COMMISSION 27 OF THE I. A. U.
          INFORMATION BULLETIN ON VARIABLE STARS
                       Number 952

                                     Konkoly Observatory
                                     Budapest
                                     1974 December 13


                 A NEW VARIABLE STAR IN M13

    Two bright stars in the globular cluster M13 = NGC 6205 have recently
been suspected by Russev (Astr. Zh, 51, 122, 1974) to vary in brightness.
The two suspected variables are stars 414 and 973 in Ludendorff's 
catalogue (Publ. Potsdam Obs. 15, no. 50, 1905), the corresponding Kadla (Iz.
Pulkova Obs, 24, 92, 1966) and Arp (Astr. J. 60, 317, 1955) numbers being
K444 = Arp III-56 for L414 and K544 = Arp I-48 for L973. Both of the stars
are bright red giants with B-V ~ 1.5 and therefore could be possible members 
of the semi-regular class of cluster variables about which little is
known.
   We have investigated the variability of these two stars on the plates
of M13 at our disposal. Our methods for testing the reality of the 
variability were the same as those used previously (IBVS 798, 1973; IBVS 849,
1973). Briefly, the B magnitudes of the two suspects were determined in
relation to a sequence of comparison stars using a Becker type iris 
photometer. As a control, two non-variable stars close to and of approximately
the same brightnesses as the two suspects were also measured and were 
reduced in the same manner as for the possible variables.
   We found no evidence that L414 varied during the three years covered
by our observations. The magnitudes from the 56 plates were distributed
in roughly Gaussian fashion about the mean value of 13.65 with a dispersion 
of 0.05 mag. Our mean value agrees well with the B magnitude given
by Kadla. The dispersion in the measures is identical to that found for
the two control stars (as well as in agreement with the results found in
our previous investigations using the same plate material) and thus can be
entirely explained as due to random measuring errors. We conclude that
within the accuracy of our measures L414 does not vary.

   Measurements of L973 are difficult due to the presence of two close
companions about three magnitudes fainter and some of our measures have
probably been affected by these stars. Nevertheless, our observations
indicate that L973 definitely varies over a range of about 0.4 magnitudes.
Our mean B of 13.50 differs by 0.12 mag. from Kadla's value, while the
histogram of the measures is non-Gaussian with a dispersion of 0.14 mag.,
significantly greater than that for the other stars. The available 
observations can be approximately represented by a period near 39d but the
light curve shows the irregular behavior characteristic of semi-regular
variables. The variations of L973 for the three years covered by our
plates is shown in the figures. Variable stars with periods of the order
of 40d ar very rare in globular clusters and further studies of this star
would be worthwhile.

   The details of our studies of the M13 variables will be published
elsewhere. We wish to thank M. Ibanez for permission to re-reduce his
measures of L414 made for another purpose and the U.S. Naval Observatory
for the observing time during which the plates were taken.



FRANCISCO FUENMAYOR                         WAYNE OSBORN
Facultad de Ciencias                        Inst. Venezolano de Astronomia
Univ. de Los Andes                          Apartado 264
Merida, Venezuela                           Merida, Venezuela


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