COMMISSION 27 OF THE I.A.U.
              INFORMATION BULLETIN ON VARIABLE STARS
                           Number 1403

                                                     Konkoly Observatory
                                                     Budapest
                                                     1978 March 30


      PERIOD CHANGES OF THE BINARY SYSTEM RX CASSIOPEIAE

The investigation of period changes of the Beta Lyrae-type
eclipsing binary RX Cas was based on 25 epochs of primary and 
secondary minima listed in Table 1. The (O-C)_1 values were calculated
according to Martynov's (1950) elements:

         Min. = J.D. 241 6250.731+32.3165 * E                (1)

   The last times of minima indicate that the period appears to
be increasing. On the basis of all available material new elements
with second order term were calculated. A least squares solution
gives:

         Min. = J.D. 2916251.10+32.3100*E+1.39*10^-5*E*E   (2)
                           +-13     +-6    +-6

The (O-C)_2 values in Table 1 were calculated according to above
mentioned elements. As it is seen in the Figure a parabolic-like
fit is a good approximation of changes of period. From the elements
(2) the following results were obtained:

                DeltaP = 2.40 sec  epoch^-1
              DeltaP/P = 0.86*10^-6
             d ln p/dt = 0.97*10^-5


   Thus, RX Cas is one of the binary systems with extremely large
changes of period. This is with a good agreement with Paczynski's
(1971) suggestion that all binaries with Beta Lyrae - type light
curves and periods longer than 10 days may be suspected to be in a
phase of rapid evolution connected with rapid transfer of matter.
Further photoelectric and spectral observations of this interesting
system would be very desirable.


                          J.M. KREINER

                   Silesian University, Katowice
                      Institute of Physics
                    Astronomical Laboratory



                         Table 1

J.D. hel.         Epoch    (O-C)_1   (O-C)_2   Source

2416250.9            0     +0.169     -0.200     1
   7511.19          39     +0.116     -0.021     1
   8803.780         79     +0.046     +0.103     1
2422907.75         206     -0.180     +0.200     2
   3198.31         215     -0.469     -0.083     1
   4943.60         269     -0.270     +0.104     1
   5492.93         286     -0.320     +0.033     1
   6947.213        331     -0.280     -0.020     1
   7464.325        347     -0.232     -0.019     1
   7916.931        361     -0.057     +0.110     1
   8434.108        377     +0.057     +0.162     1
   8886.456        391     -0.027     +0.021     1
   9338.987        405     +0.074     +0.057     1
   9662.334        415     +0.256     +0.190     1
   9855.735        421     -0.243     -0.339     3
2430050.037        427     +0.161     +0.033     1
   0534.971        442     +0.347     +0.135     1
   0890.075        453     -0.031     -0.307     1
   1116.6          460     +0.279     -0.041     1
   3540.85         535     +0.792     -0.079     4
   4154.90         554     +0.828     -0.206     4
2442706.5 sec      818.5   +4.714     +0.353     5
   2706.53 sec     818.5   +4.744     +0.383     6
   2883.69         824     +4.163     -0.288     6
   2883.7          824     +4.173     -0.278     5

1. Martynov (1950), 2. Gaposchkin (1941), 3. Gaposchkin (1953),
4. Domke, Pohl (1953), 5. Mallama et al. (1977), 6. Rhombs (1978).


References:

Domke, K., Pohl, E. 1953, A.N. 281, 113 [BIBCODE 1953AN....281..113D ]
Gaposchkin, S. 1941, Ap. J. 100, 230 [BIBCODE 1944ApJ...100..230G ]
Gaposchkin, S. 1953, Harvard Ann. 113, 69 [BIBCODE 1953AnHar.113...67G ]
Mallama, A.D., Skillman, D.R., Pinto, P.A., Krobusek, B.A. 1977,
      I.B.V.S. No. 1249
Martynov, D.Ya. 1950, Engelhard Bull. No. 27
Paczynski, B. 1971, A. Rev. Astr. Astrophys. 9, 183 [BIBCODE 1971ARA&A...9..183P ]
Rhombs, C.G. 1978, Private communication


                        [FIGURE 1]