COMMISSION 27 OF THE I.A.U.
              INFORMATION BULLETIN ON VARIABLE STARS
                           Number 1276

                                                    Konkoly Observatory
                                                    Budapest
                                                    1977 May 12


         PERIOD CHANGE OF THE RADIO BINARY RY SCUTI

In a recent paper Cowley and Hutchings gave an analysis of
tentative radial velocity and spectrophotometry data of this
high-mass eclipsing radio binary (Publ. Astr. Soc. Pac. 88,
p. 456 ff). In their paper they raised the question about the
reliability or constancy of the orbital period given by Gaposchkin
(Harvard Ann. 105, p. 511). Strange enough, this peculiar system
has largely been overlooked by observers of photoelectric light
curves. 
   In order to render possible a modern ephemeris the object
was estimated on Sonneberg sky patrol plates of the years 1970
to 1976. The result is shown by the accompanying mean light curve,
which was computed with the help of Gaposchkin's elements.

       Min. I = 242 7979.34 + 11.124939d E = C

and which rests in the photometric system of O'Connell (Harvard
Circ. 452, p. 9). A phase shift of about -0.06p = -0.66d is clearly
present. Doubtless this arises from a period change, but not
even the search for further faint observations on plates from
1935 to 1969 enabled us to make certain the date or mode of this
change. For the purpose of discussing mass transfer and mass loss
it would be highly desirable that the owners of other plate 
collections contribute to this problem.
   In the table we give (O) the deepest observations of ours
for 1935 to 1969 (E<=+1120.5), our normal minimum (E=+1247) from
the above mentioned estimates of the seventies, normal minima
from Gaposchkin's (1.c.), Tsesevich's (Odessa Izv. 4, 2, p. 356),
Filin's (Stalinabad Tsirk. 67-68), and O'Connell's (l.c.) data,
and a faint photoelectric observation by Hilditch and Hill
(Victoria Contr. 268, p. 122).
   Especially noteworthy is also the variability of the form
of the light curve: Compare Gaposchkin's, O'Connell's and our
curve.

                      [FIGURE 1]

      O          E           O-C
   J.D.24..

1  5519.41      -1120       -0.19d   N    Gaposchkin
2  6599.85      - 124       -0.08    N    Gaposchkin
2  7823.58      -  14       -0.01    N    O'Connell
3  0582.39      + 234       -0.19    S
3  0849.53      + 258       -0.05    S
3  0938.71      + 266       +0.14    N    Tsesevich
3  1238.95      + 293        0.00    N    Filin
3  4653.30      + 603.5     +0.05    S
3  5933.62      + 715       -0.05    S
3  7070.52      + 818       -0.02    S
3  7190.31      + 828       -0.48    S
3  9293.47      +1017       +0.07    S
3  9671.44      +1051       -0.22    S
4  0444.36      +1120.5     -0.47    S
4  1806.92:     +1243       -0.72:   S    Hilditch, Hill
4  1851.48      +1247       -0.66    N    from lightcurve

(N = normal minima, S = single faint observations)


                      W. WENZEL and H. GESSNER

                        Sternwarte Sonneberg
                   Zentralinstitut fur Astrophysik
                 Akademie der Wissenschaften der DDR