Probing rotation in pulsating stars from space

Abstract

At the time of the last Stellar Rotation symposium in 1969, the map of known pulsators in the H-R Diagram covered a lot less territory, being confined mainly to the classical instability strip. Among the new classes of pulsators are the strongly magnetic roAp (rapidly oscillating Ap) stars whose pulsation amplitudes and phases are modulated with their rotation periods. Among the classical pulsators, the δ Scuti stars are now known to show many more eigenmodes and frequency splitting than was ever recognised three decades ago. Both are examples of the diagnostic potential and severe challenges to detect and interpret correctly rotational fine structure in the pulsational frequency spectrum. In a pulsating star, rotation can perturb the structure or dynamics, and it can split degeneracies to serve as a diagnostic of pulsational modes. One tool which should help us exploit the potential and overcome the challenges of studying the interaction between rotation and pulsation is Canada's MOST (Microvariability & Oscillations of STars) microsatellite. MOST is a small optical telescope and ultraprecise CCD photometer designed to detect and characterise acoustic (p-mode) oscillations with periods of minutes and amplitudes as low as 1 micromagnitude in bright stars. While customised to conduct asteroseismology of solar-type stars, the MOST mission will also include roAp stars as prime targets and eventuallly δ Scutis as secondary targets. I present here simulations of MOST observations of such targets with different rotation periods, in advance of the real data expected in the months after the scheduled 30 June 2003 launch.