COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                     Number 1869

                                    Konkoly Observatory
                                    Budapest
                                    1980 November 15

                                    HU ISSN 0374-0676


           REVISED BLUE MOUNTAIN OBSERVATORY TIMINGS



   Recent reports (Chambliss et al. 1979; Olson 1980) have shown that
published eclipse timings of RZ Cassiopeiae from the Blue Mountain Observatory 
(Margrave et al. 1975; Margrave 1978) are systematically earlier than
those of most other observers. The search for the cause of these discrepancies 
has resulted in the elimination from the computer program used to reduce
the photometry data of two problems which gave rise to systematic errors in
the calculated Heliocentric Julian Dates of the observations. It was the nature
of the two problems that they generated errors sometimes of the same sign and
sometimes of opposite sign. The net effect varied from star to star and from
week to week.
   Consequently, all published eclipse timings (Margrave et al. 1975; Margrave
1978; Margrave 1979a; Margrave 1979b) and times of maxima of BW Vulpeculae
(Margrave and Mefford 1975; Margrave 1979c) have been recalculated and are
given in Table I. The ephemerides used to calculate the residuals for the
eclipsing binaries are the same as those used originally, while that used for
BW Vulpeculae is from Tunca (1978).

   The revised minima of RZ Cas are in complete accord with the trend illustrated 
by Chambliss (1979). A period decrease between September 1975 and September 
1976 is exhibited by the Blue Mountain photoelectric times of minimum
light. There are three RZ Cas minima in common with those of Olson (1980),
namely, 3796.7352, 4121.8434, and 4127.8197, for which the differences in the
sense (Olson - Margrave) are -0.0003d, -0.0002d, and -0.0007d, respectively. The
revised minimum of AT Peg at 2661.8136 is also now in accord with the other




Table I. Revised Heliocentric Julian Dates


Star       Hel.JD - 2,440,000            O-C
KO Aql     2637.8563                   +0d0090
           4135.7552                   +0.0202
44 i Boo   2619.8309                   -0.0011
RZ Cas     1954.8616                   +0.0022
           2339.7312                   +0.0022
           2633.7617                   +0.0018
           2664.8386                   +0.0023
           2670.8163                   +0.0038
           3049.7055                   -0.0004
           3723.8240                   -0.0014
           3729.8012                   -0.0004
           3760.8786                   +0.0005
           3772.8299                   -0.0007
           3790.7582                   -0.0011
           3796.7352                   -0.0003
           3803.9071                   +0.0001
           4096.7436                   +0.0010
           4121.8434                   +0.0006
           4127.8197                   +0.0007
TV Cas     3786.7841                   -0.0111
           3795.8481                   -0.0101
           4094.9264                   -0.0119
           4114.8657                   -0.0113
TW Cas     2666.8447                   +0.0005
           3096.7675                   -0.0034
           3103.9179                   +0.0053
           3803.7959                   +0.0026
           4110.8769                   -0.0069
           4123.7345                   -0.0043
           4130.8748                   -0.0056
DO Cas     2636.7816                   +0.0041
           2664.8505                   +0.0017
           3728.8203                   +0.0006
           3795.9199                   +0.0029
           4095.8017                   +0.0010
XX Cep     2663.7526                   +0.0112
           4133.9311                   +0.0218
AT Peg     Z661.8136                   -0.0131
           3728.8093                   -0.0412
           4089.8270                   -0.0465
           4128.7925                   -0.0486
           4136.8149                   -0.0489



                  Table I, (cont.)


BW Vul     2350.7826                  +0.0016
           2356.8079                  -0.0044
           2678.8813                  +0.0018
           3002.9597                  +0.0026
           3012.8135                  +0.0054
           3060.6542                  -0.0016
           3724.8889                  -0.0054
           3729.9214                  +0.0011
           3755.8520                  -0.0026


times cited in SAC 51 (1979).

   The provisional ephemerides suggested by Margrave (1979b) for K0 Aql,
TV Cas, TW Cas, and AT Peg have been redetermined using the revised times with
the following results.
K0 Aql: Hel. JD (Min) = 2,441,887.4724 + 2.864055d E
TV Cas: "  = 2,441,595.3582 + 1.8125944d .E
TW Cas: "  = 2,442,008.3873 + 1.4283240d .E
AT Peg: "  = 2,440,407.4365 + 1.14611064d .E - 6.2110 x 10^{-9} .E^2

The mean residuals for these ephemerides are 0.0010d, 0.0008d, 0.0028d, and 0.0017d,
respectively. The quadratic ephemeris for AT Peg implies a continuous period
decrease since 1969 of 17.1 seconds per century.

  The author deeply regrets any confusion or inconvenience that the erroneous
timings have caused. He also expresses his sincere gratitude to C. R. Chambliss
and E. C. Olson for pointing out the systematic deviation of the RZ Cas eclipse
timings from this observatory.




                           THOMAS E. MARGRAVE


                           Blue Mountain Observatory
                           University of Montana
                           Missoula, Montana 59812
                           USA



References:
Chambliss, C. R. et al. 1979, IBVS No. 1679.
Margrave, T. E. et al. 1975, IBVS No. 1019.
             1978, IBVS No. 1478.
Margrave, T. E. and Mefford, J. W. 1975, IBVS No. 1051.
Margrave, T. E. 1979a, IBVS No. 1631.
         1979b, IBVS No. 1694.
         1979c, Publ. Astron. Soc. Pacific 91, 666. [BIBCODE 1979PASP...91..666M ]
Olson, E. C. 1980, IBVS No. 1840.
Rudnicki, K. 1979, SAC 51, p. 100.
Tunca, Z. 1978, IBVS No. 1386.