Absolute magnitudes of semi-regular variables in the solar vicinity from statistical parallaxes.

Absolute magnitudes of Semi-Regular and RV Tau variables have been determined from radial velocities and proper motions. I.Photographic absolute magnitudes of M-type SRab variables vary with spectral type from 0m.0 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) = 06+39 (logp-2o)andMpg(max) = Ol +28 (logp- o), where p is the period in days. These variables are fainter than the Miras at a given period (Figs I and 2). 3.SRab variables with p <200 days showing emission lines fall on the extension of the period-absolute magnitude relation for Mira variables. There is no significant difference between SRab M and SRab Me variables for 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) = + 0m.7 j 0m.4 5.SRd variables have Mpg(mean) = - 0m.9 j 0m.4 and Mpg(max) = - Im.7 I 0m.4. 6.RV Tau variables have Mpg(mean) = - 0m.5 I o 6 and Mpg(max) = - Im.7 I om.6. The present results have been compared briefly with the absolute magnitudes of similar stars in clusters.