COMMISSION 27 OF THE I. A. U.
        INFORMATION BULLETIN ON VARIABLE STARS
                    Number 2043

                                 Konkoly Observatory
                                 Budapest
                                 1981 November 16

                                 HU ISSN 0374-0676





    PHOTOELECTRIC LIGHT CURVES OF CK BOOTIS (HD 128141)


    The system, which was discovered to be a binary of
WUMa type by Bond (1975), has been observed in two colours
with the 30 cm Maksutov telescope of the Ankara University
Observatory. Bond's comparison star, HD 128128, was adopted.
HD 128186 and BD +09d2919 were used as check stars.

     Two light curves obtained in 1977 and 1978 are presented
in Figs. 1 and 2, respectively. The phases were calculated from
the formula (Aslan, 1978):

     HJD 2442897.3759 + 0.3551501d E

     The light curve displays typical W UMa type features
with a scatter of individual observations that is more than
expected from observation errors alone; the mean rms error
of a single differential measure is about 0.015m in both
colours. The most important property of the light variation
is the interchanging depths of the eclipses. Such behavior
has been observed in AC Boo, AM Leo and TZ Boo. Hoffmann
(1978,1980) has recently discussed his observations of TZ
Boo in some detail.

     The minimum at phase 0.0, which will be called arbitrarily
the primary minimum, is seen to be the fainter one in Fig. 1,
but in the observations of Bond, it was the brighter. In 1978
observations in Fig. 2, the sense has reversed again.


     The primary minimum was fainter than the secondary in
1977 (Fig. 1) by 0.02m in v and 0.03m in b. In 1978 (Fig. 2) the
minima were almost equally deep, the secondary being slightly
deeper by about 0.015m in b, but not more than 0.01m in v.


                       [FIGURE 1]
                       [FIGURE 2]


    Comparing the 1977 and 1978 light curves, it is seen that
there was hardly any change in the brightness of the secondary
minimum but the primary minimum became brighter in 1978 by
about 0.03m in v and 0.04m in b, with a large scatter from
night to night. This presumably indicates that the source of
the changes is the eclipsing component during the primary
minimum.

    Another feature of the light curve is that the maximum
preceding the primary minimum is brighter than the maximum
following the primary minimum, the phasing being the same as
in Bond's light curve, save the interchange of the depths of
the eclipses. Maxima attained in 1977 and in 1978 light curves
were almost the same with the exception of 5th March 1978, on
which the system was decidedly brighter near the phase 0.75,
with no difference in the level of the minimum.

    Any change in b-v colour index over the period is less
than 0.01m. The observation, together with those in 1981 will
be given elsewhere.

     This work has been supported by TUBITAK (the Scientific
and Technical Research Council of Turkey).





                      Z. ASLAN, M. GOREN, E. DERMAN
                      Ankara University Observatory
                      A.U. Fen Fakultesi
                      Ankara, Turkey

References:
Aslan, Z. 1978, IBVS No. 1462
Bond, H.E. 1975, P.A.S.P. 87, 877 [BIBCODE 1975PASP...87..877B ]
Hoffmann, M. 1978, Astron. Astrophys. Suppl. 33, 63 [BIBCODE 1978A&AS...33...63H ]
Hoffmann, M. 1980, Astron. Astrophys. Suppl. 40, 263 [BIBCODE 1980A&AS...40..263H ]