English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

We have computed a grid of hydrostatic spherical COMARCS models for C starscovering 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 oxygenand nitrogen is increased relative to a scaled solar element mixture. Suchabundance 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 theatmospheric structures we have calculated synthetic spectra and photometry forall of the models in a consistent way.  The sequences with changed [O/Z] and [N/Z] can be used to derive correctionterms, which are applied to the colours predicted for a certain combination ofeffective temperature, surface gravity, metallicity and carbon excess. If oneneglects these shifts in case of a variable oxygen amount, taking [C-O] insteadof C/O gives much better results, since the first quantity dominates theformation of many important molecular species. For the warmer C giants withweaker 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 transfercalculations for the models and observable properties are treated consistently.The corresponding changes due to the abundances often become significantlylarger than the deviations caused by uncertainties of the stellar parameters orby a optically thin dust shell. Photometric data and low or medium resolutionspectra are not sufficient to derive the mentioned quantities.

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