J/A+A/581/A22 67 CEMP-s stars model analysis (Abate+, 2015)
Carbon-enhanced metal-poor stars: a window on AGB nucleosynthesis and binary
evolution. II. Statistical analysis of a sample of 67 CEMP-s stars.
Abate C., Pols O.R., Izzard R.G., Karakas A.I.
<Astron. Astrophys., 581, A22-22 (2015)>
=2015A&A...581A..22A 2015A&A...581A..22A (SIMBAD/NED BibCode)
ADC_Keywords: Stars, double and multiple ; Stars, metal-deficient ;
Stars, masses
Keywords: stars: abundances - stars: AGB and post-AGB - binaries: general -
stars: chemically peculiar - stars: Population II - Galaxy: halo
Abstract:
Many of the carbon-enhanced metal-poor (CEMP) stars that we observe in
the Galactic halo are found in binary systems and show enhanced
abundances of elements produced by the slow neutron-capture process
(s-elements). The origin of the peculiar chemical abundances of these
CEMP-s stars is believed to be accretion in the past of enriched
material from a primary star in the asymptotic giant branch (AGB)
phase of its evolution. We investigate the mechanism of mass transfer
and the process of nucleosynthesis in low-metallicity AGB stars by
modelling the binary systems in which the observed CEMP-s stars were
formed. For this purpose we compare a sample of 67 CEMP-s stars with a
grid of binary stars generated by our binary evolution and
nucleosynthesis model. We classify our sample CEMP-s stars in three
groups based on the observed abundance of europium. In CEMP-s/r stars
the europium-to-iron ratio is more than ten times higher than in the
Sun, whereas it is lower than this threshold in CEMP-s/nr stars. No
measurement of europium is currently available for CEMP-s/ur stars. On
average our models reproduce the abundances observed in CEMP-s/nr
stars well, whereas in CEMP-s/r stars and CEMP-s/ur stars the
abundances of the light-s elements (strontium, yttrium, zirconium) are
systematically overpredicted by our models, and in CEMP-s/r stars the
abundances of the heavy-s elements (barium, lanthanum) are
underestimated. In all stars our modelled abundances of sodium
overestimate the observations. This discrepancy is reduced only in
models that underestimate the abundances of most of the s-elements.
Furthermore, the abundance of lead is underpredicted in most of our
model stars, independent of the metallicity. These results point to
the limitations of our AGB nucleosynthesis model, particularly in the
predictions of the element-to-element ratios. In our models CEMP-s
stars are typically formed in wide systems with periods above
10000-days, while most of the observed CEMP-s stars are found in
relatively close orbits with periods below 5000-days. This evidence
suggests that either the sample of CEMP-s binary stars with known
orbital parameters is biased towards short periods or that our wind
mass-transfer model requires more efficient accretion in close orbits.
Description:
Our database of observed very metal-poor stars is based on 580 stars
catalogued in the SAGA observational database (Suda et al.
2008PASJ...60.1159S 2008PASJ...60.1159S; 2011, Cat. J/MNRAS/412/843, last updated in
January 2015) with iron abundance -2.8≤[Fe/H]≤-1.8. Among these
objects we select the stars with observed abundances of carbon and
barium and we ignore stars with only upper or lower limits. In some
stars measurements of element abundances or stellar parameters are
available from multiple sources.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 60 67 Surface gravities, temperatures and chemical
properties observed in the 67 CEMP-s stars of
our sample
table2.dat 77 43 Physical parameters of the model CEMP-s stars
with nu≥2 computed with model set A with WRLOF
wind-accretion efficiency and spherically
symmetric wind
table3.dat 77 43 Physical parameters of the model CEMP-s stars
with nu≥2 computed with model set B with WRLOF
wind-accretion efficiency and spherically
symmetric wind
table4.dat 77 43 Physical parameters of the model CEMP-s stars
with nu≥2 computed with model set C with WRLOF
wind-accretion efficiency and spherically
symmetric wind
table5.dat 77 24 Physical parameters of the model CEMP-s stars
with nu≤1 computed with model set A
table6.dat 77 24 Physical parameters of the model CEMP-s stars
with nu≤1 computed with model set B
table7.dat 77 24 Physical parameters of the model CEMP-s stars
with nu≤1 computed with model set C
table8.dat 87 40 Confidence ranges of the input parameters of the
modelled CEMP-s stars with chi2/nu≤3 and
nu≥2 computed with model set A with WRLOF
wind-accretion efficiency and spherically
symmetric wind
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See also:
J/A+A/574/A129 : The First CEMP star in the Sculptor dSph (Skuladottir+, 2015)
J/A+A/579/A28 : Abundances of 3 CEMP stars (Bonifacio+, 2015)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 2 A2 --- Sample Sample (G1)
4- 17 A14 --- Name Star name
19- 21 F3.1 [cm/s2] logg Surface gravity
23- 26 F4.2 [cm/s2] e_logg rms uncertainty on logg
28- 31 I4 K Teff Effective temperature
32 A1 --- l_Porb Limit flag on Prob
33- 40 F8.3 d Porb ? Orbital period
42- 43 I2 --- N Number of observed elements
45- 48 F4.1 [-] [Fe/H] Metallicity
50- 52 F3.1 [-] [C/Fe] Abundance [C/Fe]
54- 56 F3.1 [-] [s/Fe] Abundance [s/Fe] (1)
58- 60 F3.1 [-] [Eu/Fe] ? Abundance [s/Fe]
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Note (1): Barium abundance is used as indicator of s-elements. In HD 198269,
HD 13826 and HD 201626 lanthanum is used because barium is not observed.
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Byte-by-byte Description of file: table[234567].dat
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Bytes Format Units Label Explanations
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1- 2 A2 --- Sample Sample (G1)
4- 17 A14 --- Name Star name
19- 21 F3.1 Msun M1i Primary mass fitted parameter, M1,i
23- 29 E7.3 d MPMZ Mass of the PMZ fitted parameter, MPMZ
31- 34 F4.2 Msun M2i Secondary mass fitted parameter, M2,i
36- 42 E7.3 d Pi Orbital period fitted parameter
44- 47 F4.2 Msun DMacc Mass accreted by the secondary star,
ΔMacc
49- 55 E7.3 d Pf Orbital period of the binary when the secondary
star best reproduces the observed logg and
surface abundances
57- 63 E7.3 d PfI ? Final period determined in paper I
(Abate et al., 2015A&A...576A.118A 2015A&A...576A.118A)
(except in tables a4 and a7)
65- 69 F5.1 --- chi2min Minimum chi2
71- 72 I2 --- nu Number of degrees of freedom of the fit
74- 77 F4.1 --- chi2/nu ? Reduced chi2R of the best fit
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Byte-by-byte Description of file: table8.dat
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Bytes Format Units Label Explanations
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1- 2 A2 --- Type Type (G1)
4- 15 A12 --- Name Star name
18- 21 F4.2 Msun M1ib ? Best Primary mass fitted parameter
23- 26 F4.2 Msun M1im ?=- Minimum primary mass fitted parameter
28- 31 F4.2 Msun M1iM ?=- Maximum primary mass fitted parameter
33- 36 F4.2 10-3 MPMZb ?=- Best mass of the PMZ fitted parameter
38- 41 F4.2 10-3 MPMZm ?=- Minimum mass of the PMZ fitted parameter
43- 46 F4.2 10-3 MPMZM ?=- Maximum mass of the PMZ fitted parameter
48- 51 F4.2 Msun M2ib ?=- Best secondary mass fitted parameter
53- 56 F4.2 Msun M2im ?=- Minimum secondary mass fitted parameter
58- 61 F4.2 Msun M2iM ?=- Maximum secondary mass fitted parameter
63- 69 E7.3 d Pib ?=- Best orbital period fitted parameter
72- 78 E7.3 d Pim ? Minimum orbital period fitted parameter
81- 87 E7.3 d PiM ? Maximum orbital period fitted parameter
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Global notes:
Note (G1): Sample as follows:
nr = CEMP-s/nr stars
r = CEMP-s/r stars
ur = CEMP-s/ur stars
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History:
From electronic version of the journal
References:
Abate et al., Paper I 2015A&A...576A.118A 2015A&A...576A.118A
(End) Patricia Vannier [CDS] 04-Nov-2015