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Register a new userThe Role of Opacities in Stellar Pulsation
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We examine the role of opacities in stellar pulsation with reference to Cepheids and RR Lyraes, and examine the effect of augmented opacities on the theoretical pulsation light curves in key temperature ranges. The temperature ranges are provided by recent experimental and theoretical work that have suggested that the iron opacities have been considerably underestimated. For Cepheids, we find that the augmented opacities have noticeable effects in certain period ranges (around $log P approx 1$) even though there is a degeneracy with mixing length. We also find significant effects in theoretical models of B-star pulsators.
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We present what constraints on opacities can be derived from the analysis of stellar pulsations of BA-type main-sequence stars. This analysis consists of the construction of complex seismic models which reproduce the observed frequencies as well as the bolometric flux amplitude extracted from the multi-colour photometric variations. Stellar seismology, i.e., {it asteroseismology}, is a relatively young branch of astrophysics and, currently, provides the most accurate test of the theory of internal structure and evolution. We show that opacities under stellar conditions need to be modified at the depth of temperatures $T=110~000-290~000$,K. The revision of opacity data is of great importance because they are crucial for all branches of astrophysics.
The ANTARES code has been designed for simulation of astrophysical flows in a variety of situations, in particular in the context of stellar physics. Here, we describe extensions as necessary to model the interaction of pulsation and convection in classical pulsating stars. These extensions encomprise the introduction of a spherical grid, movable in the radial direction, specific forms of grid-refinement and considerations regarding radiative transfer. We then present the basic parameters of the cepheid we study more closely. For that star we provide a short discussion of patterns of the H+HeI and the HeII convection zones and the interaction with pulsation seen in the pdV work or atmospheric structures.
During the last few decades, great effort has been made towards understanding hydrodynamical processes which determine the structure and evolution of stars. Up to now, the most stringent constraints have been provided by helioseismology and stellar cluster studies. However, the contribution of asteroseismology becomes more and more important, giving us an opportunity to probe the interiors and atmospheres of very different stellar objects. A variety of pulsating variables allows us to test various parameters of micro- and macrophysics by means of oscillation data. I will review the most outstanding key problems, both observational and theoretical, of which our knowledge can be improved by means of asteroseismology.
New infrared spectra of 33 Galactic carbon stars from FORCAST on SOFIA reveal strong connections between stellar pulsations and the dust and molecular chemistry in their circumstellar shells. A sharp boundary in overall dust content, which predominantly measures the amount of amorphous carbon, separates the semi-regular and Mira variables, with the semi-regulars showing little dust in their spectra and the Miras showing more. In semi-regulars, the contribution from SiC dust increases rapidly as the overall dust content grows, but in Miras, the SiC dust feature grows weaker as more dust is added. A similar dichotomy is found with the absorption band from CS at $sim$7.3 $mu$m, which is generally limited to semi-regular variables. Observationally, these differences make it straightforward to distinguish semi-regular and Mira variables spectroscopically without the need for long-term photometric observations or knowledge of their distances. The rapid onset of strong SiC emission in Galactic carbon stars in semi-regulars variables points to a different dust-condensation process before strong pulsations take over. The break in the production of amorphous carbon between semi-regulars and Miras seen in the Galactic sample is also evident in Magellanic carbon stars, linking strong pulsations in carbon stars to the strong mass-loss rates which will end their lives as stars across a wide range of metallicities.
We present a comprehensive seismic study of the three pulsating stars of $beta$ Cep/SPB type: $ u$ Eridani, 12 Lacertae and $gamma$ Pegasi. Models with the modified mean opacity profile are constructed in order to account for both the observed frequency range and the values of some individual frequencies. To decrease the number of possible solutions, we make use of the non-adiabatic parameter $f$, whose value is very sensitive to subphotospheric layers where pulsations are driven. This complex seismic modelling show the need for a significant modification of the opacity profile.
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