Abstract:
A comprehensive abundance analysis providing rare insight into the chemical history of lead
stars is still lacking. We present results from high-resolution (R ∼ 50 000) spectral analyses of
three CH stars, HD 26, HD 198269 and HD 224959, and, a carbon star with a dusty envelope,
HD 100764. Previous studies on these objects are limited by both resolution and wavelength
regions and the results differ significantly from each other. We have undertaken to reanalyse the
chemical composition of these objects based on high-resolution Subaru spectra covering the
wavelength regions 4020–6775 Å. Considering local thermodynamic equilibrium and using
model atmospheres, we have derived the stellar parameters, the effective temperatures Teff,
surface gravities log g, and metallicities [Fe/H] for these objects. The derived parameters
for HD 26, HD 100764, HD 198269 and HD 224959 are (5000, 1.6, −1.13), (4750, 2.0
−0.86), (4500, 1.5, −2.06) and (5050, 2.1, −2.44), respectively. The stars are found to exhibit
large enhancements of heavy elements relative to iron in conformity to previous studies.
Large enhancement of Pb with respect to iron is also confirmed. Updates on the elemental
abundances for several s-process elements (Y, Zr, La, Ce, Nd, Sm and Pb) along with the
first-time estimates of abundances for a number of other heavy elements (Sr, Ba, Pr, Eu, Er
and W) are reported. Our analysis suggests that neutron-capture elements in HD 26 primarily
originate in the s-process while the major contributions to the abundances of neutron-capture
elements in the more metal-poor objects HD 224959 and HD 198269 are from the r-process,
possibly from materials that are pre-enriched with products of the r-process.
