COMMISSION 27 OF THE I. A. U.
          INFORMATION BULLETIN ON VARIABLE STARS
                     Number 1177

                               Konkoly Observatory
                               Budapest
                               1976 September 10



           THE NATURE OF THE VARIABLES IN M13

      Osborn and Rosenzweig (IBVS No 1126, 1976) recently suggested
that available photometry of variable No. 1 in M13 shows the presence 
of a bump in the light curve at a phase which when correlated
with theoretical models (Stobie, Observatory 93, 111, 1973) would 
imply a mass of 0.2M_Sun. In view of the importance of such a result for
understanding the evolution of globular cluster stars we have obtained 
improved photographic photometry of this and other variables in
M13.
    The observational material consists of a series of B & V plates
taken with the 100" Mt Wilson reflector and kindly loaned to us by
Dr Margaret Penston. We have calibrated the plates using the photometry 
of Cathey (A.J. 79, 1370, 1974). The analysis of the V plates is
now complete and the descending branch of the light curve of variable 
1 is well covered by the observations but shows no evidence for
the suggested bump. On the other hand the curve appears to show a
bump on the rising branch which according to the precepts of Stobie
gives R=8.7R_Sun and M = 0.55M_Sun. These are more in line with the 
values normally associated with the later stages of evolution in 
globular clusters.
    Our data have further us to estimate the mean magnitudes of the
RR Lyrae stars, variables Nos. 5, 8 and 9 which we find to be 
significantly fainter than the values adopted by Sandage (Ap.J., 162, 841,
1970). These stars therefore do occur at the magnitude level of the
horizontal branch in M13 and it is no longer necessary to consider
them as extraordinary in this respect.
    Reduction of the data to obtain colours for the variables is
in progress and full details will be published elsewhere.


                      C.D. PIKE and CAROLINE J. MESTON

                        Royal Greenwich Observatory
                        Herstmonceux Castle, Hailsham
                               England.