COMMISSION 27 OF THE I. A. U.
        INFORMATION BULLETIN ON VARIABLE STARS
                    Number 1930

                                 Konkoly Observatory
                                 Budapest
                                 1981 March 9

                                 HU ISSN 0374-0676



             PHOTOELECTRIC TIMES OF MINIMA
                 OF ECLIPSING BINARIES


   The following times of minima have been determined from photoelectric
V-filter observations made using the 40-cm f/18 Cassegrain reflector of the
University of Montana. The observing procedure was the same as that described
in IBVS No. 1478 (Margrave et al., 1978).



Table I.   Heliocentric Times of Primary Minima

Star        Hel.JD-2,440,000       E          O-C          N
KO Aql     	4516.6774          918     +0.0025d       51
RZ Cas   	4152.9197        11945     +0.0005 	  31
          	4451.7293        12195     -0.0017 	  26
          	4476.8307        12216     -0.0005 	  33
          	4507.9058        12242     -0.0018 	  64
TV Cas    	4453.8209         1577     +0.0013 	  69
TW Cas    	4500.8105         1745     -0.0022 	  27
DO Cas    	4451.8248        15373     -0.0045 	  34
          	4477.8494        15411     +0.0028 	  30
          	4516.8723        15468     -0.0002 	  52
AT Peg    	4442.8188         3494     -0.0551 	  50
          	4520.7515         3562     -0.0575 	  49


   A least-squares parabolic fit was utilized to find each time of primary
minimum in Table I, in which are listed the heliocentric Julian Date (minus
2,440,000) for each minimum, its epoch number E, the O-C value, and N, the
number of observations used in the determination. The ephemerides used to
calculate the O-C values are given in Table II.

Table II. Ephemerides for Program Stars

Star         Epoch            Period        Source
KO Aql   2,441,887.4724      2.864055d     IBVS 1869
RZ Cas   2,429,875.6902      1.1952473     Herczeg and
                                           Friboes-Conde
TV Cas   2,441,595.3582      1.8125944     IBVS 1869
TW Cas   2,442,008.3873      1.4283240     IBVS 1869
DO Cas   2,433,926.4573      0.6846661     SAC 51
AT Peg   2,440,438.383       1.146105      SAC 51


   Incorporating the two minima for AT Peg given in Table I into the data
set which was used in IBVS No. 1869, the following updated parabolic ephemeris
is obtained for AT Peg:
   Hel. JD (Min) = 2,440,407.4370 + 1.14610886d E - 5.5772 x 10^-9 * E^2.
This quadratic ephemeris fits all known photoelectric minima back to 1969 with
a mean residual of 0.0017d and implies a continuous period decrease since 1969
of 15.4 seconds per century. The epoch number for the last minimum of AT Peg
in Table I is E = 3589 for the quadratic ephemeris and the residual is +0.0016d.


                            THOMAS E. MARGRAVE

                            Blue Mountain Observatory
                            University of Montana
                            Missoula, Montana 59812
                            USA


References:
Herczeg, T. and Friboes-Conde, H. 1974, Astr. and Ap., 30, 259. [BIBCODE 1974A&A....30..259H ]
Margrave, T. E. et al. 1978, IBVS No. 1478.
Margrave, T. E. 1980, IBVS No. 1869.                                 
Rudnicki, K. 1979, Supplemento ad Annuario Cracoviense No. 51, Krakow. [BIBCODE 1979raok.book.....R ]