ON THE MASS OF TYPE-C RR LYRAE VARIABLES IN GLOBULAR-CLUSTERS

The mass of RR Lyrae variables has been a controversial problem for ab out a decade, as the stellar evolution and pulsation theories predicte d values in significant disagreement. An independent method for estima ting physical parameters of type-c RR Lyrae stars such as mass, lumino sity and temperature was found by Simon (1989, 1990a) and recently rev ised by Simon & Clement (1992a,b). This method makes use of the Fourie r parameter phi31, and we have applied it to a number of RRc stars in globular clusters of both Oosterhoff types, namely M3, M5, M62, NGC320 1, NGC4147, NGC6171, M15, M53, M68 and NGC4833. The average values of mass we have found are M=0.60+/-0.16 M. and 0.67+/-0.19 M., and the lu minosities are logL=1.685+/-0.021 and 1.768+/-0.022 for Oosterhoff typ e I and II clusters respectively. These results are discussed and comp ared with other determinations and the present requirements of the ste llar evolution and pulsation theories. There is a strong indication fo r a brighter zero-point of the luminosity scale by approximately 0.2-0 .3 mag with respect to the results of the Baade-Wesselink method appli ed to field RR Lyrae stars.