Hydrodynamics and multi-level non-LTE radiative transfer in pulsating atmospheres: Cepheids

Details Hydrodynamics and multi-level non-LTE radiative transfer in pulsating atmospheres: Cepheids Hydrodynamics and multi-level non-LTE radiative transfer in pulsating atmospheres: Cepheids

Dec 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993ap%26ss.210..329s&link_type=abstract

Astrophysics and Space Science (ISSN 0004-640X), vol. 210, no. 1-2, p. 329-330 (IAU Colloquium 134)

Astronomy and Astrophysics

Astrophysics

2

Cepheid Variables, Hydrodynamics, Local Thermodynamic Equilibrium, Radiative Transfer, Stellar Atmospheres, Stellar Oscillations, Stellar Spectra, Atmospheric Models, Spectrum Analysis, Stellar Models, Time Dependence

Scientific paper

The atmospheres of classical Cepheids cannot be represented adequately by a sequence of hydrostatic equilibrium atmospheric models. Observational evidence for shocks is also available at least since Kraft (1956). Both the disequilibrium and the non-linear phenomena affect the emergent spectra and spectral line profiles of the Cepheids. In the lower amplitude variables the effects may be subtle, yet still lead to significant systematic discrepancies. We have developed the code HERMES for time-dependent treatment of hydrodynamics and non-local thermodynamic equilibrium (non-LTE) radiative transfer in the atmospheres of classical Cepheids with periods shorter than 12 days. Our approach is applicable to stars in which the formed shock waves do not dominate the energy balance of the atmosphere. We present time-dependent models of Cepheid atmospheres, built in a semi-empirical way and with forms of the driving piston of the pulsation taken from interior envelope computations. At present we have studied the ways in which the non-linear phenomena in a pulsating atmosphere affect different spectral lines, and the effect on measured observables (e.g., velocities, temperatures, etc.).

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