COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                     Number 1976

                                  Konkoly Observatory
                                  Budapest
                                  1981 June 19

                                  HU ISSN 0374-0676


       PHOTOMETRIC OBSERVATIONS OF V523 Cas


    V523 Cas is an eclipsing binary of W UMa type with one,
of the shortest known periods (0.2337d). Discovered by Weber
(1957), photoelectric observations and analyses have been
given by Lavrov and Zhukov (1975, 1976) and Bradstreet (1981).
    In November 1979, V523 Cas has been observed during
four nights with the 1.06m telescope of Hoher List Observatory 
and its double beam photometer. The light curves in B
and V are shown in Figs. 1 and 2. An independent analysis
of these data has been carried out, but as the results generally 
agree well with those obtained by Bradstreet, only a
few remarks seem to be necessary.
    Minima times have been determined:
JD hel.2444191.3291   Min. II
       2444194.4828   Min.I
       2444195.5363   Min. II
       2444200.3262   Min.I

A combination of the minima times determined by Lavrov and
Zhukov (1976), Busch (1974), Bradstreet (1981) and those 
listed above indicate an increase of the period to 0.2336908d
since JD 2441300.
    At the maxima and at primary minimum small night to
night brightness changes have have been noticed, but they
had no detectable effect on the light curve analysis. It is
interesting to note that an analysis of the data by means of
the Russell-Merrill method reproduced essentially the 
elements found by Lavrov and Zhukov. So the light curve is 
apparently quite stable. Because of the well known shortcomings
of this method, applied to W UMa binaries, their findings
have to be translated to the contact model, however. Somewhat 
critical seems to be the question if V523 Cas has complete 

                       [FIGURE 1]

 Fig. 1   B light curve of V523 Cas relative to BD+49d 151

                       [FIGURE 2]

           Fig. 2   V light curve of V523 Cas 


or partial eclipses. There is a rivalty of the results
by the Russell-Merrill type analysis which yields only a 
definite complete eclipse solution (and - even more important -
of the data in fig. 4 in the paper by Lavrov and Zhukov
(1976) which shows a flat bottom of the primary minimum)
versus the theoretical light curve solution by Bradstreet,
who obtained incomplete eclipses. The observations reported
here do not show a constant part in the occultation minimum,
but the eclipses are probably almost tangential.
    V523 Cas exhibits two minor complications which are
very similar to respective ones in CC Comae (Rucinski, 1976).
1) The second maximum is slightly brighter than the first
maximum: the B_1 rectification coefficient in the classical
second order Fourier expansion of maximum light is -0.0072.
For longer period W type systems usually a slight brightness
excess of the maximum following the occultation can be found.
2) The colour at min. II becomes redder than expected.                       
It is suggested that the present assumptions on the brightness 
and temperature distributions on the components are not
quite sufficient yet to explain these phenomena in the coolest 
contact binaries.




                      M. HOFFMANN

                  Observatorium Hoher List
                  5568 Daun / Eifel, BRD





References:
Bradstreet, D. H., 1981, Astron. J. 86, 98 [BIBCODE 1981AJ.....86...98B ]
Busch, H., 1974, Mitt. Hartha H. 7, 12
Lavrov, M. I., Zhukov, G. V., 1975, Astron. Circ. No. 873, 1 [BIBCODE 1975ATsir.873....1L ]
Lavrov, M. I., Zhukov, G. V., 1976, Publ. Kazan University
          Observatory 42, 46
Rucinski, S. M., 1976, Publ. Astron. Soc. Pacific 88, 777 [BIBCODE 1976PASP...88..777R ]
Weber, R., 1957, Bull. Soc. Astron. Fr. 71, 36