We describe systematic changes in the centroid frequencies and the splitting coefficients as found using data from MDI on board SOHO, covering cycle 23. The data allow us to construct a seismic map of the evolving solar activity - covering all latitudes. At lower latitudes, the temporal evolution closely tracks that of butterfly diagram. The additional information from higher latitudes in the map is of a significant activity in the polar region, peaking at activity minimum in 1996. The most plausible source of solar oscillation frequency changes over the solar cycle is the evolution of the radial component of the small-scale magnetic field. The amplitude of the required mean field changes is ∼ 100 G at the photosphere, and increasing going inward.

The influence of a constant coronal magnetic field on solar global oscillations is investigated for a simple planar equilibrium model. The model consists of an atmosphere with a constant horizontal magnetic field on top of a unmagnetized solar interior. The focus is on the possible resonant coupling of global solar oscillation modes to local slow continuum modes of the atmosphere and the consequent damping of the global oscillations.

Through an increase in magnetic field strength, solar magnetic fields in the atmosphere or subsurface of the Sun can explain the frequency shifts observed on the time scale of the solar activity cycle. A separate study of the contribution of internal magnetic layers clarifies the relative importance of these effects. However, at the base of the convection zone, the cyclical change of orientation of magnetic field lines has a larger effect on global mode frequencies than an increase in field strength alone.

We suggest a mechanism of energy transmission from stellar radial pulsations into torsional oscillations in a dipole-like magnetic field. We show that the stellar radial pulsations cause a periodical variation of the Alfén speed which leads to the Mathieu equation for torsional Alfén waves. Harmonics with half the frequency of the pulsations have exponentially growing amplitudes. Then the energy supporting the various type of pulsations can be transformed into purely electromagnetic oscillations of the star.

From Spectroscopic observations showing that the parent stars of planetary systems are metal rich, it is suspected that this feature results from the accompanying planetary system. With the rich helioseismic data so far obtained, we determine the metal abundance distribution in the solar interior with respect to the distance from the center. This result gives constraints on the possible explanations about the metal rich feature of the stars accompanied by a planetary system.

In this work we propose a preliminary seismic investigation of δ Scuti stars in the Pleiades cluster, focusing on potential diagnostics of convection and core-overshooting. Taking into account the effect of fast rotation in the modelling, we compare observed frequencies for 4 δ Scuti stars with radial linear instability predictions. A satisfying agreement is reached between the predicted ranges of unstable modes and those derived from observations for “low-mass” stars (∼ 1.55M⊙). However, a strong disagreement is found for “high-mass” stars (∼ 1.77M⊙), whatever the mixing length (α) value. These results are compared with previous ones obtained for Praesepe.

Almost 10 years have passed since the first claims of the existence of a new class of slowly pulsating variables near the cool border of δ Scuti instability strip. The consolidated class of γ Doradus variables faces now the challenge of space. In this paper, we review the most recent theoretical and observational results of these stars and we discuss how our knowledge of their nature will benefit from data collected in the forthcoming space-borne asteroseismological missions.

We propose a pulsation driving mechanism for γ Doradus variable stars. This mechanism requires that the local convective timescale at the base of the envelope convection zone be comparable to or longer than the pulsation period. This mechanism explains both the red and blue edges of the γ Dor instability strip. We predict that some candidate γ Dor stars summarized by Handler (1999) may actually be too hot or too cool to be γ Dor variables.

Surface convection zones in γ Doradus variables (early F-type g-mode pulsators) can drive pulsation via the ‘convective driving’ mechanism. This mechanism is first proposed and studied in the context of ZZ Cetis (hydrogen-envelope white dwarfs with g-mode pulsations) by Brickhill (1991) and Goldreich & Wu (1999). We implement and develop the convective driving theory to suit the environments on γ Dors, in particular, stronger super-adiabatic gradient and weaker convective flux than those in white dwarfs. This results in a spectrum of gravity-modes being excited in the observed temperature range. However, there are more remaining problems than those that are solved.

We present a new implementation of the Riccati method for the linear stability analysis of weakly non-adiabatic g-mode pulsations in γ Doradus stars.

Hot, luminous, massive stars have strong stellar winds driven by line-scattering of the star’s continuum radiation. They are also often observed to exhibit radial or non-radial pulsations. Such pulsations are possible candidates for providing the base perturbations that induce large-scale structure in the overlying wind, and as such they could help explain various observational manifestions of wind variability, e.g., absorption enhancemens or modulations in UV P-Cygni lines of OB stars, and perhaps even moving bumps in optical emission lines of Wolf-Rayet (WR) stars. Here we review the physics of line driving, with emphasis on how perturbations induce variations in a wind outflow. In particular, we present results of a time-dependent dynamical simulation of wind variations induced by the radial pulsation of the β Cep variable BW Vulpeculae, and show that observed variability in UV wind lines can be quite well reproduced by synthetic line profiles for this model. We conclude with a discussion of recent evidence that resonances among multiple modes of non-radial pulsation in Be stars play a role in inducing mass ejections that contribute to formation of a circumstellar disk.

We numerically study the formation process of equatorial disks around isolated Be stars, using an SPH code. We find that the viscous decretion disk model naturally explains the observed disk formation episode of X Per, giving the equatorial mass-loss rate of several ×10−9 (ρ0/10−10 g cm−3) M⊙ yr−1, where ρ0 is the base density of the disk.

We present an analysis of a light curve of LBV star v532 (Romano’s star) in M33. The data consist of 881 individual photographic observations from 1960 to 2000. The star shows extremely rich periodic variations. We find that the amplitudes of the periods depend on brightness, as they rise when the star becomes brighter. We suggest that the 13.08-day period corresponds to the star’s rotation, other short periods (∼ 20 – 30 days) represent the star’s pulsations, and the longer periods are instability driven wind pulsations. The spectral variability of v532 is also strong, with the spectrum excitation depending on the stellar brightness.

In the last decades considerable progress has been achieved in the physical understanding and modelling of dusty stellar atmospheres and surroundings, as represented by stationary dust driven winds, pulsating shells of Miras and LPVs, episodic phenomena, like occultations of RCrB stars, the atmospheres of brown dwarfs, or even by “hot” objects like dust forming Wolf-Rayet stars.

For all these systems the notions “understanding” and “modelling” depend on the level of the physical approach defined by specific perspectives chosen by a basic “window of perception” for each class of particular objects and its appropriate description within this frame. This is defined by the fundamental assumptions with regard to the global and local appearance and the properties of the considered object, its focused characteristic length and time scales of the various determining processes taken into account, and, of course, by an appropriate body of physical equations necessary for an adequate description within the context of the adopted perspective. In this view, any real approach concentrates on special aspects (or a combination of it), like radiative transfer, wind generation, spectral appearance, dynamical behaviour, global and local stability, cluster nucleation, grain growth and processing, chemistry, interplay of physical and chemical processes, etc. Consequently, any approach projects only particular properties of the considered object, each constituting important ingredients necessary for a final consistent quantitative modelling and a comprehensive physical understanding.

We present a new generation of dynamic model atmospheres for pulsating AGB stars based on a combined solution of hydrodynamics, frequency-dependent radiative transfer, and time-dependent dust formation. At present, we are performing a systematic study of the dependence of atmospheric structure, observable properties and mass loss on stellar parameters and pulsation properties. Preliminary results show a good agreement with observations and a considerable improvement compared to existing grey dynamical models.

We present time series of observed and synthetic ISO-SWS spectra of oxygen-rich Mira variables covering the wavelength range between 2.36 and 7.75 μm. The calculations are based on new dynamical models, which have been computed with a non-grey radiative transfer taking into account all relevant molecular opacities. It turns out that many features in the ISO spectra of cool long period variables which could not be reproduced within the framework of classical hydrostatic model atmospheres nor with grey dynamical calculations can now be understood without any additional assumptions. This is especially true for the water bands, which dominate the opacity in the infrared range of M-type Miras.

We are currently studying carbon based dust types of relevance for carbon-rich AGB stars, to obtain a better understanding of the influence of the optical and chemical properties of the grains on the mass loss of the star. An investigation of the complex interplay between hydrodynamics, radiative transfer and chemistry has to be based on a better knowledge of the micro-physics of the relevant dust species.

The formation of dust and wind in luminous AGB-stars has been studied so far mainly for solar metallicities. Here, the impact of the dust component on the driving mechanism of the massive outflows and the non-linear coupling to hydro/-thermodynamics leads to the creation of dust-induced shock waves, the occurrence of onion-like spatial dust distributions around the star, time-dependent dust-size distributions, multi-periodicity, and the onset of a super-wind phase (see Sedlmayr, these proceedings). The question remains whether these phenomena appear also in metal-deficient models of AGB-stars like those in the Large Magellanic Cloud (LMC).

I give a brief review and interpretation of the evolution, mass loss and pulsation of AGB stars in the Large Magellanic Cloud.

We discuss velocity variations in different layers of an AGB star’s atmosphere. Periodic and nonperiodic changes are observed. From a large sample of data we derive mean velocity curves for miras and semiregular variables.