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

Standard spectroscopic analyses of variable stars are based on hydrostaticone-dimensional model atmospheres. This quasi-static approach has theoreticallynot been validated. We aim at investigating the validity of the quasi-staticapproximation for Cepheid variables. We focus on the spectroscopicdetermination of the effective temperature $T_\mathrm{eff}$, surface gravity$\log \,g$, microturbulent velocity $\xi_\mathrm{t}$, and a generic metalabundance $\log\,A$ -- here taken as iron. We calculate a grid of 1Dhydrostatic plane-parallel models covering the ranges in effective temperatureand gravity encountered during the evolution of a two-dimensionaltime-dependent envelope model of a Cepheid computed with theradiation-hydrodynamics code CO5BOLD. We perform 1D spectral syntheses forartificial iron lines in local thermodynamic equilibrium varying themicroturbulent velocity and abundance. We fit the resulting equivalent widthsto corresponding values obtained from our dynamical model. For thefour-parametric case, the stellar parameters are typically underestimatedexhibiting a bias in the iron abundance of $\approx-0.2\,\mbox{dex}$. To avoidbiases of this kind it is favourable to restrict the spectroscopic analysis tophotometric phases $\phi_\mathrm{ph}\approx0.3\ldots 0.65$ using additionalinformation to fix effective temperature and surface gravity. Hydrostatic 1Dmodel atmospheres can provide unbiased estimates of stellar parameters andabundances of Cepheid variables for particular phases of their pulsations. Weidentified convective inhomogeneities as the main driver behind potentialbiases. For obtaining a complete view on the effects when determining stellarparameters with 1D models, multi-dimensional Cepheid atmosphere models arenecessary for variables of longer period than investigated here.

Spectroscopic properties of a two-dimensional time-dependent Cepheid model II. Determination of stellar parameters and abundances