MONS is a proposed space mission to study stellar oscillations. We briefly describe the main features of the mission – more details are available at the MONS Home Page (http://www.obs.aau.dk/MONS)

MOST (Microvariability & Oscillations of STars / Microvariabilite et Oscillations STellaire) is a Canadian microsatellite mission intended to detect rapid photometric oscillations at the μmag level in stars brighter than V ∼ 6. This limit is set primarily by the 15-cm aperture of the MOST telescope. The small size and mass of the MOST bus (similar to a suitcase) sets a limit on the pointing accuracy of about ±10 arcsec. To achieve the required photometric precision under these conditions, the MOST focal plane features a set of Fabry microlenses which can spread the target starlight into a pupil image of the telescope onto a CCD. The large size (∼1600 pixels) and positional stability (±0.1 pixel) of these images makes MOST insensitive to CCD flat-fielding errors. MOST is currently on schedule to be launched in early 2002.

The Full-sky Astrometric Mapping Explorer (FAME) is designed to perform an all-sky, astrometric survey with unprecedented accuracy. It will create a rigid astrometric catalog of 4 × 107 stars with 5 < mV < 15. For bright stars, 5 < mV < 9, FAME will determine positions and parallaxes accurate to < 50 μas, with proper motion errors < 50 μas/yr. For fainter stars, 9 < mV < 15, FAME will determine positions and parallaxes accurate to < 500 μas, with proper motion errors < 500 μas/yr. It will also collect photometric data on these 4 × 107 stars in four Sloan Digital Sky Survey colors. NASA selected FAME to be one of five MIDEX missions funded for a concept study. In October 1999, NASA selected FAME for launch in 2004 as the MIDEX-4 mission in its Explorer program.

The MOA Project is a collaboration of Japanese and New Zealand (NZ) astronomers and physicists undertaking a survey of stellar variability in the direction of the Galactic bulge and Magellanic Clouds. The primary motivation of the project is detection and monitoring of gravitational microlensing events although a large amount of data is also collected on stellar variability. Surveying the number of stars required to detect gravitational microlensing events is an operation of some magnitude and requires sophisticated data processing software.

A large database of CCD photometry for 1.4 million stars towards both the LMC and the SMC, which has been established by the MOA project, is a useful resource to study variable stars. In our preliminary study, variables identified as β Lyrae type stars and Herbig Ae/Be stars have been found amongst blue stars.

To reach lower noise levels with the Hubble Space Telescope Fine Guidance Sensors (FGS) the photometric properties as well as the systematic effects affecting the data have been investigated.

A significant improvement of the relationships between observed and physical properties of high amplitude δ Scuti stars (HADS), SX Phe stars, and RRc stars can be obtained by the systematic application of Fourier decomposition to their light curves.

A synopsis of mathematical models describing different types of variability and their application to some classes of stars is given.

A review of the properties of Type II Cepheids and RV Tauri stars in the Magellanic Clouds is presented. In the behaviour of their light and colour curves, the RV Tauri stars appear to be a direct extension of the Type II Cepheids to longer periods. A single P – L – C relationship describes both the Type II Cepheids and RV Tauri stars in the LMC. The derived high intrinsic magnitudes for the RV Tauri variables supports the proposition that these objects are luminous stars evolving off the AGB. Preliminary analysis of the long time-series MACHO photometry indicates one star (MACHO*05:37:45.0–69:54:16) has an obvious ‘period-quadrupled’ periodicity, which is supporting evidence for a period-doubling bifurcation transition to chaotic pulsations.

We used wavelets to investigate period and amplitude changes in Mira and semiregular variables and found a variety of behaviours. Period and amplitude changes often go together, perhaps because changes in amplitude are causing period changes via nonlinear effects.

A number of M giant stars with periods of the order of a few days were discovered by the Hipparcos mission. Similar stars may also have been found by other large-scale surveys. Parallaxes and colour indices of a sample of these stars were used to estimate their radii, temperatures and luminosities. It is shown that it is very unlikely that they are ellipsoidal or spotted variables, and that they are most likely pulsating in high overtone modes.

We present the preliminary results of a detailed theoretical investigation on the pulsation properties and modal stability of red supergiant (RSG) stars at solar chemical composition and for stellar masses ranging from 10 to 20 M⊙. We find that the main parameter governing their pulsation behavior is the effective temperature, and indeed when moving from the blue edge toward lower effective temperatures the models show an increase in the pulsation amplitudes. For temperatures cooler than 3800 K the pulsation amplitudes are still large but the radial displacements become aperiodic.

We present the results of various nonlinear radial pulsation calculations of LBVs with different luminosity to mass ratios. Depending on the stellar parameters, most of these objects undergo strongly non-adiabatic pulsations which can also modify their stellar atmospheres. In some cases part of the kinetic energy of the motions is transferred by shock waves into the atmospheric layers leading to an overall decrease or increase of the stellar radius. This results in different mean density accompanied by a change of the pulsational behavior which can be compared to the results of a linear stability analysis. We also find that regular pulsations can occur around a different equilibrium than the initial configuration which has been determined by stellar evolution calculations. In cases of even higher luminosity to mass ratios the linear stability analysis predicts several unstable modes and the nonlinear computations can exhibit rather irregular light curves. Due to the large non-adiabaticity of the pulsation the corresponding velocity curves still remain more regular, but show increasing amplitudes until the energy stored is released. The pulsations are far from equilibrium conditions and may also lead to a pulsationally driven mass loss for certain stellar parameters.

R Coronae Borealis (RCB) stars are a rare class of variable stars, well-known by their declines, but still posing two fundamental questions: what is the origin and what is the nature of their unpredictable minima? Possible contributions to the answering of these questions could use large-scale surveys, by discovering new RCB stars. In addition, photometric databases from these surveys and other long-term photometric programs of targeted stars can be used to compile information about these decline phases.

The photometric observations (UBVRI) of nine cool RCB stars have been collected at Mt John University Observatory, New Zealand, for the last ten years. Analysis of the magnitude–color diagrams for the recovery phase of a number of declines of these stars has been made in order to determine the extinction properties of the dust. The photometric magnitudes and colors show significant changes during the RCB declines. The asymptotic approach to the normal brightness can be seen on the magnitude–color diagrams from the recovery phase. This is observed for all RCB declines, and without exception is independent of their decline amplitude. According to the most acceptable theory, the distribution of the dust matter in the cloud which causes the light fading can be considered uniform as the stars recover to the maximum brightness. The slopes of the magnitude–color and color–color diagrams from the recovery phase of 26 observed RCB declines have been used in order to define the normalized extinction quantity Aλ/AV. Although the extinction curve in the UBVRI region is not a good indicator of the type and size of the particles, our data show that the material causing the RCB declines has extinction properties similar to that for the interstellar medium. The reddening parameter (RBV = AV/E(B – V)) for the RCB stars in our sample is in the range 2.5 to 4.6, similar to the interstellar dust. Observations have been compared with the theoretical extinction curves for different sorts of grains. The extinction properties in the U region follow the trend of the UV data from other RCB observations as well as laboratory data for amorphous carbon.

An extensive search has been made in the MACHO photometry database for new R Coronae Borealis (RCB) stars in the LMC. Only three such stars were known previously. Nine new LMC RCB stars have been spectroscopically confirmed so far.

Preliminary results from a low-resolution spectroscopic survey of RV Tauri stars and Type II Cepheids in the LMC are presented.

We present a progress report on a detailed analysis of long-term (70–90 years) visual observations for seven semiregular variables. Fundamental changes of the physical state (amplitude and/or frequency modulations, mode change and switching) are studied with conventional Fourier- and wavelet analyses. Besides two examples of repetitive mode changes we report a simple geometric model of a rotationally induced amplitude modulation in RY Ursae Majoris.

It is proposed to split the SRc class into two subclasses with prototype stars PZ Cas and S Per.

The red variables whose amplitude is larger than 1.3 mag in the MOA database are studied for the LMC. Among 3 196 such stars, 532 stars are likely to be Miras or red semiregular variables. The period–colour relation of these stars is shown.

We made multicolor linear polarimetric observations of RV Tauri stars using the 91-cm reflector at the Dodaira Station of the National Astronomical Observatory in Japan. We report the main results for 17 RV Tauri stars obtained until now.