Period and amplitude variations of Polaris.

A reinterpretation of the pulsational O-C residuals for Polaris (α UMi), combining photometric and radial velocity observations, shows that the pulsational period has been steadily increasing for the last 100 years, with a period increase rate of 316 s per century. The O-C residuals from this ephemeris are significant, and cannot be explained by light-time effects caused by the orbital motion of Polaris around its unseen companion, or by gravitational effects of the companion at closest approach. The photometric amplitude and the pulsational radial velocity amplitude have decreased since the 1940s. These phenomena may be related to the star leaving the instability strip.