Carbon stars with increased oxygen and nitrogen abundances: hydrostatic dust-free model atmospheres - INSU - Institut national des sciences de l'Univers Access content directly
Journal Articles Monthly Notices of the Royal Astronomical Society Year : 2019

Carbon stars with increased oxygen and nitrogen abundances: hydrostatic dust-free model atmospheres

B. Aringer
  • Function : Author
P. Marigo
  • Function : Author
W. Nowotny
  • Function : Author
L. Girardi
  • Function : Author
M. Mečina
  • Function : Author

Abstract

We have computed a grid of hydrostatic spherical COMARCS models for C stars covering metallicities from [Z/H] = 0 to -2 and values of the carbon excess [C-O] from 6.41 to 9.15, plus some temperature sequences, where the amount of oxygen and nitrogen is increased relative to a scaled solar element mixture. Such abundance variations may appear during the late stages of stellar evolution. Our study covers changes of [O/Z] and [N/Z] going up to +0.5. Based on the atmospheric structures we have calculated synthetic spectra and photometry for all of the models in a consistent way. The sequences with changed [O/Z] and [N/Z] can be used to derive correction terms, which are applied to the colours predicted for a certain combination of effective temperature, surface gravity, metallicity, and carbon excess. If one neglects these shifts in case of a variable oxygen amount, taking [C-O] instead of C/O gives much better results, since the first quantity dominates the formation of many important molecular species. For the warmer C giants with weaker pulsation it is in principle possible to determine [C-O], [O/Z], or [N/Z] from high-resolution spectra, when the opacities in the radiative transfer calculations for the models and observable properties are treated consistently. The corresponding changes due to the abundances often become significantly larger than the deviations caused by uncertainties of the stellar parameters or by an optically thin dust shell. Photometric data and low- or medium-resolution spectra are not sufficient to derive the mentioned quantities.
Fichier principal
Vignette du fichier
stz1429.pdf (1.46 Mo) Télécharger le fichier
Origin : Publisher files allowed on an open archive

Dates and versions

insu-03666731 , version 1 (26-06-2023)

Identifiers

Cite

B. Aringer, P. Marigo, W. Nowotny, L. Girardi, M. Mečina, et al.. Carbon stars with increased oxygen and nitrogen abundances: hydrostatic dust-free model atmospheres. Monthly Notices of the Royal Astronomical Society, 2019, 487, pp.2133-2147. ⟨10.1093/mnras/stz1429⟩. ⟨insu-03666731⟩
7 View
1 Download

Altmetric

Share

Gmail Facebook X LinkedIn More