2006A&A...455.1059M


C.D.S. - SIMBAD4 rel 1.7 - 2021.02.24CET19:12:56

2006A&A...455.1059M - Astronomy and Astrophysics, volume 455, 1059-1072 (2006/9-1)

CS 30322-023: an ultra metal-poor TP-AGB star?

MASSERON T., VAN ECK S., FAMAEY B., GORIELY S., PLEZ B., SIESS L., BEERS T.C., PRIMAS F. and JORISSEN A.

Abstract (from CDS):

The remarkable properties of CS 30322-023 became apparent during the course of a high-resolution spectroscopic study of a sample of 23 carbon-enhanced, metal-poor (CEMP) stars. This sample is studied in order to gain a better understanding of s- and r-process nucleosynthesis at low metallicity, and to investigate the role of duplicity. High-resolution UVES spectra have been obtained, and abundances are derived using 1-D, plane-parallel OSMARCS models under the LTE hypothesis. The derived atmospheric parameters and observed abundances are compared to evolutionary tracks and nucleosynthesis predictions to infer the evolutionary status of CS 30322-023. CS 30322-023 is remarkable in having the lowest surface gravity (logg≤-0.3) among the metal-poor stars studied to date. As a result of its rather low temperature (4100K), abundances could be derived for 35 chemical elements; the abundance pattern of CS 30322-023 is one of the most well-specified of all known extremely metal-poor stars. With [Fe/H]=-3.5, CS 30322-023 is the most metal-poor star to exhibit a clear s-process signature, and the most metal-poor ``lead star'' known. The available evidence indicates that CS 30322-023 is presently a thermally-pulsing asymptotic giant branch (TP-AGB) star, with no strong indication of binarity thus far (although a signal of period 192 d is clearly present in the radial-velocity data, this is likely due to pulsation of the stellar envelope). Low-mass TP-AGB stars are not expected to be exceedingly rare in a magnitude-limited sample such as the HK survey, because their high luminosities make it possible to sample them over a very large volume. The strong N overabundance and the low 12C/13C ratio (4) in this star is typical of the operation of the CN cycle. Coupled with a Na overabundance and the absence of a strong C overabundance, this pattern seems to imply that hot-bottom burning operated in this star, which should then have a mass of at least 2 M. However, the luminosity associated with this mass would put the star at a distance of about 50kpc, in the outskirts of the galactic halo, where no recent star formation is expected to have taken place. We explore alternative scenarios in which the observed abundance pattern results from some mixing mechanism yet to be identified occurring in a single low-metallicity 0.8M AGB star, or from pollution by matter from an intermediate-mass AGB companion which has undergone hot-bottom burning. We stress, however, that our abundances may be subject to uncertainties due to NLTE or 3D granulation effects which were not taken into consideration.

Abstract Copyright:

Journal keyword(s): stars: AGB and post-AGB - stars: carbon - stars: evolution - stars: individual: CS 30322-023 - Galaxy: halo

Simbad objects: 8

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Number of rows : 8

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 HE 0107-5240 Pe* 01 09 29.1554552993 -52 24 34.203535506   15.89 15.07 15.10 14.283 CEMP-no 230 0
2 BPS CS 30301-0015 Pe* 15 08 56.8433023195 +02 30 18.628172611   14.04 13.04   12.063 CEMP-s 44 0
3 V* V453 Oph RV* 17 26 49.1294964352 -02 23 36.433030709   11.7 10.85     A5 56 0
4 BPS CS 30314-0067 Pe* 20 52 50.9876997217 -34 19 40.549001966   12.98 11.85 11.175 10.583 CEMP-no 28 0
5 BPS CS 29498-0043 Pe* 21 03 52.1197489072 -29 42 50.344264361   14.8 13.72 13.013 12.406 CEMP-no 88 0
6 BPS CS 30322-0023 * 21 30 32.1818570433 -46 16 24.615679322   13.473 12.166 11.498 10.908 ~ 48 0
7 HE 2323-0256 Pe* 23 26 29.8073543039 -02 39 58.037206596   15.12 14.36   13.358 CEMP-no 172 0
8 HE 2356-0410 Pe* 23 59 13.1417869434 -03 53 48.220053208   14.39 13.60 13.164 12.713 CEMP-no 82 0

    Equat.    Gal    SGal    Ecl

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2021.02.24-19:12:56

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