COMMISSION 27 OF THE I. A. U.
        INFORMATION BULLETIN ON VARIABLE STARS
                    Number 1980

                                   Konkoly Observatory
                                   Budapest
                                   1981 June 19

                                   HU ISSN 0374-0676



    OBSERVATIONS OF TZ Boo, BL Leo, AND V524 Mon



    In February 1981 photoelectric observations of several
eclipsing binaries have been made with the 1.06m telescope
of Hoher List Observatory and its double beam photometer.
Among them are:
1) TZ Boo. A complete new light curve could be obtained.
The magnitudes at the four main phases were
Phase 0.00       B   11.49m     V 10.79m
      0.25           11.11        10.41
      0.50           11.47        10.77
      0.75           11.14        10.46

A minimum time has been determined

    JD hel. 2444650.5625        Ep. 16885.5    O-C -0.015d

according to the light elements (Hoffmann, 1980a)

    JD hel. min. I = 2439632.8418 + 0.2971620d E

The tendency of the O-C's noticed in 1980 (Hoffmann, 1980b)
has continued and increased to -0.05p. So it is suggested
that the period of TZ Boo has in fact become shorter.
    The light curve shows an almost round shaped, slightly
declining minimum at phase 0.5 when there should be the flat
and sharply limited occultation minimum. Also a brighter
maximum at phase 0.25 is not usual for TZ Boo, although it
has been observed previously, for instance in 1975.
2) BL Leo. A minimum time has been observed, but there are
only few measurements defining the rising branch after the
minimum. The minimum was at

    JD hel. 2444648.615      Ep. 24821.5     O-C -0.009d
So the light elements
    JD hel. min. I = 2437650.654 + 0.2819318d E

given by Meinunger and Wenzel (1968) seem to be generally
confirmed.
3) V524 Mon. A complete light curve has been measured in B.
Comparison star has been a 10th magnitude star 24mm above
the variable in the chart by Wachmann (1966). The following
minima times have been determined:

    JD hel. 2444648.295     Ep. 35970.5     O-C +0.003d
            2444648.434         35971.0          0.000
These data are obviously still well consistent with the light
elements by Wachmann
    
   JD hel. min. I = 2434446.442 + 0.28361714d E

The accuracy of the individual measurements has been lowered
by a strongly moonlit sky. Therefore only normal points are       
given in Fig. 1 where the light curve is shown. There are no

                       [FIGURE 1]

   Fig. 1   B light curve of V524 Mon (normal points).


detectable brightness differences between the maxima as well
as between the minima within the limits of accuracy. The
minimum at phase 0.5 seems to be slightly wider. So that
minimum may be of occultation type.





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





References:

Hoffmann, M., 1980a, Astron. Astrophys. Suppl. Ser. 40, 263 [BIBCODE 1980A&AS...40..263H ]
Hoffmann, M., 1980b, Inf. Bull. Variable Stars No. 1877
Meinunger, L., Wenzel, W., 1968, Veroff. Sternw. Sonneberg
          7, H. 4, 389 [BIBCODE 1968VeSon...7..385M ]
Wachmann, A. A., 1966, Abh. Hamburg-Bergedorf 7, 341