One small satellite, so many light curves: Examples of δ Scuti asteroseismology from the MOST space mission 1

The skies are alive with the sound of music. The symphonies of δ Scuti stars, both postand pre-main sequence, offer more exciting potential for asteroseismology than ever before. Continuous precise light curves of δ Scuti stars obtained by the MOST (Microvariability & Oscillations of STars) space mission offer rich eigenspectra and accurate relative mode amplitudes to test models of stellar structure and nonlinear pulsation dynamics. Many of these δ Scuti pulsators have been discovered among the MOST Guide Star sample. One of them, HD 209775, exhibits more than 80 frequencies, rivalling FG Vir in its richness. The observed amplitude distribution is a test of theoretical mode growth rates and the histogram of frequency spacings places meaningful constraints on the stellar structure and evolutionary phase. MOST has also discovered at least two ”hybrid” pulsators, simultaneously exhibiting both δ Scuti p-modes and γ Doradus g-modes, doubling (or tripling) the number of known hybrids. MOST has also been used to target pre-main sequence pulsators (like those in the cluster NGC 2264), performing ’ultrasound’ of stellar embryos based on the acoustic oscillations.