Photoelectric observation of AD Canis Minoris and the change in its period

I have carried out a large amount of photoelectric observation in the V-band on AD CMi. Small variations in maximum and minimum lights are found. A combined analysis of the 12 maximum times I determined and those by previous workers shows that the pulsation period of this star is continually increasing at a rate equal to (1.89 ± 0.09) × 10^?8 d/yr. From its position in the “amplitude-period” diagram, it is inferred that this star has been pulsating for at least 8.6 million years.