COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                     Number 1877

                                   Konkoly Observatory
                                   Budapest
                                   1980 December 5

                                   HU ISSN 0374-0676



             TZ BOOTIS' 1980 LIGHT CURVE



The W UMa system TZ Bootis is one of the most observed eclipsing
binaries during the last decade. It could be shown that this
star has an extraordinary variable light curve even for W type
W UMa systems. Observations up to the middle of 1979 show repetitive 
interchanges of the minima depths with a period of about
3.5 years (Hoffmann, 1978, 1980). Just because of the frequent
measurements of the last years a dense patrol of the subsequent
light curve behaviour is of importance. Only then the development
and nature of the 3.5y period can be revealed. For that reason
further measurements of TZ Boo have been made on November 22,
1979, and May 12 and 13, 1980. They have been carried out in
B and V with the 106cm Cassegrain telescope of Hoher List Observatory 
and a two channel photometer. Period, phase and geographic 
position permitted the measurement of the two different
minima depths in November, although TZ Boo is then in conjunction 
with the sun at a separation of only 60^o. The occultation
minimum was then 0.06m fainter (B) than the transit minimum.
In May, a complete light curve could be obtained (Figures 1
and 2). This light curve has a quite regular appearance with
only a small O'Connell-effect. Smaller "complications" are
visible at several phases, for instance the sloped transit minimum. 
The amplitude of the light curve is moderately small
(0.38m; 1978: 0.51m, 1979: 0.34m (B)). The regularity of the light
curve is also demonstrated by the coefficients of the Fourier
series of the outside eclipse measurements:

    B l = 0.897 - 0.012 cos phi - 0.097 cos 2phi
             + 0.006 sin phi - 0.007 sin 2 phi
    V l = 0.913 + 0.006 cos phi - 0.093 cos 2 phi
             - 0.002 sin phi - 0.005 sin 2 phi

                       [FIGURE 1]

 Figure 1. May 1980 light curve of TZ Boo. Colour B.

                       [FIGURE 2]

 Figure 2. May 1980 light curve of TZ Boo. Colour V.

The sine coefficients are obviously small as well as the first
cosine term, the latter indicating a small reflection effect.
Minima times of TZ Bootis have been determined:

    Transit     JD 2444372.5710
    Occultation JD 2444372.4211

With the mean period of the last decade, P=0.2971620d, these

minima are 0.005d early. If this means a spurious period fluctuation 
can only be decided by subsequent observations. The
difference of the minima depths in May 1980 is only 0.01m, the
occultation being fainter. This means that TZ Boo is already on
the way again to deeper transit minima. There is no difference
in B-V at the minima, but the maximum following occultation is
markedly bluer than the other one. A temperature difference of
the "side" hemispheres can be claimed therefore. The reductions
have partly been carried out with a calculator granted by the
Deutsche Forschungsgemeinschaft (Schm 167/12). This shall be
gratefully acknowledged.






                        M. HOFFMANN
                    Observatorium Hoher List
                    5568 Daun / Eifel, BRD



References:
Hoffmann, M., 1978, I.B.V.S., No. 1487
Hoffmann, M., 1980, Astron.Astrophys.Suppl.Ser. 40, 263 [BIBCODE 1980A&AS...40..263H ]