Challenges for stellar pulsation and evolution theory

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.Comment: Invited talk presented at the JENAM 2008 Symposium No.4 "Asteroseismology and stellar evolution", eds. S. Schuh and G. Handler., Communications in Asteroseismology, 159, in press; 11 pages, 1 figur

The effects of moderately fast shellular rotation on adiabatic oscillations

We investigate adiabatic oscillations for delta Scuti star models, taking into account a moderate rotation velocity ~100 \km/s. The resulting oscillation frequencies include corrections for rotation up to second order in the rotation rate including those of near degeneracy. Effects of either a uniform rotation or a rotation profile assuming local angular momentum conservation of the form Omega=Omega(r) on oscillation frequencies are compared. As expected, important differences (around 3 microHz) are obtained in the $g$ and mixed mode regions. For higher frequency p modes, differences range between 1 microHz and 3 microHz. Such differences are likely to be detectable with future space missions such as COROT, where precisions in frequency around 0.5 microHz will be reachable.Comment: A&A, in press (18 pag, 14 fig

Constraints on parameters of B-type pulsators from combined multicolour photometry and radial velocity data. I. β\beta Cephei stars

We analyze data on pulsation amplitudes and phases for two $\beta$ Cephei stars, $\delta$ Cet and $\nu$ Eri. Str\"omgren photometry and radial velocity measurements are used simultaneously to obtain constraints on mean parameters of the stars and identification of the excited modes. The inference about the radial mode order and mean star parameters is based on comparison of certain complex parameter, $f$, determined from data, with its counterpart derived from linear nonadiabatic modelling of stellar oscillations. The theoretical $f$ values are very sensitive to the adopted opacity data. In our modelling we rely on the data from OPAL and OP projects. Significant differences were found. New seismic models of $\nu$ Eri were constructed with both the OPAL and OP opacities.Comment: 11 pages, 13 figures, A&A in pres

The role of rotation on Petersen Diagrams. II The influence of near-degeneracy

In the present work, the effect of near-degeneracy on rotational Petersen diagrams (RPD) is analysed. Seismic models are computed considering rotation effects on both equilibrium models and adiabatic oscillation frequencies (including second-order near-degeneracy effects). Contamination of coupled modes and coupling strength on the first radial modes are studied in detail. Analysis of relative intrinsic amplitudes of near-degenerate modes reveals that the identity of the fundamental radial mode and its coupled quadrupole pair are almost unaltered once near-degeneracy effects are considered. However, for the first overtone, a mixed radial/quadrupole identity is always predicted. The effect of near-degeneracy on the oscillation frequencies becomes critical for rotational velocities larger than 15-20 km/s, for which large wriggles in the evolution of the period ratios are obtained (up $10^{-2}$). Such wriggles imply uncertainties, in terms of metallicity determinations using RPD, reaching up to 0.50 dex, which can be critical for Pop. I HADS (High Amplitude \dss). In terms of mass determinations, uncertainties reaching up to 0.5 M_sun are predicted. The location of such wriggles is found to be independent of metallicity and rotational velocity, and governed mainly by the avoided-crossing phenomenon.Comment: 8 pages, 7 figures, 1 table. (accepted for publication in A&A