Advanced

First stars X. The nature of three unevolved carbon-enhanced metal-poor stars

Sivarani, T.; Beers, T. C.; Bonifacio, P.; Molaro, P.; Cayrel, R.; Herwig, F.; Spite, M.; Spite, F.; Plez, B. and Andersen, J., et al. (2006) In Astronomy & Astrophysics 459(1). p.125-135
Abstract
Context. On the order of 20% of the very metal-poor stars in the Galaxy exhibit large carbon enhancements. It is important to establish which astrophysical sites and processes are responsible for the elemental abundance patterns of this early Galactic population. Aims. We seek to understand the nature of the progenitors of three main-sequence turnoff Carbon-Enhanced Metal-Poor (CEMP) stars, CS 31080-095, CS 22958-042, and CS 29528-041, based on a detailed abundance analysis. Methods. From high-resolution VLT/UVES spectra (R similar to 43 000), we determine abundances or upper limits for Li, C, N, O, and other important elements, as well as C-12/C-13 isotopic ratios. Results. All three stars have -3.30 <= [Fe/H]<= -2.85 and moderate... (More)
Context. On the order of 20% of the very metal-poor stars in the Galaxy exhibit large carbon enhancements. It is important to establish which astrophysical sites and processes are responsible for the elemental abundance patterns of this early Galactic population. Aims. We seek to understand the nature of the progenitors of three main-sequence turnoff Carbon-Enhanced Metal-Poor (CEMP) stars, CS 31080-095, CS 22958-042, and CS 29528-041, based on a detailed abundance analysis. Methods. From high-resolution VLT/UVES spectra (R similar to 43 000), we determine abundances or upper limits for Li, C, N, O, and other important elements, as well as C-12/C-13 isotopic ratios. Results. All three stars have -3.30 <= [Fe/H]<= -2.85 and moderate to high CNO abundances. CS 22958-042 is one of the most carbon-rich CEMP stars known ([C/Fe] = +3.2), while CS 29528-041 (one of the few N-enhanced metal-poor stars known) is one of the most nitrogen rich ([N/Fe] = +3.0). Oxygen is very high in CS 31080-095 ([O/Fe] = +2.35) and in CS 22958-042 ([O/Fe] = +1.35). All three stars exhibit [Sr/Fe] < 0; Ba is not detected in CS 22958-042 ([Ba/Fe] < -0.53),but it is moderately enhanced ([Ba/Fe] similar to 1) in the other two stars. CS 22958-042 displays one of the largest sodium overabundances yet found in CEMP stars ([Na/Fe] = +2.8). CS 22958-042 has C-12/C-13 = 9, similar to most other CEMP stars without enhanced neutron-capture elements, while C-12/C-13 = 40 in CS 31080-095. CS 31080-095 and CS 29528-041 have A(Li) similar to 1.7, below the Spite Plateau, while Li is not detected in CS 22958-042. Conclusions. CS 22958-042 is a CEMP-no star, but the other two stars are in no known class of CEMP star and thus either constitute a new class or are a link between the CEMP-no and CEMP-s classes, adding complexity to the abundance patterns for CEMP stars. We interpret the abundance patterns in our stars to imply that current models for the presumed AGB binary progenitors lack an extra-mixing process, similar to those apparently operating in RGB stars. (Less)
Please use this url to cite or link to this publication:
author
, et al. (More)
(Less)
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
stars :, Galaxy : abundances, stars : abundances, stars : population II, AGB and post AGB
in
Astronomy & Astrophysics
volume
459
issue
1
pages
125 - 135
publisher
EDP Sciences
external identifiers
  • wos:000241789100016
  • scopus:33750720345
ISSN
0004-6361
DOI
10.1051/0004-6361:20065440
language
English
LU publication?
yes
id
6bd08cf6-ff45-4941-9211-7ba8cdc0d28f (old id 378513)
date added to LUP
2007-10-19 10:14:26
date last changed
2019-06-04 02:24:28
@article{6bd08cf6-ff45-4941-9211-7ba8cdc0d28f,
  abstract     = {Context. On the order of 20% of the very metal-poor stars in the Galaxy exhibit large carbon enhancements. It is important to establish which astrophysical sites and processes are responsible for the elemental abundance patterns of this early Galactic population. Aims. We seek to understand the nature of the progenitors of three main-sequence turnoff Carbon-Enhanced Metal-Poor (CEMP) stars, CS 31080-095, CS 22958-042, and CS 29528-041, based on a detailed abundance analysis. Methods. From high-resolution VLT/UVES spectra (R similar to 43 000), we determine abundances or upper limits for Li, C, N, O, and other important elements, as well as C-12/C-13 isotopic ratios. Results. All three stars have -3.30 &lt;= [Fe/H]&lt;= -2.85 and moderate to high CNO abundances. CS 22958-042 is one of the most carbon-rich CEMP stars known ([C/Fe] = +3.2), while CS 29528-041 (one of the few N-enhanced metal-poor stars known) is one of the most nitrogen rich ([N/Fe] = +3.0). Oxygen is very high in CS 31080-095 ([O/Fe] = +2.35) and in CS 22958-042 ([O/Fe] = +1.35). All three stars exhibit [Sr/Fe] &lt; 0; Ba is not detected in CS 22958-042 ([Ba/Fe] &lt; -0.53),but it is moderately enhanced ([Ba/Fe] similar to 1) in the other two stars. CS 22958-042 displays one of the largest sodium overabundances yet found in CEMP stars ([Na/Fe] = +2.8). CS 22958-042 has C-12/C-13 = 9, similar to most other CEMP stars without enhanced neutron-capture elements, while C-12/C-13 = 40 in CS 31080-095. CS 31080-095 and CS 29528-041 have A(Li) similar to 1.7, below the Spite Plateau, while Li is not detected in CS 22958-042. Conclusions. CS 22958-042 is a CEMP-no star, but the other two stars are in no known class of CEMP star and thus either constitute a new class or are a link between the CEMP-no and CEMP-s classes, adding complexity to the abundance patterns for CEMP stars. We interpret the abundance patterns in our stars to imply that current models for the presumed AGB binary progenitors lack an extra-mixing process, similar to those apparently operating in RGB stars.},
  author       = {Sivarani, T. and Beers, T. C. and Bonifacio, P. and Molaro, P. and Cayrel, R. and Herwig, F. and Spite, M. and Spite, F. and Plez, B. and Andersen, J. and Barbuy, B. and Depagne, E. and Hill, V. and Francois, P. and Nordström, Birgitta and Primas, F.},
  issn         = {0004-6361},
  keyword      = {stars :,Galaxy : abundances,stars : abundances,stars : population II,AGB and post AGB},
  language     = {eng},
  number       = {1},
  pages        = {125--135},
  publisher    = {EDP Sciences},
  series       = {Astronomy & Astrophysics},
  title        = {First stars X. The nature of three unevolved carbon-enhanced metal-poor stars},
  url          = {http://dx.doi.org/10.1051/0004-6361:20065440},
  volume       = {459},
  year         = {2006},
}