When compared with observation, stellar pulsation model predictions provide a test of stellar envelope opacities. Of specific interest, is the radially pulsating extreme helium star V652 Her for which luminosity and radial velocity observations are published. Nonlinear pulsation models of V652 Her, calculated using Opacity Project (OP) opacities, predict luminosity and radial velocity variations in close agreement with observation.

For asteroseismological reasons the discovery of new pulsating degenerate stars is important. Bradley (1993) lists the number of known pulsating white dwarfs at that time - 23 known DAV (ZZ Ceti) stars, 7 known DBV stars and 5 known DOV (PG1159) stars. Of these degenerate pulsators 80% (including all DBVs) are in the northern hemisphere. This illustrates the great incompleteness in the search for such objects in the southern hemisphere.

The Edinburgh-Cape Blue Object Survey is a potential source of candidate degenerate pulsators in the southern hemisphere (Stobie et al. 1992). The blue stellar objects are identified from COSMOS scans of U and B plates taken with the UK Schmidt Telescope. Follow-up photometry and spectroscopy are being obtained at the South African Astronomical Observatory (SAAO) to classify and determine the nature of each blue stellar object. Currently, over 190 DA white dwarfs have been identified, of which the majority are not in existing catalogues (O’Donoghue et al. 1993). From these white dwarfs, we have selected DA stars with B-V colours near or within the range 0.15 ≤ B-V ≤ 0.25 together with all the non-DA degenerate stars (DO, DB, etc.) to monitor for variability.

We show that the proper motion of a pulsating star results in a secular increase of the radial velocity of the star and consequently contributes to the observed . We found that this mechanism is very important in studying period changes in pulsating DA white dwarfs, where its effect is comparable with the expected evolutionary period change in these stars due to their cooling.

Previous studies of the southern DAV white dwarf L19-2 have revealed that it pulsates non-radially in at least five modes with periods ~ 102 s and amplitudes less than 10 mmag. All of these modes showed fine structure splitting, but the one-day aliases resulting from the gaps in the single-site data made identification of the various frequencies, at best, difficult. Recent observations of L19-2 obtained from Mt. John (NZ) are presented, along with a discussion of the prospects for a Whole Earth Telescope run on this object scheduled for 1995.

IC 418 belongs to the group of about a dozen planetary nebulae with central stars that show irregular spectroscopic and photometric variations. Recent theoretical results provide arguments that this group may constitute a new class of pulsators. We present new photometric observations of the nucleus of IC 418 showing variations with a timescale of about 1/4 day. We discuss two possible explanations of the observed phenomena: pulsational instability and an unstable wind.

Neutron stars display phenomena which result from the burning of accreted nuclear fuel in their surface layers. In addition to producing X-ray bursts and other temporal phenomema, such burning can excite oscillation modes of the neutron star. Here we investigate the stability of R-modes in uniformly rotating neutron stars using nonadiabatic pulsation calculations of steady burning envelopes on accreting neutron stars. We find that the fundamental R-modes are unstable for a large range of accretion rates, and thus might manifest themselves observationally in the power spectra of accreting sources above about 1 kHz.

Following the report of solar-like oscillations in the G0 V star η Boo (Kjeldsen et al. 1995), a first attempt to model the observed frequencies was made by Christensen-Dalsgaard et al. (1995). This attempt succeeded in reproducing the observed frequency separations Δv and δv02, although there remained a difference of ∼ 10 μHz between observed and computed frequencies. In those models, the near-surface region of the star was treated rather crudely: convection was described by means of a local mixing-length theory neglecting turbulent pressure, and the oscillations were assumed to be adiabatic. These approximations are likely to affect both Δv and absolute frequencies.

An analytic theory of resonant transmission has been used to study adiabatic, non-vertical oscillations in a realistic model of the solar or a stellar atmosphere and subphotosphere. Basic observed features of solar p-modes can be explained in this way.

We calculated visibility functions of intensity fluctuations due to adiabatic waves in a realistic model of a non-grey, stratified atmosphere in LTE. The results for different optical wavelengths λ and their angular dependence are discussed; moreover, a method for selecting various low-degree p-modes from observations of spectral irradiance fluctuations at different λ including the UV is suggested.

The first space seismological experiment, EVRIS (Baglin 1991) will be launched in 1996 and will observe ∼ 10 stars over ∼ 20 days each. A second one, COROT (Catala et al., 1994), should follow soon after (1999-2000), which should monitore ∼ 5 stars over ∼ 5 months each. The observed stars will be main sequence stars. For an optimum scientific outcome of EVRIS mission, one must select the best possible target stars. The first step of this selection is outlined. What would be further gained with COROT project is discussed.

Specifications of both missions imply that among possible target stars, δ Scuti stars should present a large number of self excited modes, likely many more than presently observed from ground based networks.

STARS is a proposed asteroseismology (and stellar activity) space mission which is currently under phase A study in the European Space Agency as a candidate for the Medium Size Mission (M3).

It will be possible to make photometric variability studies from space of stars serendipitously falling in the field of view of the Optical Monitor, and to search for asteroseismological phenomena in bright target stars.