COMMISSION 27 OF THE I.A.U.
               INFORMATION BULLETIN ON VARIABLE STARS
                            Number 1487

                                                      Konkoly Observatory
                                                      Budapest
                                                      1978 October 17


  A NEW EXTREME LIGHTCURVE OF THE W UMa SYSTEM TZ BOOTIS

Photometric observations by Binnendijk (1969), Carr (1971)
and Hoffmann (1978) revealed the very strong variations of the
lightcurve of TZ Bootis. This W UMa system should be classified
as W type, although the considerably deeper transit minima of
1967 and 1975 suggest the opposite. Such a behaviour is known
only for very few systems. In three subsequent nights in April
1978 the observations of TZ Bootis with the double beam photometer 
at the 106cm telescope of Hoher List Observatory could be
continued. The B measurements are shown in Figure 1 together
with the 1971 lightcurve for illustration. Now the variation at
the transit minimum reaches almost half the amplitude of the
lightcurve during the last years itself. It is larger than the
adopted luminosity of the secondary.
   The only reliable tool for the determination of minimum times
seems to be the incidence of the second and third contact at
occultation. From these phases an (O-C)-value of + 0d.012 has
been adopted (ephemeris by Binnendijk, 1969), suggesting an 
increase of the period since 1976. Possibly rapid changes in the
degree of contact are taking place. A publication of more details
and further observations are planned for the near future.


                            M. HOFFMANN

                      Observatorium Hoher List
                   der Universitats-Sternwarte Bonn
                         5568 Daun/Eifel



References:

Binnendijk, L., 1969, Astron. J. 74, 211 [BIBCODE 1969AJ.....74..211B ]
Carr, R.B., 1971, Publ. Goodsell Observatory 16
Hoffmann, M., 1978, Astron. Astrophys. Suppl. 33, 63 [BIBCODE 1978A&AS...33...63H ]


                       [FIGURE 1]

   Figure 1: B lightcurves of TZ Bootis. Small dots: 1978 observations,
   open circles: 1970 normal points.