Аннотация
The precise determination of carbon abundances, together with N and O, is a
key ingredient to understanding different phases of stellar evolution. We aim
at enabling a reliable carbon spectroscopy for our unified NLTE atmosphere code
FASTWIND. We develop a new carbon model atom including CII/III/IV/V, and
discuss specific problems related to carbon spectroscopy in O-type stars. By
comparing with high-resolution spectra from six O-type stars, we check in how
far observational constraints can be reproduced by our new carbon line
synthesis. Carbon lines are even more sensitive to a variation of effective
temperature, gravity, and mass loss rate, than hydrogen/helium lines. We are
able to reproduce most of the observed lines from our stellar sample, and to
estimate those specific carbon abundances which bring the lines from different
ions into agreement. For hot dwarfs and supergiants earlier than O7, X-rays
from wind-embedded shocks can have an impact on the synthesized line strengths,
particularly for CIV, potentially affecting the abundance determination.
Dielectronic recombination has a significant impact on the ionization balance
in the wind. We have demonstrated our capability to derive realistic carbon
abundances by means of FASTWIND, using our recently developed model atom. We
found that complex effects can have a strong influence on the carbon ionization
balance in hot stars. For a further understanding, the UV range needs to be
explored as well. By means of detailed nitrogen and oxygen model atoms
available to use, we will be able to perform a complete CNO abundance analysis
for larger samples of massive stars, and to provide constraints on
corresponding evolutionary models and aspects.
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