ABSOLUTE MAGNITUDES OF SEMI-REGULAR VARIABLES IN SOLAR VICINITY FROM STATISTICAL PARALLAXES

Absolute magnitudes of Semi-Regular and RV Tau variables have been determined from radial velocities and proper motions. 1.Photographic absolute magnitudes of M-type SRab variables vary with spectral type from om-o at about M4 to + 2m'5 at M6 at mean brightness (Fig. 3). 2.Absolute magnitude of M-type SRa and b variables without emission is a function of period. Mpg at mean and maximum brightness may be expressed asMpg(mean) = o-6 + 3-9 (log p — 2-0) and Mpg(max) = 0-1+2-8 (log p -2-0), where p is the period in days. These variables are fainter than the Miras at a given period (Figs 1 and 2). 3.SRab variables with p 200 days. 4.The mean absolute magnitude of N-type semi-regular variables has also been determined from differential galactic rotation. The combined mean value is Mpg(max) = +om-7±om-4. 5.SRd variables have Mpg(mean) = -om-9±om-4 and Mpg(max) =lim-7 ±om-4. 6.RV Tau variables have Mpg(mean) = -om-s±om-6 and Mpg(max) =lim-7 + om-6. The present results have been compared briefly with the absolute magnitudes of similar stars in clusters. © Royal Astronomical Society