COMMISSION 27 OF THE I. A. U.
       INFORMATION BULLETIN ON VARIABLE STARS
                    Number 769

                                    Konkoly Observatory
                                    Budapest
                                    1973 February 22



          THE PERIOD OF VARIABLE 7 IN M13


    Arp, in the course of his work on the color-magnitude
diagram of M13 = NGC 6205, found that his observations of
Variable 7 of this cluster could be fitted with a period of
0.2388d (Arp 1955, Astron. J. 60, 317). Recently, however,
Demers (1971, Astron. J. 76, 445) has questioned this period,
finding that it did not represent well his magnitude measures
from plates taken to determine the UBV colors of the M13 
variables. But because his data, as well as Arp's, was very 
limited for a period determination he did not try to find a 
better value.
    In an attempt to clarify the situation we have measured
the brightness of Variable 7 with an iris photometer on the
57 blue plates of M13 at our disposal. As the star was found
to show considerable variation within a few hours, the period
is obviously short and we therefore used the method of Lafler
and Kinman (1965, Astrophys. J. Suppl. 9, 216) to search for
the possible periods in the range 0.20 to 0.33 d. We found
that for this range only two periods which differ by one in
their reciprocals) will fit our data: 0.23803 d. and 0.31293 d.
While the former period is close to that derived by Arp, we
prefer the larger value because, first, periods of this order
are more common and, second, it produced a light curve with
significantly smaller scatter. In addition, the longer period
fits Demer's U,B, and V observations within the uncertainties
expected from photographic photometry. Thus, the characteristics 
of Variable 7 as derived from our observations are:
Period = 0.312929d, Epoch of maximum: JD 24 40051.763, Mean B
magnitude = 15.15, and Amplitude = 0.35 mag.
    The details of this study will be published elsewhere
along with the results for the other variables in this cluster.


    MIGUEL IBANEZ           WAYNE OSBORN

    Dept. de Fisica      Inst. Venezolano de Astronomia
    Univ. de Los Andes   Apartado 264. Merida, Venezuela
    Merida, Venezuela