COMMISSION 27 OF THE I.A.U.
                 INFORMATION BULLETIN ON VARIABLE STARS
                             Number 3251

                                                         Konkoly Observatory
                                                         Budapest
                                                         17 October 1988

                                                         HU ISSN 0374 - 0676


                      NEW ELEMENTS OF CK Boo

The star CK Boo (HD 128141, BD +9d2916) is a W UMa-type eclipsing binary
discovered by Bond (1975). Its light curve varies form night to night. Aslan
and Derman (1986) suggested these long-term changes to be due to a starspot
cycle with a period of about 7 years.
   New photoelectric observations were obtained during May 1988 at Mt. Suhora
Observatory (1000 m above sea level, phi=+49d35', lambda=-1h20m22s) of the
Pedagogical University (Cracow) using the 60 cm Cassegrain telescope equipped
with a one-channel photometer. An uncooled EMI 9865B photomultiplier as well
as blue and yellow filters close to UBV Johnson-Morgan system were used. The
data logging was controlled automatically by a Commodore-64 microcomputer.
   The observations allowed us to determine the following times of minima by
parabolic fitting:


JDhel                   Filter   Minimum type

2447290.4153 +/- 0.0007     V         II
  47290.4146 +/- 0.0007     B         II
  47291.4796 +/- 0.0003     V         II
  47292.3699 +/- 0.0005     V          I
  47298.4072 +/- 0.0002     V          I

   Adding these times of minima to those available in the literature (see e.g.
Aslan and Derman 1986, Demircan 1987) we could improve the elements of the
system. The new elements are as follows:

       JDhel(min) = 2446183.5876 + 0.35515102d E
                            +/-1         +/-2

   The O-C residuals calculated using the above elements are plotted in
Figure 1.
   The new elements are more precise than those given by Aslan (1978) (see
O-C's in Figure 2 according to Aslan's elements).
   A complete discussion and light curve analysis of  the system will be
published soon.

                        [FIGURE 1]
                        [FIGURE 2]


   A part of this work was supported by a grant from Polish Ministry of
Education (RR I-11).


     G. PAJDOSZ                 S. ZOLA

 Institute of Physics     Astronomical Observatory
Pedagogical University    Jagiellonian University
   Cracow, Poland            Cracow, Poland



References:

Bond, H.E., 1975, P.A.S.P. 87, 877. [BIBCODE 1975PASP...87..877B ]
Aslan, Z., 1978, I.B.V.S. No. 1462.
Aslan, Z., and Derman, E., 1986, A.Ap. Suppl. Ser. 66, 281. [BIBCODE 1986A&AS...66..281A ]
Demircan, O., 1987, Ap. Sp. Sci. 135, 169. [BIBCODE 1987Ap&SS.135..169D ]