J/A+A/704/A103 CEMP-s and CEMP-rs stars barium isotope ratio (Sitnova+, 2025)
Distinct barium isotope ratios in CEMP-s and CEMP-rs stars.
Sitnova T.M., Mashonkina L.I., Romanovskaya A.M., Giribaldi R.E., Choplin A.
<Astron. Astrophys. 704, A103 (2025)>
=2025A&A...704A.103S 2025A&A...704A.103S (SIMBAD/NED BibCode)
ADC_Keywords: Milky Way ; Stars, metal-deficient ; Abundances ;
Equivalent widths ; Optical
Keywords: nuclear reactions, nucleosynthesis, abundances - stars: abundances -
stars: atmospheres - binaries: close - stars: carbon -
stars: late-type
Abstract:
We present a spectroscopic analysis of ten carbon enhanced metal-poor
(CEMP) stars of type CEMP-s and CEMP-rs and determine their non-local
thermodynamic equilibrium (NLTE) abundances of Ba and Eu, as well as
the fractions of the odd Ba isotopes (Fodd). Determination of Fodd
in stars provides unambiguous information about the s-process
contribution to their total Ba abundance. We aim to obtain
observational constraints on the enrichment scenarios of CEMP-rs
stars. The Ba abundances inferred from the resonance BaII 4554 and
4934Å lines depend on the adopted Ba isotope mixture. We perform
calculations for different Fodd from 0.1 to 1.0 and determine the
corresponding abundances from the BaII resonance lines in each sample
star. In addition, we determine the Ba abundances from the BaII
subordinate lines, which are almost independent of F_odd. We then
compare the Ba abundances derived from the subordinate lines with
those from the BaII resonance lines. We found different F_odd values
in CEMP-s and CEMP-rs stars. CEMP-s stars exhibit
Fodd=0.05-0.03+0.07, 0.17-0.14+0.63, 0.19-0.14+0.50, and
0.19-0.12+0.33. The obtained values agree, within the error bars,
with the s-process Fodd=0.10 and the solar Fodd=0.18. Although the
uncertainties are large, in three of four stars, the possibility of Ba
isotopes origin in a pure r-process with Fodd=0.75 can be excluded.
CEMP-rs stars show Fodd=0.34-0.21+0.55, 0.36-0.14+0.23,
0.44-0.22+0.43, 0.53-0.38+0.47, and 0.57-0.31+0.43, which
are higher compared to those in CEMP-s stars. Although the
uncertainties are large, in four of five stars, the possibility of a
pure s-process origin for the Ba isotopes can be excluded. The
obtained values agree, within the error bars, with the predicted
i-process Fodd=0.6 to 0.8. Our analysis of CEMP-rs stars with
[Ba/Eu]>0 argues that their [Ba/Eu] and Fodd cannot be jointly
explained by a mixture of material produced by the r- and s-processes.
The obtained results argue that the i-process is responsible for the
chemical composition of these CEMP-rs stars.
Description:
We present a spectroscopic analysis of ten CEMP stars and determine
their Ba and Eu NLTE abundances, as well as the fractions of odd Ba
isotopes.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
stars.dat 63 10 Sample star
table2.dat 139 30 NLTE and LTE abundances and EWs (mÅ) of
BaII lines in the sample stars
table3.dat 56 23 NLTE and LTE abundances and EWs (mÅ) of
EuII lines in the sample stars
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Byte-by-byte Description of file: stars.dat
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Bytes Format Units Label Explanations
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1- 2 I2 h RAh Right ascension (J2000)
4- 5 I2 min RAm Right ascension (J2000)
7- 19 F13.10 s RAs Right ascension (J2000)
21 A1 --- DE- Declination sign (J2000)
22- 23 I2 deg DEd Declination (J2000)
25- 26 I2 arcmin DEm Declination (J2000)
28- 39 F12.9 arcsec DEs Declination (J2000)
41- 63 A23 --- Name Star name
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 23 A23 --- Name Star name
25- 28 A4 --- Param Parameter name (NLTE, LTE, EW) (G1)
30- 35 F6.2 --- Value2 ?=-99.9 BaII 4554Å, for Fodd=1.00
value for Param
37- 42 F6.2 --- Value3 ?=-99.9 BaII 4554Å, for Fodd=0.75
value for Param
44- 49 F6.2 --- Value4 ?=-99.9 BaII 4554Å, for Fodd=0.62
value for Param
51- 56 F6.2 --- Value5 ?=-99.9 BaII 4554Å, for Fodd=0.43
value for Param
58- 63 F6.2 --- Value6 ?=-99.9 BaII 4554Å, for Fodd=0.18
value for Param
65- 70 F6.2 --- Value7 ?=-99.9 BaII 4554Å, for Fodd=0.10
value for Param
72- 77 F6.2 --- Value8 BaII 4934Å, for Fodd=1.00 value for Param
79- 84 F6.2 --- Value9 BaII 4934Å, for Fodd=0.75 value for Param
86- 91 F6.2 --- Value10 BaII 4934Å, for Fodd=0.62 value for Param
93- 98 F6.2 --- Value11 BaII 4934Å, for Fodd=0.43 value for Param
100-105 F6.2 --- Value12 BaII 4934Å, for Fodd=0.18 value for Param
107-112 F6.2 --- Value13 BaII 4934Å, for Fodd=0.10 value for Param
114-119 F6.2 --- Value14 ?=-99.9 BaII 5853Å value for Param
121-126 F6.2 --- Value15 BaII 6141Å value for Param
128-133 F6.2 --- Value16 BaII 6496Å value for Param
135-139 A5 --- x_Value2 Unit of Value2-Value16 parameters
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 23 A23 --- Name Star name
25- 28 A4 --- Param Parameter name (NLTE, LTE, EW) (G1)
30- 35 F6.2 --- Value2 ?=-99.90 EuII 3819Å value for Param
37 A1 --- l_Value3 Limit flag on Value3
38- 43 F6.2 --- Value3 ?=-99.90 EuII 4129Å value for Param
45- 50 F6.2 --- Value4 ?=-99.90 EuII 4205Å value for Param
52- 56 A5 --- x_Value2 Unit of Value2-Value4 parameters
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Global notes:
Note (G1): Parameter name as follows:
NLTE = NLTE abundance
LTE = LTE abundance,
EW = equivalent width in mÅ
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Acknowledgements:
T.M. Sitnova, sitamih(at)gmail.com
(End) Patricia Vannier [CDS] 21-Nov-2025