COMMISSION 27 OF THE I. A. U.
           INFORMATION BULLETIN ON VARIABLE STARS
                        Number 3641

                                           Konkoly Observatory
                                           Budapest
                                           17 July 1991

                                           HU ISSN 0374 - 0676


     THE TOTALITY IN A PRIMARY MINIMUM OF RZ CASSIOPEIAE


    RZ Cas (HD17138) is an eclipsing binary system (P = 1.195d) and
has shown irregular period changes (e.g., Herczeg & Frieboes-Conde
1974; Nowak & Piotrowski 1982). The system is bright enough (m_v=
6.18m at light maxima), so many photometric observations, mostly by
rather small telescopes, have been made, which mainly concern
with the timing of primary minima of the system.

    There are also some reports on the type of the primary
minimum, i.e., whether it is a total eclipse or partial one. Some
observations show totality, but the others do not. For example,
those by Huffer and Kopal (1951), Huffer (1955), Chambliss (1976),
Surkova (1988), etc. show partial eclipses. On the contrary, those
by Szafraniec (1960), Burke and Rolland (1966), Margrave et al.
(1975), Arganbright et al. (1988), and Hegedus (1989), etc. seemed
to show total ones. Even among the observations which show
totality, the duration of totality reported differs from one
another, i.e., from 9 to 22 minutes, and moreover there is a report
that the duration of totality depends on the colour (Hegedus 1989).

    The spectral types of the components have been assigned to
A2V and G5IV (Chambliss 1976). The colour changes during the
primary eclipse are not so large: the colour index at the primary
minimum is about B - V = 0.23m, which corresponds to late A to early
F, never to G. This is one reason why the primary minimum is
considered to be partial, not total (e.g., Chambliss 1976).
Accordingly, some observers whose observations show total primary
minima are doubtful of the totality (Arganbright et al. 1988).

    On December 21 in 1989 we observed the system photoelectrically 
with the 91-cm telescope equipped with the multi-channel
polarimetric photometer at the Dodaira Station of the National
Astronomical Observatory of Japan. This photometer of eight
channels makes the simultaneous photometry possible. The effective
wavelength of each channel is 360 nm (ch.1), 420 nm (ch.2), 460 nm
(ch.3), 535 nm (ch.4), 650 nm (ch.5), 695 nm (ch.6), 760 nm (ch.7)
and 880 nm (ch.8), respectively (Kikuchi 1989). The other details
of this polarimetric photometer are described in Kikuchi (1988).


                           [FIGURE 1]

 Figure 1. Light curves of a primary eclipse of RZ Cas. The circles
          represent averaged data usually from three points. The
          abscissa is Universal Time.

                           [FIGURE 2]

 Figure 2. Enlarged light curves near the bottom of the minima of RZ Cas.
          The circles are individual observations.


    On that night we observed a primary minimum with flat bottom
showing totality. The comparison star was BD+69d 171 (HD16393) and
the check star HR791 (HD16769). The differential light curves of
the primary minimum at channels 1 through 7 are shown in figure 1
and the enlarged ones around the bottom in figure 2. As can be
seen in these figures, the duration of the totality are the same
with one another, which is estimated to be 14 minutes irrespective
of the colour, corresponding to 0.0081p. The central time of the
minimum has been estimated, after the heliocentric correction, to
be HJD 2447882.0971.

    Olson (1982) argued that there have been instabilities in the
light curves of primary eclipse of RZ Cas, and that the shapes of
the primary eclipse vary between partial-type and total-type. We
have observed several primary minima of the system also with the
45-cm telescope of Fukushima University in the period covering the
above date and found that they were usually total eclipses, the
result of which will be published elsewhere.


         Y. Nakamura, S. Narusawa and M. Kamada*
            Department of Science Education
            Faculty of Education, Fukushima University
            Fukushima, 960-12 JAPAN
          *)Furukawa Dai-4 Elementary School
            Furukawa, Miyagi, 989-61 JAPAN

REFERENCES

Arganbright, D.V., Osborn, W., Hall, D.S.: 1988, IBVS, No. 3224,
Burke, E.W., Rolland, W.W.: 1966, AJ, 71, 38, [BIBCODE 1966AJ.....71...38B ]
Chambliss, C.R.: 1976, PASP, 88, 22. [BIBCODE 1976PASP...88...22C ]
Hegedus, T.: 1989, IBVS, No. 3381.
Herczeg, T., Frieboes-Conde, H.: 1974, A&A, 30, 259, [BIBCODE 1974A&A....30..259H ]
Huffer, C.M.: 1955, ApJ, 121, 677, [BIBCODE 1955ApJ...121..677H ]
Huffer, C.M., Kopal, Z.: 1951, ApJ, 114, 297, [BIBCODE 1951ApJ...114..297H ]
Kikuchi, S.: 1988, Tokyo Astron, Bull., 2nd ser., No. 281,
Kikuchi, S.: 1989, Private Communication
Margrave, T.E., Lukes, M.A., Doolittle, J.H., Evenskaas, R.S., MacDonald,
       J.W. and Murray, N.D.: 1975, IBVS, No. 1019.
Nowak, A., Piotrowski, S.L.: 1982, Acta Astr., 32, 401, [BIBCODE 1982AcA....32..401N ]
Olson, E.C,: 1982, ApJ, 259, 702. [BIBCODE 1982ApJ...259..702O ]
Surkova, L.P.: 1988, Astr, Tsirk., No, 1533. [BIBCODE 1988ATsir1533...17S ]
Szafraniec, R.: 1960, Acta Astr., 10, 99. [BIBCODE 1960AcA....10...99S ]