Computer Science – Numerical Analysis
Scientific paper
Nov 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994a%26a...291..209f&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 291, no. 1, p. 209-225
Computer Science
Numerical Analysis
18
Nonlinearity, Numerical Analysis, Radiative Transfer, Stellar Atmospheres, Stellar Models, Stellar Oscillations, Variable Stars, Eddington Approximation, Opacity, Pressure Gradients, Radial Velocity
Scientific paper
We employ an implicit adaptive grid technique to investigate radiative full amplitude models of RR-Lyrae stars. To give an insight into the adoptive method we present a sequence of pulsating envelopes corresponding to a horizontal path through the instability strip. The stellar mass, luminosity and chemical composition are fixed at 0.578 solar mass, 64.3 solar luminosity and (X,Y,Z) = (0.7,0.299,0.001) respectively and the effective temperature is varied from 6000 to 7100 K. Simultaneously with the nonlinear pulsating envelope we are able to model the stellar atmosphere as demonstrated for one particular set of stellar parameters. Recent tables from the opacity project (Seaton et al. 1994) are used for the opacity and the equation of state is taken from Wuchterl (1990). Time-dependent grey radiative transfer is included by solving the moment equations of the transfer equation and we use a variable Eddington factor to close the moment system. Employing an adaptive grid algorithm the numerical scheme is second order in time and space (time centered and monotonic second order advection), and an artificial tensor viscosity is implemented to handle shock waves. In this article we demonstrate that our adaptive numerical method is an efficient state of the art approach to nonlinear radial stellar pulsations. The adaptive grid can be tailored to resolve the driving regions of the star and track them continuously throughout the whole pulsation cycle. As a consequence we are able to calculate accurate light- and radial velocity curves with shapes comparable to observations and without numerical perturbations. The model including the stellar atmosphere exhibits periodical variations of the atmospheric structure accompanied by strong shock waves leading to velocity amplitudes of about 170 km/s at the outer boundary of the model.
Dorfi Ernst A.
Feuchtinger Michael U.
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