COMMISSION 27 OF THE I. A. U.
          INFORMATION BULLETIN ON VARIABLE STARS
                      Number 1191

                                   Konkoly Observatory
                                   Budapest
                                   1976 October 21


     THE BUMP IN THE LIGHT CURVE OF VARIABLE 1 IN M13

   Pike and Meston (IBVS No. 1177, 1976) report that they
have examined a series of V plates of the globular cluster of
M13 and found that Variable 1 of the cluster shows a bump on
the rising branch of the light curve. They conclude, however,
that this feature is not the same as the bump that Osborn and
Rosenzweig (IBVS No. 1126, 1976) suggested was present. In fact,
these two bumps are identical. Osborn and Rosenzweig's bump was
found to occur at phase 0.8 after maximum light, that is on the
rising branch of the light curve at phase 0.2 before maximum.
Using Stobie's (Observatory 93, 111, 1973) equation (1) and Pike
and Meston's derived value for the radius of M13 Variable 1 it
is easy to show that their bump occurs at phi_v= 1.49, which is
equivalent to phi_l = 0.3 on the light curve adopting Stobie's 
relation that phi_v = phi_l + 0.2. That this is on the rising branch of
the light curve implies that their phases are referred to minimum, 
rather than maximum light as in the case of Osborn and
Rosenzweig. Thus, their bump also occurs about phase 0.2 before
maximum and the differences in the derived masses and radii are
therefore just due to the 0.5 difference in the phase systems.
   This author found Stobie's explanation of how the phase
should be determined somewhat confusing and the more common 
reference to the maximum was adopted. However, comparison of
Stobie's listed values of phi_l with the published light curves
for the respective stars shows his equations are for phases 
referred to minimum and hence Pike and Meston's results for the
mass and radius should be preferred.




                         WAYNE OSBORN
                         Physics Department
                         Central Michigan University
                         Mt. Pleasant, Michigan 48859,
                         U.S.A.