Physical parameters of the semiregular variable red giant 2 Cen

This is a study of photometric data from the Hipparcos catalog and spectrophotometric observations by a group of Pulkovo observers in Bolivia of the variable star 2 Cen (V806 Cen). Fourier analysis yields a more precise value of 12.57 d for the period of the brightness variation instead of 12.0 d. Light curves constructed from the photometric data are found to have a smooth systematic variation with an amplitude on the order of 0^m.2. Short duration changes in the brightness by 0^m.1 take place over times of a few hours. The differences in the temperature and radius of the emitting layer at maximum and minimum brightness, which occur at phases of 0.00 and 0.58, respectively, are found. At the maximum the radius was smaller by 6% and the temperature was higher by 70 K; these differences may characterize the star’s pulsations.