Pulsating pre-main-sequence (PMS) stars afford the earliest opportunity in the lifetime of a star to which the concepts of asteroseismology can be applied. PMS stars should be structurally simpler than their evolved counterparts, thus (hopefully!) making any asteroseismic analysis relatively easier. Unfortunately, this isn't necessarily the case. The majority of these stars (around 80) are δ Scuti pulsators, with a couple of γ Doradus, γ Doradus – δ Scuti hybrids, and slowly pulsating B stars thrown into the mix. The majority of these stars have only been discovered within the last ten years, with the community still uncovering the richness of phenomena associated with these stars, many of which defy traditional asteroseismic analysis.

A systematic asteroseismic analysis of all of the δ Scuti PMS stars was performed in order to get a better handle on the properties of these stars as a group. Some strange results have been found, including one star pulsating up to the theoretical acoustic cut-off frequency of the star, and a number of stars in which the most basic asteroseismic analysis suggests problems with the stars' positions in the Hertzsprung-Russell diagram. From this we get an idea of the\break constraints — or lack thereof — that these results can put on PMS stellar evolution.

We have measured transit times for HD 189733 passing in front of its bright (V = 7.67) chromospherically active and spotted parent star. Nearly continuous broadband photometry of this system was obtained with the MOST (Microvariability & Oscillations of STars) space telesope during 21 days in August 2006, monitoring 10 consecutive transits. We have used these data to search for deviations from a constant orbital period which can indicate the presence of additional planets in the system that are as yet undetected by Doppler searches. We find no variations above the level of ±45 s, ruling out planets in the Earth-to-Neptune mass range in a number of resonant orbits. We find that a number of complications can arise in measuring transit times for a planet transiting an active star with large star spots. However, such transiting systems are also useful in that they can help to constrain and test spot models. This has implications for the large number of transiting systems expected to be discovered by the CoRoT and Kepler missions.

Rapid progress in photorefractive polymers includes new materials with improved response rates. We briefly review recent developments in this rapidly evolving area and report grating formation with a 2-millisecond time-constant, the fastest reported to date in any photorefractive polymer.

We present a study of the effects of diffusion of helium and heavy elements from the convection zone into the radiative layer immediately below the convection zone, on the structure of the solar envelope. A comparison is made of the p-mode oscillation spectrum and the run of the speed of sound in a model with diffusion, in a standard model, and with observation.

In a previous paper on Procyon A, we analyzed the best available observational data (summarized here in Table 1), discussed its evolutionary status in terms of theoretical evolutionary tracks, and evaluated on the basis of these models its expected characteristic p-mode frequency spacing (Demarque and Guenther 1986). We reached the following conclusions:

1. (1) that the published astrometric mass of Procyon A is inconsistent with stellar models and seems too large by about 15 per cent.

2. (2) that evolutionary models have too high effective temperatures unless convective overshoot at the edge of the convective core, of the order of a tenth of a pressure scale height, is taken into account.

3. (3) that the p-mode characteristic frequency spacing for Procyon A should be in the range 25–30 μHz.

The aim of this paper is to explore theoretically the potential ability of the p-mode and g-mode non-radial oscillation spectrum to throw light on two fundamental problems raised by our first study: Procyon A's evolutionary status, and its mass-luminosity relation.

Because Epsilon Eridani (Z = 0.013) appears about 0.2 mag above the Z = 0.02 zero-age main sequence, zero-age models of Epsilon Eridani must be evolved off the ZAMS to ages much older than its rapid rotation and high chromospheric activity suggests. To resolve this conflict we propose that either Epsilon Eridani is part of a binary system or that its metal content has been underestimated. To test these hypotheses we use not only the stellar constraints of luminosity and effective temperature but also impose that the characteristic frequency spacing of the oscillation spectra of the models match the value observed by Noyes et al. (1984).

We present here some initial results of a long-term investigation of resonant three-wave interactions in the solar interior, which indicate that these nonlinear interactions take place in the sun and are, in fact, responsible for the observed g mode spectrum. Resonant three-wave interactions, as the name implies, involve the coupled interaction of three waves which satisfy the resonant condition where ω0, and ω1 are the frequencies of the three waves. Two of the waves, mode 0 and 1 for example, couple together to produce a third beat wave which has a frequency equal to the frequency difference of the first two waves. This wave is normally very weak. If its frequency happens to equal the frequency of an oscillation mode of the sun, the wave can be pumped by resonance to very large amplitudes. In the sun, resonant interactions would take place if three natural oscillation modes of the sun satisfy the resonance condition.