 23 19 58.8815022082 +47 14 34.576375397   12.84 10.38     C-J5- 87 0

    Equat.    Gal    SGal    Ecl

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2021.03.04-20:52:51

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