Tungsten in barium stars
arxiv(2024)
摘要
Classical barium stars are red giants that received from their evolved binary
companions material exposed to the slow neutron-capture
nucleosynthesis, i.e., the s-process. Such a mechanism is expected to have
taken place in the interiors of Thermally-Pulsing Asymptotic Giant Branch
(TP-AGB) stars. As post-interacting binaries, barium stars figure as powerful
tracers of the s-process nucleosynthesis, evolution of binary systems, and
mechanisms of mass transfer. The present study is the fourth in a series of
high-resolution spectroscopic analyses on a sample of 180 barium stars, for
which we report tungsten (W, Z=74) abundances. The abundances were derived
from synthetic spectrum computations of the W i absorption features at
4 843.8 Å and 5 224.7 Å. We were able to extract abundances for 94
stars; the measured [W/Fe] ratios range from ∼0.0 to 2.0 dex, increasing
with decreasing of metallicity. We noticed that in the plane [W/Fe] versus
[s/Fe] barium stars follow the same trend observed in post-AGB stars. The
observational data were also compared with predictions of the fruity and
Monash AGB nucleosynthesis models. These expect values between -0.20 and
+0.10 dex for the [W/hs] ratios, whereas a larger spread is observed in the
program stars, with [W/hs] ranging from -0.40 to +0.60 dex. The stars with
high [W/hs] ratios may represent evidence for the operation of the intermediate
neuron-capture process at metallicities close to solar.
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