COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                      NUMBER 474


                                  Konkoly Observatory
                                  Budapest
                                  1970 October 25


        ANOTHER VARIABLE WITH CHANGING PERIOD

      Magnitudes for one of my hitherto unpublished variable 
stars in Sagittarius, at 18h33m07s - 21d14.2 (1900)
were estimated by Miss Loretta J. Locicero on some 250 Harvard 
and 500 Nantucket plates. For the Harvard plates of
the MF series (10-inch Metcalf, scale 167"/mm) for the
years 1924-34, she found a reciprocal period of 2-d467859,
and for the Nantucket plates (7.5-inch Cooke, scale 248"/mm)
a slightly shorter value, 2.467825. Harvard plates of other
series for the intermediate years 1942-51 are sparsely
distributed and do not fit either of these periods well. In
Figure 1, therefore, I have plotted the phases of ascending
light, on the basis of the reciprocal period, 2.467825 and
for magnitudes brighter than 13,7, against the Julian day
from J.D.2424000 to beyond 2440000. This indicates that the
period in changing progressively. All of the observations
are then satisfactorily represented (Figure 2) by

   Phase = 2.467825 (JD) -n -0.130*10^-8 (JD -2438500)^2.

The final term in this expression is represented by the
smooth curve through the points in Figure 1. In terms of
the period itself we get

   Max = JD 2438563.748 + 0d4052151 n + 0.865.10^-10n^2.


                     [FIGURE 1]

The period and change of period are given by

             P = P_0 (1. + 5.27 * 10^-10 n)
                
representing a progressive lengthening of the period by
1.85*10^-5 seconds per cycle.
      The observations seemed to indicate a possible
secular change in amplitude or magnitude at maximum. This
can, however, be interpreted merely as systematic errors
corresponding to the use of different instruments, different
emulsions, and different effective exposures in a field
where overlapping images are prevalent. The horizontal
spread in the ascending branch of the light curve appears
to be random and does not suggest a correction either to
the basic period or the secular term.
      The insert in Figure 2 is a finding chart showing a
field of approximately 10' x 10'.

                  [FIGURE 2]

        This is a part of the summer work at the Maria
Mitchell Observatory supported by the U.S. National Science
Foundation, for which we should like to express our appreciation.

8 October 1970                  
                                DORRIT HOFFLEIT
                        Maria Mitchell Observatory
                        Nantucket, Massachusetts, U.S.A.