COMMISSION 27 OF THE I. A. U.
        INFORMATION BULLETIN ON VARIABLE STARS
                     NUMBER 560

                               Konkoly Observatory
                               Budapest
                               1971 June 9


            UBV PHOTOMETRY OF BM Cas

      The supergiant eclipsing binary BM Cassiopeiae
(P = 197.3d) is of considerable interest, especially since
Thiessen (1956) has suggested that one component is a
classical Cepheid (P = 27d).
      In the fall of 1967 fourteen UBV observations were
obtained which covered the rising branch of primary eclipse,
Because no further observations of BM Cas are planned at
this observatory, the results are presented here for others
to use. According to the IAU Program Notes for Eclipsing
Binaries, Numbers 9 and 18, respectively, Chao at Harvard
and Kalv at Tallinn have been observing BM Cas 
photoelectrically.
      The three-color observations, obtained with the Dyer
Observatory 24-inch reflector and a refrigerated 1P21 
photomultiplier, were made differentially with respect to the
comparison star BD +63d101. The differential magnitudes were
corrected for differential extinction and transformed 
differentially to the UBV system in the usual way. The results
are presented in Table I, where the first column lists the
heliocentric Julian date and the last three columns list
DeltaV, Delta(B-V), and Delta(U-B), respectively.



              Table I
     Differential UBV Magnitudes
      (BM Cas minus BD +63d101)
----------------------------------------
JD (hel.)  DeltaV  Delta(B-V) Delta(U-B)
2,439,000+
----------------------------------------
783.847    +0.885   +0.898   +0.598
   .858      .889     .899     .594
784.947      .839     .915     .567
785.780      .815     .902     .612
   .791      .815     .909     .603
791.826      .625     .923     .561
   .839      .623     .899     .557
797.608      .483     .858     .534
799.577      .452     .891     .521
800.816      .437     .849     .483
802.875      .453     .849     .471
803.841      .437     .856     .497
804.767      .432     .859     .493
807.911    +0.421   +0.878   +0.481
----------------------------------------




    The comparison star BD +63d101 was tied in to the
UBV system, the resulting magnitudes being y = 5.45m + 0.02m,
B-y = +0.18m + 0.01m, and U-B = +0.14m + 0.02m. This makes it
possible to convert the differential magnitudes in Table I
to actual magnitudes.


May 31, 1971


                         DOUGLAS S. HALL

                        Dyer Observatory
                      Vanderbilt University
                    Nashville, Tennessee 37203
                           U.S.A.



Reference:
Thiessen, G. 1956, Z. Astrophys. 39, 65. [BIBCODE 1956ZA.....39...65T ]