Issue |
A&A
Volume 390, Number 1, July IV 2002
|
|
---|---|---|
Page(s) | 187 - 198 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361:20020687 | |
Published online | 05 July 2002 |
First Stars II. Elemental abundances in the extremely metal-poor star CS 22949–037 *
A diagnostic of early massive supernovae
1
Observatoire de Paris-Meudon, GEPI, 92195 Meudon Cedex, France e-mail: Vanessa.Hill@obspm.fr, Roger.Cayrel@obspm.fr e-mail: Monique.Spite@obspm.fr, Francois.Spite@obspm.fr, Patrick.Francois@obspm.fr
2
GRAAL, Université de Montpellier II, 34095 Montpellier Cedex 05, France e-mail: Bertrand.Plez@graal.univ-montp2.fr
3
Department of Physics & Astronomy, Michigan State University, East Lansing, MI 48824, USA e-mail: beers@pa.msu.edu
4
IAG, Universidade de São Paulo, Departamento de Astronomia, CP 3386, 01060-970 São Paulo, Brazil e-mail: barbuy@astro.iag.usp.br
5
Astronomical Observatory, NBIfAFG, Juliane Maries Vej 30, 2100 Copenhagen, Denmark e-mail: ja@astro.ku.dk
6
Istituto Nazionale di Astrofisica – Osservatorio Astronomico di Trieste, Via G.B. Tiepolo 11, 34131 Trieste, Italy e-mail: bonifaci@ts.astro.it
7
Lund Observatory, Box 43, 221 00 Lund, Sweden e-mail: birgitta@astro.lu.se
8
European Southern Observatory (ESO), Karl-Schwarschild-Str. 2, 85749 Garching b. München, Germany e-mail: fprimas@eso.org
Corresponding author: E. Depagne, Eric.Depagne@obspm.fr
Received:
14
February
2002
Accepted:
3
May
2002
CS 22949–037 is one of the most metal-poor giants known
(), and it exhibits large overabundances of carbon
and nitrogen (Norris et al.). Using
VLT-UVES spectra of unprecedented quality, regarding resolution and
ratio, covering a wide wavelength range (from
to
900 nm), we have determined abundances for 21 elements in this star
over a wide range of atomic mass. The major new discovery is an
exceptionally large oxygen enhancement,
, as
measured from the [O I] line at 630.0 nm. We find an enhancement of
[N/Fe] of
, and a milder one of
,
similar to those already reported in the literature. This implies
.
We also find carbon isotopic
ratios 12C/13C
and 13C/
, close to the equilibrium value of the CN cycle.
Lithium is not detected. Na is strongly enhanced (
),
while S and K are not detected. The silicon-burning elements
Cr and Mn are underabundant, while Co and Zn are overabundant
(
). Zn is measured for the first time in such an
extremely metal-poor star. The abundances of the neutron-capture
elements Sr, Y, and Ba are strongly decreasing with the atomic number of the
element:
,
, and
. Among possible progenitors of CS 22949–037, we
discuss the pair-instability supernovae. Such very massive objects
indeed produce large amounts of oxygen, and have been found to be
possible sources of primary nitrogen. However, the predicted odd/even
effect is too large, and the predicted Zn abundance much too low.
Other scenarios are also discussed. In particular, the yields of a
recent model (Z35Z) from Heger and Woosley are shown to be in fair agreement with
the observations. The only discrepant prediction is the very low
abundance of nitrogen, possibly curable by taking into account other
effects such as rotationally induced mixing. Alternatively, the
absence of lithium in our star, and the values of the isotopic ratios
12C/13C and 13C/14N close to the equilibrium value
of the CN cycle, suggest that the CNO abundances now observed might
have been altered by nuclear processing in the star itself. A
30–
supernova, with fallback,
seems the most likely progenitor
for CS 22949–037.
Key words: stars: fundamental parameters / stars: abundances / stars: individual: BPS CS 22949–037 / Galaxy: evolution
© ESO, 2002
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