COMMISSION 27 OF THE I. A. U.
        INFORMATION BULLETIN ON VARIABLE STARS
                     NUMBER 798

                                   Konkoly Observatory
                                   Budapest
                                   1973 May 25


      CONCERNING A SUSPECTED VARIABLE STAR IN M13


   In 1964 Tsoo Yu-Hua of the Purple Mountain Observatory 
announced that he suspected two stars in the neighborhood of the
globular cluster M13 to be low amplitude variables (reported in
the Draft Reports of IAU General Assembly XIII, p. 556). One of
these stars, Savedoff A-18 (Savedoff 1956, Astron.J. 61, 254) is
sufficiently close to the cluster that it could possibly be an
outlying RR Lyrae member. This star has been denoted Variable 16
of the cluster in the Third Catalogue of Variable Stars in Globular 
Clusters (Sawyer Hogg 1972, preprint). If the variability
and membership were confirmed the star would be of interest both
because only a small number of RR Lyrae stars are known for M13,
and because with a color index of -0.19 as found by Savedoff, which
corresponds to approximately B-V = 0.0, the star would be unusually 
blue for a variable. This is of importance because the blue
edge of the instability region for a cluster depends on the cluster's 
helium abundance.
   As part of our investigation of the short period variables of
M13 we have measured the brightness of Savedoff A-18 on the 57
blue plates of the cluster at our disposal. The measures were made
with an iris photometer in relation to four nearby comparison stars.
As a control, the non-variable star Savedoff A-328, which is of 
aproximately the same brightness as A-18, was also measured and 
magnitudes determined in the same manner as for the suspected variable. 
We find that during the three years covered by our plates the
star A-18 did not vary within the accuracy of our measures, i.e.
the variations if any were less than 0.15 mag. The standard deviation 
for our measures of A-18 with respect to the mean is +0.05mag.,
identical to the value found for the control star. In both cases
the individual values are distributed in roughly Gaussian fashion
about the mean value, whereas measures from the same plates of the
confirmed low amplitude variable, Variable 7, have a distinctly non-
Gaussian distribution. Thus, the present results taken together with
the very blue color index indicate that the star is probably not 
variable.



WAYNE OSBORN                   MIGUEL IBANEZ

Inst. Venezolano de Astromia   Physics Department
Apartado 264                   Univ. de Los Andes
Merida, Venezuela              Merida, Venezuela