1999JAVSO..27..122M

The pulsating red giant AG Ceti was observed by the observers in the AAVSO photoelectric photometry program, and by the Hipparcos satellite. The data have been analyzed using light curves, autocorrelation diagrams, Fourier transforms, and phase diagrams. The AAVSO data show seasonal gaps, and the Hipparcos data are also distributed non-uniformly in time; we discuss the effects of these time distributions on the results. Autocorrelation analysis of the AAVSO data clearly shows a period of 60-80 days; this is confirmed by the Fourier analysis (period about 77.7 days), the phase diagram, and by the light curves. Evidence for this period in the Hipparcos data is much less clear; periods of 1 to 6 days are also suggested. The difference between the two sets of results may be due to the fact that the AAVSO data were obtained with a V filter, which is very sensitive to pulsational temperature variations in red giants, whereas the Hipparcos data were obtained with a very broad-band filter. AG Cet may be a binary with a pulsating red giant component, and a hotter, bluer component with a short period.