2014A&A...571A..40S


C.D.S. - SIMBAD4 rel 1.7 - 2020.08.07CEST13:14:20

2014A&A...571A..40S - Astronomy and Astrophysics, volume 571A, 40-40 (2014/11-1)

The low Sr/Ba ratio on some extremely metal-poor stars.

SPITE M., SPITE F., BONIFACIO P., CAFFAU E., FRANCOIS P. and SBORDONE L.

Abstract (from CDS):

It has been noted that, in classical extremely metal-poor (EMP) stars, the abundance ratio of two well-observed neutron-capture elements, Sr and Ba, is always higher than [Sr/Ba]=-0.5, which is the value of the solar r-only process; however, a handful of EMP stars have recently been found with a very low Sr/Ba ratio. We try to understand the origin of this anomaly by comparing the abundance pattern of the elements in these stars and in the classical EMP stars. For a rigorous comparison with previous data, four stars with very low Sr/Ba ratios were observed and analyzed in the same way as in the First Stars program: analysis within LTE approximation through 1D (hydrostatic) model atmosphere, providing homogeneous abundances of nine neutron-capture elements. In CS 22950-173, the only turnoff star of the sample, the Sr/Ba ratio is, in fact, found to be higher than the r-only solar ratio, so the star is discarded. The remaining stars (CS 29493-090, CS 30322-023, HE 305-4520) are cool evolved giants. They do not present a clear carbon enrichment, but in evolved giants C is partly burned into N, and owing to their high N abundance, they could still have initially been carbon-rich EMP stars (CEMP). The abundances of Na to Mg present similar anomalies to those in CEMP stars. The abundance patterns of the neutron-capture elements in the three stars are strikingly similar to a theoretical s-process pattern. This pattern could at first be attributed to pollution by a nearby AGB, but none of the stars presents a clear variation in the radial velocity indicating the presence of a companion. The stellar parameters seem to exclude any internal pollution in a TP-AGB phase for at least two of these stars. The possibility that the stars are early-AGB stars polluted during the core He flash does not seem compatible with the theory.

Abstract Copyright:

Journal keyword(s): stars: abundances - stars: Population II - Galaxy: evolution - Galaxy: halo

VizieR on-line data: <Available at CDS (J/A+A/571/A40): linelist.dat>

CDS comments: BPS CS 22958-045 is a probable misprint.

Simbad objects: 12

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Number of rows : 12

N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2020
#notes
1 SKB 2 Pe* 00 41 39.8197261334 -26 18 54.463949137   13.338 12.221 11.704 11.321 C1,2 83 0
2 BPS CS 31082-0001 Pe* 01 29 31.1311330115 -16 00 45.496485322 12.527 12.427 11.642 11.189 10.713 CEMP 244 0
3 BPS CS 29528-0041 Pe* 02 29 25.2507036195 -18 13 28.042501354 14.83 15.20 14.59 14.67   CEMP-no 25 0
4 HE 0305-4520 Pe* 03 07 02.1830662441 -45 09 00.544178397   14.791 13.979 13.473 12.973 ~ 8 0
5 2MASS J04442200-4513542 C* 04 44 22.0060297382 -45 13 54.233994954 13.219 13.51 12.989 12.672 12.372 CEMP-s 22 0
6 HD 122563 Pe* 14 02 31.8456299772 +09 41 09.942736952 7.47 7.10 6.19 5.37 4.79 G8:III:Fe-5 748 0
7 BPS CS 22950-0173 PM* 20 35 31.2591932771 -15 53 30.716444601   14.45 14.04     ~ 14 0
8 BPS CS 30322-0023 * 21 30 32.1818570433 -46 16 24.615679322   13.473 12.166 11.498 10.908 ~ 47 0
9 HE 2134-3940 Pe* 21 37 45.7673672486 -39 27 22.314122762   13.790 12.660 12.160 11.760 KIIvw 81 0
10 HE 2156-3130 Pe* 21 59 05.7785371282 -31 16 12.134699144   14.86 14.07 13.523 13.011 CEMP-no 19 0
11 BPS CS 22892-0052 Pe* 22 17 01.6558480594 -16 39 27.051900047   14.03 13.20 13.06 12.19 KIIvw 411 0
12 HE 2323-0256 Pe* 23 26 29.8073543039 -02 39 58.037206596   15.12 14.36   13.358 CEMP-no 171 0

    Equat.    Gal    SGal    Ecl

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2020.08.07-13:14:20

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