COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                     Number 1619

                                    Konkoly Observatory
                                    Budapest
                                    1979 June 7

          PHOTOELECTRIC MINIMA OF RZ CASSIOPEIAE


	During the past season three times of minimum light of
RZ Cas were obtained by us. The first two were observed at the
Kutztown State College Observatory using the 46-cm telescope
equipped with an EMI 6256 SA photomultiplier while the third was
observed at Kitt Peak National Observatory using the 0.4 meter
telescope no.4 equipped with an RCA 1P21 photomultiplier. All
observations were made in B and V light.

	The times of minimum light are as follows:
Hel. JD             E          O-C
2443832.5929        11677    0.0000d
    844.5449        11687   -0.0005
    875.6224        11713   +0.0006

	The epoch and O-C values have been calculated from the
ephemeris given by Herczeg and Friboes-Conde (1974):
      JD Hel. Min. I = 2429875.6902+ 1.1952473d E.
	As noted by Barlow and Scarfe (1978) the ephemeris given
by Chambliss (1976) no longer predicts accurate times of minimum
light for RZ Cas. Thus it appears that its period has recently
undergone a change.
The Figure shows a plot of all photoelectric times of
minimum light of RZ Cas obtained since the investigation by Chambliss 
and published in the IBVS. The times of minimum light given
in that investigation are also included. The various observations
appear to be internally consistent except for those of Margrave
et al. (1975, 1978), which appear to be about 0.0045d too early.

                          [FIGURE 1]

These have been shifted by this amount and are indicated by crosses
rather than circles on the figure.
      The residuals and epoch number values have been calculated
using the ephemeris of Herczeg and Friboes-Conde. It appears that
an abrupt change of period occurred at about E = 10800, i. e.,
at the beginning of 1976. the period of RZ Cas is now about 0.5s
shorter than it was prior to this time.
      We wish to thank Dr. Colin Scarfe for the information
which he provided us on this system.


                             C. R. CHAMBLISS
                             J. J. BUTZ
                             E. L. SIMPSON

                             Kutztown State College
                             Kutztown, Penna.
                             USA 19530


References:

Barlow, D. J., and Scarfe, C. D., 1978, IBVS no. 1379
Chambliss, C. R. 1976, Pub. Astron. Soc. Pacific 88, 22 [BIBCODE 1976PASP...88...22C ]
Herczeg, T., and Friboes-Conde, H. 1974, Astron. and Astrophys.
         30, 259 [BIBCODE 1974A&A....30..259H ]
Margrave, T. E. et al. 1975, IBVS no. 1019
---------------  1978, IBVS no. 1478