COMMISSION 27 OF THE I. A. U.
      INFORMATION BULLETIN ON VARIABLE STARS
                  Number 1631

                                  Konkoly Observatory
                                  Budapest
                                  1979 June 25


        PHOTOELECTRIC MINIMA OF FIVE ECLIPSING

         BINARIES IN CASSIOPEIA AND PEGASUS




   During the summer and fall of 1978 photoelectric V-filter
observations were made of primary minima of DO Cas, RZ Cas, TV Cas,
TW Cas, and AT Peg with the 40-cm Cassegrain telescope of the University 
of Montana. The observing procedure was the same as described
in IBVS No. 1478 (Margrave et al., 1978).                                 

      Table 1. Observed Heliocentric Times of Minima


Star     Hel. JD - 2,440,000          O-C

DO Cas   3728.8184 +- 0.0003         -0.0013d
         3795.9144 +- 0.0003         -0.0026
RZ Cas   3723.8235 +- 0.0003         -0.0019
         3729.8003 +- 0.0002         -0.0014
         3760.8740 +- 0.0004         -0.0041
         3772.8246 +- 0.0002         -0.0060
         3790.7519 +- 0.0001         -0.0074
         3796.7303 +- 0.0002         -0.0052
         3803.9019 +- 0.0003         -0.0051
TV Cas   3786.7774 +- 0.0002         -0.0178
         3795.8442 +- 0.0003         -0.0140
TW Cas   3803.7904 +- 0.0005         -0.0029
AT Peg   3728.7993 +- 0.0010         -0.0512


   The times of minima in Table 1 were determined both by the chord
bisection method and by the least-squares fitting of a parabolic
curve. The results given by the two methods are usually the same
to four decimal places. When they differ by amounts of the order
of the quoted standard deviations, the least-squares quadratic fit
result is given here.
   The ephemerides used to calculate the O-C values are given in
Table 2. The large negative residuals for TV Cas are consistent with


        Table 2. Ephemerides for Stars Observed


Star       Hel. JD        Period (days)   Source

DO Cas   2,433,926.4573   0.68466595      SAC 50
RZ Cas   2,429,875.6902   1.1952473       Herczeg and
                                          Friboes-Conde
TV Cas   2,443,043.6265   1.8126066       SAC 50
TW Cas   2,442,008.3850   1.428328        SAC 50
AT Peg   2,440,438.383    1.146105        SAC 50


the trend of early-occurring eclipses evident in the data of Pohl
and Kizilirmak (1976) and Ebersberger, Pohl, and Kizilirmak (1978).
A more accurate ephemeris for the prediction of future primary minima
of TV Cas is

           Hel. JD (Min) = 2,442,590.4728 + 1.81258632d E.



This ephemeris gives residuals less than 0.0025 days for the minima
of the two notes cited above and the present note but is not intended
as a definitive new ephemeris for TV Cas.


   The very large negative O-C value for AT Peg found here continues
the trend to early-occurring eclipses noted by Margrave et al. (1978).
It would appear that the period decrease of AT Peg has accelerated
since 1975. The following quadratic ephemeris is suggested for 
prediction of future primary minima of AT Peg:

         Hel. JD (Min) = 2,440,438.3819 + 1.14611546d E

                    - 9.523 x 10^-9 E2.



This ephemeris is based on observations only back to 1969, for which
it gives a mean residual of 0.0030 days, and is intended merely to 
aid observers in planning observations of AT Peg. It is obvious,
however, that careful attention should be given to deriving a revised
ephemeris for this star.


                          T. E. MARGRAVE
                          Blue Mountain Observatory
                          University of Montana
                          Missoula, Montana 59812
                          USA





References:

Ebersberger, J., Pohl, E., and Kizilirmak, A.: IBVS No. 1449, 1978.
Herczeg, T. and Friboes-Conde, H.: Astr. and Ap., 30, 259, 1974. [BIBCODE 1974A&A....30..259H ]
Margrave, T. et al.: IBVS No. 1478, 1978.
Pohl, E. and Kizilirmak, A.: IBVS No. 1163, 1976.
Rudnicki, K.: Supplemento ad Annuario Cracoviense No. 50, Krakow 1978. [BIBCODE 1978raok.book.....R ]