Recently, new views of the current status of δ Scuti stars have been developed by Rodríguez & Breger (2001) who carried out an excellent review, listing 8 pre-main-sequence (PMS) δ Scuti candidates and examined the possibility of the existence of PMS δ Scuti variable stars. Here we discuss the nature of 4 stars from their list: 2 said to be members of NGC 2264 and 2 of NGC 6823.

We present new photoelectric observations of the Pre–Main-Sequence δ Scuti star, V351 Ori. These new data suggest that V351 Ori could be a multiperiodic variable. The comparison between observations and detailed pulsational models allows us to put independent constraints on the mass and luminosity of the star. The predicted distance is 210 pc, indicating that V351 Ori is much closer than the Orion star forming region. With an inferred mass of ∼1.8 M⊙ and an uncertain evolutionary stage, V351 Ori represents an excellent candidate for future asteroseismological studies that will assess whether it is a young PMS star (∼6 Myr) or an evolved object (∼1 Gyr) leaving the main-sequence.

The phase space and FFT tools are applied to investigate the irregular behavior of the existing light curves of the λ Boo star 29 Cyg.

We report the discovery of periodicities in the light curve of the Herbig Ae star V346 Ori. We interpret these variations as the superposition of at least two signals with periods P1=42±6 min and P2=68±12 min resulting from stellar oscillations. The computation of linear non-adiabatic pulsation models for Pre-Main Sequence (PMS) stars reproduces these periods for a 1.5 M⊙ star with Teff= 7300 K and log L/L⊙= 0.74, pulsating in the fundamental and second overtones.

A brief overview of the relatively new field of pulsating sdB stars is presented together with some recent observational and theoretical developments. A list of known pulsators is included.

We briefly present a method to perform detailed asteroseismological analyses of pulsating subdwarf B (sdB) stars (also referred to as the EC14026 stars). We use a forward approach based on the computation of large grids of sdB stellar models (each model being analyzed with a linear nonadiabatic pulsation code) to derive, in an objective way, the most appropriate set of model parameters that can best reproduce the observed period spectrum of a given sdB pulsator. We discuss an illustrative application of this method to the pulsating sdB star PG 1047+003, for which we derive the fundamental parameters Teff, logg, Mtot, and Menv.

We present a preliminary analysis of time series photometry on the pulsating subdwarf B star PG 1336-018 acquired as part of two Whole Earth Telescope runs. PG 1336-018 is a multi-mode pulsator with at least 15 periods centered around 175 seconds. It is also an HW Vir-type eclipsing binary with a period of 2.4 hours. Although over 20 pulsating subdwarf B stars have been discovered, only a few have resolved temporal spectra and still fewer have identified pulsation modes. We analyze features unique to the eclipsing binary system of PG 1336-018 as a means of identifying pulsation modes.

We present analysis of rapid spectroscopy of PG 1605+072, a pulsating sdB star that is believed to have evolved off the extreme horizontal branch. Using a cross-correlation technique on five Balmer lines (Hβ to H8), we have been able to study the Doppler variations in this star over one year. Preliminary results for about 25% of the time-series were presented by O’Toole et al. (2000). We find evidence for amplitude variation between 1999 and 2000. We have also examined of equivalent widths of the Balmer lines looking for variation. Preliminary results are intriguing, with the amplitude of the equivalent width oscillations strongly dependent on wavelength.

We have performed high-speed spectroscopy of the pulsating subdwarf B star PG 1605+072. Its radial velocity variations have frequencies similar to those reported from photometric observations. Peak amplitude ratios are different, probably as a result of power shifting between modes over time. Line-shape variations have also been detected.

Photometric data obtained on the DA type white dwarf star G255-2 between 1991 and 1997 were reduced and the pulsation spectrum was explored with the standard process. The further analysis provides 10 normal, probably l = 1, independent nonradial eigenmodes.

We report on preliminary results from time-resolved optical spectroscopy of the He-rich variable white dwarf GD 358.

The pulsating DB white dwarf GD 358 was observed by the Whole Earth Telescope (WET) in 1990, 1994, and 2000. While these observing runs revealed a wealth of pulsation modes, they constitute only three “snapshots” of the behavior of this star. These “snapshots” show that GD 358 has a series of l = 1 modes present in the period range of 420 to 810 seconds, with numerous Fourier Transform peaks at the sums and differences of the l = 1 mode frequencies. In addition, the amplitudes of the l = 1 modes and the sum and difference frequency peaks (which I also call “combination peaks” in this paper) are different in each WET run. These data are not sufficient to determine the time scale of the amplitude changes and whether additional l = 1 modes might be present. For this, we need more frequent data sets, although not necessarily WET data.

New differential time-series observations of the white dwarf BL Camelopardalis were obtained using the B and V filters. It was confirmed that BL Cam is a double star but the effect of the secondary star on the periods is almost negligible. The (O-C) diagram and periods were analyzed.

We examine the severe disagreement between the number of predicted and observed pulsation modes for δ Scuti stars. The selection of nonradial modes trapped in the outer envelope is considered on the basis of kinetic energy arguments. The trapped l = 1 modes for the star 4 CVn are in good, but not perfect agreement with the observations. The trapping of the l = 2 modes is weaker, so that this simple rule of mode selection may apply to l = 1, and possibly not to l = 2 modes.

We discuss the results of a systematic search for multi-periodic pulsations in Galactic Bulge δ Scuti and RR Lyrae stars. Six “normal” double-mode variables pulsating in two radial modes have been identified (5 δ Scuti-type and 1 RR Lyrae-type). In 37 RR Lyrae stars secondary periodicities very close to the primary pulsation frequency have been detected. These periodicities correspond to nonradial modes of oscillation. They are found in ∼ 23% of RRab and in ∼ 3% of RRc variables of our sample.

Recent analyses of photometric data on globular clusters and galaxies enabled us to study more closely the long-periodic amplitude/phase modulation (Blazhko effect) in classical variables. In the frequency spectra of these stars we see either a doublet or an equally-spaced triplet with a very small frequency separation close to the main component. None of the available theoretical models are able to explain this behavior without invoking some form of nonradial pulsation. In this review we describe the observational status of the Blazhko variables, and discuss the limits of the applicability of the current models to these stars.

A recently recognized problem is revisited, namely the discrepancy between the structure of the theoretical and the empirical, observationally derived RR Lyrae instability strips. The essence of the discrepancy is that the slope of the empirical fundamental-mode blue edge is much less steep than its theoretical counterpart. The issue was investigated by means of stellar evolution and mode selection captured by nonlinear models.

The radial pulsations of variable stars at specified points along their evolution are accurately described with numerical hydrodynamics. The behavior of the pulsations along evolutionary tracks can then be modeled with amplitude equations, whose coefficients are obtained from fits to these hydrodynamical models. To simulate stellar evolution we make the stellar core’s properties time-dependent and can investigate directly the effects on pulsation despite the very different time-scales (dynamical, thermal, evolutionary).

A nonlinear development of radial pulsation instability to a resonant excitation of nonradial modes is studied. The theory covers the cases of axisymmetric (m = 0) modes as well as (m, −m) pairs. Adopting a simplified treatment of the mode coupling, it is found that multimode pulsation with constant amplitudes is a highly probable solution. An observable consequence of the m = 0 mode excitation is randomness of pulsation amplitude. The case of an l = 1 mode is the most important because of a small averaging effect and a large excitation probability. A significant amplitude and phase modulation is predicted in the case of excitation of an l = 1, m= ±1 pair. This may explain Blazhko-type modulation in RR Lyrae stars. If this model is correct, the modulation period is determined by the rotation rate and the Brunt-Väisälä frequency in the deepest part of the radiative envelope.

We present the preliminary results of a frequency analysis of 1457 fundamental mode RR Lyrae (RR0) stars in the Large Magellanic Cloud (LMC) from MACHO Project photometry. We find the same classes of pulsational behavior as were found in our earlier survey of first overtone RR Lyrae (RR1) stars. Variables whose prewhitened power spectra contain one or two peaks close to the main frequency component in the original power spectra are commonly known as Blazhko-type variables. The present analysis shows the overall frequency of Blazhko-type stars in the total RR0 population analysed to date to be ≈ 10%. This is lower than the often cited Galactic field/globular rate of 20-30% (Szeidl, 1988).

The incidence rate of Blazhko-type variability in the LMC appears to be about three times higher in RR0 stars than in RR1 stars. This puts important constraints on possible models of the Blazhko effect.