2009A&A...508.1359I


C.D.S. - SIMBAD4 rel 1.7 - 2021.03.01CET08:08:55

2009A&A...508.1359I - Astronomy and Astrophysics, volume 508, 1359-1374 (2009/12-4)

Population synthesis of binary carbon-enhanced metal-poor stars.

IZZARD R.G., GLEBBEEK E., STANCLIFFE R.J. and POLS O.R.

Abstract (from CDS):

The carbon-enhanced metal-poor (CEMP) stars constitute approximately one fifth of the metal-poor ([Fe/H]≲-2) population but their origin is not well understood. The most widely accepted formation scenario, at least for the majority of CEMP stars which are also enriched in s-process elements, invokes mass-transfer of carbon-rich material from a thermally-pulsing asymptotic giant branch (TPAGB) primary star to a less massive main-sequence companion which is seen today. Recent studies explore the possibility that an initial mass function biased toward intermediate-mass stars is required to reproduce the observed CEMP fraction in stars with metallicity [Fe/H]←2.5. These models also implicitly predict a large number of nitrogen-enhanced metal-poor (NEMP) stars which is not seen. In this paper we investigate whether the observed CEMP and NEMP to extremely metal-poor (EMP) ratios can be explained ewithout invoking a change in the initial mass function. We construct binary-star populations in an attempt to reproduce the observed number and chemical abundance patterns of CEMP stars at a metallicity [Fe/H]~-2.3. Our binary-population models include synthetic nucleosynthesis in TPAGB stars and account for mass transfer and other forms of binary interaction. This approach allows us to explore uncertainties in the CEMP-star formation scenario by parameterization of uncertain input physics. In particular, we consider the uncertainty in the physics of third dredge up in the TPAGB primary, binary mass transfer and mixing in the secondary star. We confirm earlier findings that with current detailed TPAGB models, in which third dredge up is limited to stars more massive than about 1.25M, the large observed CEMP fraction cannot be accounted for. We find that efficient third dredge up in low-mass (less than 1.25M), low-metallicity stars may offer at least a partial explanation for the large observed CEMP fraction while remaining consistent with the small observed NEMP fraction.

Abstract Copyright:

Journal keyword(s): stars: carbon - binaries: close - stars: chemically peculiar - Galaxy: halo - Galaxy: stellar content - nuclear reactions, nucleosynthesis, abundances

CDS comments: Paragraph.3 HE 0400-2040 is a probable misprint for HE 0400-2030.

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 - 2021
#notes
1 HD 224959 Pe* 00 02 08.0224361239 -02 49 12.239963584   10.6 9.55     C1,1_CH4 88 0
2 PN BoBn 1 PN 00 37 16.03 -13 42 58.6   16       ~ 126 1
3 NAME SMC G 00 52 38.0 -72 48 01   2.79 2.2     ~ 9698 1
4 HD 5223 Pe* 00 54 13.6094686085 +24 04 01.522268338   9.88 8.47     C-H2IIIb: 114 0
5 CD-26 304 Pe* 00 57 18.1376089543 -25 26 09.699477820   13.57 12.69 12.198 11.759 CEMP-s 63 1
6 NAME Magellanic Clouds GrG 03 00 -71.0           ~ 5857 1
7 HE 0400-2030 Pe* 04 02 14.8023718086 -20 21 53.528503085   14.921 14.033 13.605 13.164 CEMP-s 18 0
8 HE 1305+0132 Pe* 13 08 17.7580021762 +01 16 49.476922375   14.15 12.57 11.910 11.443 CEMP-s 25 0
9 LP 625-44 Pe* 16 43 14.0364804654 -01 55 30.408914037   12.84 11.68     CEMP-s 102 0
10 BPS CS 30322-0023 * 21 30 32.1818570433 -46 16 24.615679322   13.473 12.166 11.498 10.908 ~ 48 0
11 HE 2134-3940 Pe* 21 37 45.7673672486 -39 27 22.314122762   13.790 12.660 12.160 11.760 KIIvw 82 0
12 BPS CS 22956-0028 SB* 21 44 48.7079276715 -63 22 09.738970394   13.317 13.0     CEMP-s 23 0

    Equat.    Gal    SGal    Ecl

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