Magnesium isotopes and s-process elements in the barium star HR 774
We have analyzed low-noise high-resolution Reticon spectra of MgH and selected unblended s-process element lines in the Ba star HR 774. We find that the isotopic abundances of Mg are terrestrial (/sup 24/Mg:/sup 25/Mg:/sup 26/Mg=79:10:11). Large overabundances of the s-process elements (Y, +0.9 dex; Zr, +0.8 dex; Mo, +1.0 dex; La, +1.1 dex; Nd, +1.5 dex) with respect to the normal K giant ..beta.. Gem are determined.These results imply that the neutrons responsible for the s-process enhancements are provided by the /sup 13/C(..cap alpha..,n)/sup 16/O reaction and not the /sup 22/Ne(..cap alpha..,n)/sup 25/ Mg reaction. If the latter reaction were the primary neutron source, substantial overabundances of /sup 25/Mg and /sup 26/Mg would be predicted for HR 774, e.g., /sup 24/Mgapprox. =/sup 25/Mgapprox. =/sup 26/Mg. This is incompatible with our analysis of the MgH lines. Our conclusion accords with the theoretical expectations of Truran and Iben who suggest that in low-mass Ba stars, such as HR 774, /sup 13/C(..cap alpha..,n)/sup 16/O rather than /sup 22/Ne(..cap alpha..,n)/sup 25/Mg is the major source of neutrons.Iron is found to be 0.2 dex deficient with respect to ..beta.. Gem. Carbon, nitrogen, and oxygen abundances are determined by analysis of Reticon spectra of Swan system C/sub 2/ lines, red system CN lines, and the 6300 A forbidden O I line. Nitrogen and oxygen have the same abundances as in a 0.2 dex metal-deficient, and otherwise normal, mixed K giant, while carbon is 0.4 dex overabundant. The /sup 12/C//sup 13/C ratio is 23 +- 2. In addition, /sup 12/C//sup 13/C ratios of 23 +- 3, 13 +- 1, and 24 +- 2 have been determined for the Ba stars HR 2392, HR 4474,and HR 5058, respectively. These results are used to interpret the evolutionary state of the Ba stars.
- Research Organization:
- McDonald Observatory and Department of Astronomy, University of Texas at Austin
- OSTI ID:
- 6465174
- Journal Information:
- Astrophys. J.; (United States), Vol. 227:1
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
GENERAL PHYSICS
MAGNESIUM ISOTOPES
ISOTOPE RATIO
S PROCESS
RED GIANT STARS
ABUNDANCE
CHEMICAL COMPOSITION
ENERGY SPECTRA
EXPERIMENTAL DATA
ISOLATED VALUES
NEUTRONS
NUCLEAR REACTIONS
NUCLEOSYNTHESIS
STAR MODELS
STELLAR ATMOSPHERES
ALKALINE EARTH ISOTOPES
ATMOSPHERES
BARYONS
DATA
DATA FORMS
ELEMENTARY PARTICLES
FERMIONS
GIANT STARS
HADRONS
INFORMATION
ISOTOPES
MATHEMATICAL MODELS
NUCLEONS
NUMERICAL DATA
SPECTRA
STAR EVOLUTION
STARS
640102* - Astrophysics & Cosmology- Stars & Quasi-Stellar
Radio & X-Ray Sources