COMMISSION 27 OF THE I.A.U.
                 INFORMATION BULLETIN ON VARIABLE STARS
                             Number 3289

                                                         Konkoly Observatory
                                                         Budapest
                                                         8 February 1989

                                                         HU ISSN 0374 - 0676


      ON THE SECONDARY MINIMUM OF THE ECLIPSING BINARY ZZ UMa

ZZ UMa was discovered as an eclipsing binary by Kippenhahn (Geyer et al.,
1955). The photographic light curve (Doppner, 1962) is of Algol type with the
shallow secondary minimum of uncertain depth. The results of the first photoelectric 
observations of ZZ UMa in two colours were published by Lavrova and
Lavrov (1988). According to the light curves obtained by them, the reflection 
and ellipticity effects are small. Due to the lack of measurements of
the secondary eclipse the photometric orbital elements were derived from the
primary minima only.
   The present paper reports 144 photoelectric U, B, V observations of ZZ UMa
in each colour at the orbital phases 0.45- 0.56. The measurements were made on
the night of March 16/17, 1988, using the 48 cm Cassegrain reflector of
Abastumani Observatory. Typical standard deviation of one observation, as
deduced from the maxima, is 0.018m, 0.014m, 0.009m in U, B, V respectively.
The normal points are presented in Figure 1. The magnitude differences are
given with respect to BD +62d1138. They are averages of four observations,
close in time. For calculations of the phases the light elements given by
Doppner (1962) were used.
   The orbital elements of the system have been derived using the method and
programs of Lavrov (1971, 1976). The solutions could be obtained only for a
total occultation in the secondary minimum.
   The final results and their probable errors are listed in Table I. The
subscript 1 denotes the hot primary component and the subscript 2 - the
cooler component. Only for V curves cos^2 i=0 and i=90. The elements for this
curve at i=90deg are listed in column headed V'. When our results are compared
with those published by Lavrova and Lavrov (1988), a good agreement is
found for all parameters with the exception of L_1. Our p.e. for L_1 is
considerably smaller than the previous one.
   Thus the new values of L_1 are more reliable. The values of the amplitudes
of the secondary minima A_2 are listed in the last line of Table I.


            Table I: The orbital elements of ZZ UMa

X_1             U             B              V              V'
(adopted)      0.75          0.75           0.60           0.60

k          0.693+-0.031   0.710+-0.011    0.700+-0.042     0.754+-0.015
r_1        0.162+-0.010   0.149+-0.004    0.160+-0.011     0.155+-0.005
r_2        0.112+-0.005   0.106+-0.002    0.112+-0.004     0.117+-0.002
L_2        0.796+-0.004   0.756+-0.002    0.741+-0.007     0.743+-0.002
cos^2 i        0             0          0.0020+-0.0021     0(adopted)
i             90 deg         90 deg        87.5 deg        90 deg
A_2            0.25m         0.30m           0.33m

   The spectral class of the secondary star is about G6-G8. Determination of
the epochs of mid-eclipse were made for all colours using Lavrov's (1976) 
program: J.D. hel. 2447237 + 0.3990d +- 0.0009d (in U), 0.3992d +- 0.0004d (in B),
0.3999d +- 0.0004d (in V).


                            [FIGURE 1]



        E.B. JANIASHVILI                           M.I. LAVROV

Abastumani Astrophysical Observatory             Kazan University
              USSR                            Department of Astronomy
                                                       USSR



References:

Doppner, M., 1962, Mitt. Verand. Sterne No. 630-631.
Geyer, E., Kippenhahn, R., Strohmeier, W., 1955, Kleine Veroff. Bamberg, No. 9.
Lavrov, M.I., 1971, Soviet Astron. J., 48, 951. [BIBCODE 1971AZh....48..951L ]
Lavrov, M.I., 1976, Variable Stars, Suppl. 2, No. 11, 349. [BIBCODE 1976PZP.....2..349L ]
Lavrova, N.V., Lavrov, M.I. 1988, Astron. Circ., No. 1529, 11. [BIBCODE 1988ATsir1529...11L ]