Super-Nyquist Asteroseismology

Photometric observations from space missions have provided us excellently uninterrupted continuous data taken over long timespans with ultra-high precision and made it possible for us to investigate seismically the deep layers of the Sun and the stars. Due to a telemetry limit of space missions, however, the sampling cadence of photometry is not freely set as we would like to have. A typical case is 30-min sampling of the Long Cadence mode of the Kepler Space Telescope. Many stars, including A type stars, are oscillating with shorter periods than this sampling, and consequently the Nyquist aliases of oscillations trouble in data analysis. In my talk, I will first briefly remind you that super-Nyquist asteroseismology was successfully carried out with the original Kepler mission, and then propose a new technique for future missions to overcome the problem of Nyquist aliases. The method only has to introduce modulation to the sampling program in advance. Some suitable combinations of the modulation frequency and amplitude allow us to identify the real oscillation frequencies correctly. I will demonstrate its efficiency and show this method must be useful for future space photometry missions