COMMISSION 27 OF THE I.A.U.
               INFORMATION BULLETIN ON VARIABLE STARS
                            Number 1452

                                                      Konkoly Observatory
                                                      Budapest
                                                      1978 July 31


            ON THE PERIOD OF RY SCUTI

The unusual eclipsing system RY Scuti, one of the few
radio binaries, was for decades a rather neglected object.
It was believed that its period was not constant, but the
nature of the period changes--as Wenzel and Gessner recently
(1977) pointed out--remained to a large extent unknown. The
method of estimating the minimum epoch from isolated "faint
observations" is obviously of very little avail, as a plot of
the data from the table of these authors illustrates. They
addressed the owners of other plate collections to try to
fill the gaps.
   The University of Oklahoma plate collection contains 198
plates taken by Professor B. S. Whitney with the 85 mm Zeiss
astrograph which show the variable. The observing seasons
1948 (with 1949), 1955, 1957 and 1958 are well represented
and allow the construction of mean light curves and the derivation 
of normal minima. The plates were measured with the
Coffey iris photometer using a blue photometric sequence, 
derived earlier by Professor Whitney from 14 comparisons with the
NPS.

 Normal epochs for these years are given below.

(1) Min. I = JD 2432796.445   O-C = +0d006
(2)               35366.218   O-C = -0.082
(3)               36078.080   O-C = -0.216
(4)               36433.91    O-C = -0.39 :

   The last epoch is of much less weight, since its value hinges
mainly on two plates taken near phi = 0.86. The O-C values are
calculated from Gaposchkin's elements (1937):

       Min. I = 2427979.34 + 11d.124939 * E

   The figure shows these O-C values (against Gaposchkin's formula) 
together with other normal epochs. We omitted all times of
minima derived from "faint observations", even if based on
scattered photoelectric data. The last point corresponds to a
set of photoelectric observations made in Catania and 
published in a preliminary form (Ciatti et al. 1977); we 
incorporated the observed phase shift -0.06 P into the figure, by
tentatively substituting JD 244297 (Aug. 6, 1976) for the
expression "during summer 1976." The agreement with the adjacent 
Sonneberg normal epoch of the minimum is quite satisfactory.

   There still exists a gap of about 15 years between the
Oklahoma observations and the more recent ones, but the two
groups of minimum epochs can be remarkably well represented
by a single linear formula:

      Min. I = JD 2432796.477 + 11d.124138 * E
                                     (after JD 2432000)

The corresponding O-C values are tabulated below.

E=0     O-C = -0.032d    Oklahoma min. no. 1
E=231         +0.065                   no. 2
E=295         -0.018                   no. 3
E=814   O-C = -0.045     Sonneberg, normal min.
E=917         +0.030     Catania, phe


This representation suggests that
   1. the period of RY Scuti seems to have shown relatively
little change during the past 30 years;
   2. there was a marked change (decrease) of the period some
time around 1938-1942. The derived amount of the period variation 
depends crucially on the early observations discussed by
Gaposchkin (l.c.). Taken these residuals at face value the
net change of the period between 1900 and 1975 turns out to be
of the order of -0d.00104 or -90 sec. It is, however, nearly
impossible to tell whether this change occurred instantaneously
or by continuous decrease.
   A mean light curve for the years 1948-1960 shows a wide
scatter of about 0.25 magn.; this is almost certainly due
mainly to changes in the light curve. While the depth of 
primary minimum did not show conspicuous variations, its shape
varied noticeably, especially in 1957 when it was much narrower
than usual (see also O'Connell 1949).


                    [FIGURE 1]


                      R. A. BRADY and T. J. HERCZEG

                      Department of Physics and Astronomy
                      University of Oklahoma
                      Norman, Oklahoma



[References]
(1) Ciatti, F., A. Mammano, R. Margoni, A. Vittone and G. Strazzulla, 
    1977: Bamberg Veroeff. 11, No. 121, p. 386. [BIBCODE 1977ivsw.conf..386C ]
(2) Gaposchkin, S., 1937: Harvard Obs. Ann. 105, p. 511. [BIBCODE 1937AnHar.105..509G ]
(3) O'Connell, D.J.K.S.J., 1949: A.J. 54, 134. [BIBCODE 1949AJ.....54..134O ]
(4) Wenzel, W. and H. Gessner, 1977: IBVS No. 1276.