Astronomy and Astrophysics – Astronomy
Scientific paper
Oct 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998aj....116.1977p&link_type=abstract
The Astronomical Journal, Volume 116, Issue 4, pp. 1977-1983.
Astronomy and Astrophysics
Astronomy
19
Stars: Abundances, Stars: Chemically Peculiar
Scientific paper
We report on the analysis of high-resolution optical spectra of the yellow component of the symbiotic star He2-467. The chemical composition of its atmosphere reveals He2-467 to be a metal-poor K giant with [Fe/H] = -1.1. From a set of 14 Fe i lines, its radial velocity is found to be -106.9 +/- 0.5 km s^-1. This high velocity plus low metallicity points to He2-467 being a halo star. The K giant in He2-467 is also enriched in the heavy s-process elements. Because its luminosity is below that for an asymptotic giant branch (AGB) star that could have commenced shell helium-burning (via thermal pulses) and become self-enriched in the neutron-capture elements, we ascribe its heavy-element excess to the barium star phenomenon. In this scenario, the secondary component accreted matter from the primary (now the white dwarf) when it was a thermally pulsing AGB star overabundant in s-process elements. The heavy-element abundance distribution of He2-467, as well as its atmospheric parameters, is almost identical to two yellow symbiotics analyzed previously, AG Dra and BD -21 deg3873. In particular, its neutron exposure parameter, tau, which characterizes the s-process abundance distribution, is larger than for solar metallicities (with a single-exposure tau = 1.1 millibarn^-1). Also, analysis of the rubidium abundance in He2-467 reveals that the s-process ratio of N(Rb)/N(Zr) is much larger than for solar metallicity s-process material, indicating that the s-process neutron density is considerably larger at lower metallicities, in agreement with the ^13C(alpha, n)^16O neutron source.
Cunha Katia
Pereira Claudio Bastos
Smith Verne V.
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