COMMISSIONS 27 AND 42 OF THE IAU 
           INFORMATION BULLETIN ON VARIABLE STARS 
                        Number 3727 
 
                                              Konkoly Observatory 
                                              Budapest 
                                              13 May 1992 
 
                                              HU ISSN 0374 - 0676 
 
 
 
        1991 PHOTOMETRY OF THE W UMa-TYPE BINARY CK Boo 
 
 
  Variability of the W UMa-type eclipsing binary CK Boo was discovered by Bond ( 1975). 
Aslan and Derman (1986) observed photoelectrically and gave the improved ephemeris, 
 
          Min (I) = J.D.(hel.) 2442897.3759 + 0.3551501d x E 
 
  Demircan (1987) made BV photoelectric observations in April 1985, Pajdosz arid Zola 
(1988) observed CK Boo in BV system in 1988. 
  We have put the system in our program in order to determine accurate ephemeris 
and to study its short time-scale light variation and the change in its orbital period. 
Photoelectric observations of CK Boo in UBV and Stromgren's Hbeta(w), Hbeta(n) systems 
were made on six nights between April and May in 1991 at Xinlong Station of Beijing 
Observatory. We used HD 128128 as the comparison star which was adopted by Bond 
(1975). 
  The light curves in U, B, V, Hbeta(w) and Hbeta(n) are shown in Figure 1 and 3 respectively. 
The B-V and U-B colour indices are plotted in Figure 2. The light minimum times are 
listed in Table II which includes other determinations known to us. The O-C residuals of 
the minimum time were calculated using the elements given by Aslan and Derman ( 1986). 
The O-C curve was made using the data of minima times from 1975 to 1991 (see Figure 
4). It had been fitted well by a parabolic curve, indicating that the orbital period of CK 
Boo is increasing continuously by 0.149 s/century, and its orbital period was 
0.35520d in 1991. 
 
Table I. The amplitudes of the light curve 
and the average magnitude of colour index 
 
Filter    Average Amplitude   Colour Index   Average Magnitude 
 
U         0.30+/-0.02           U-B            -0.09+/-0.05 
          0.27+/-0.01           B-V            +0.02+/-0.04 
V         0.26+/-0.01 
Hbeta(w)  0.25+/-0.02            beta          -0.02+/-0.04 
Hbeta(n)  0.28+/-0.02 
 

                               [FIGURE 1]

               Figure 1   THE UBV LIGHT CURVES OF CK Boo
 
                               [FIGURE 2]

      Figure 2   THE COLOUR INDEXES OF (U-B) AND (B-V) FOR CK Boo

                               [FIGURE 3]

 Figure 3   THE beta INDEX CURVE, Hbeta(w) AND Hbeta(n) LIGHT CURVES OF CK Boo


             Table 2.  The minimum times of CK Boo 
 
JD(hel)             E       O-C    Ref. 
2440000.0+                (days) 
   2537.4330     1013.5   0.0170   (1) 
   2897.3759        0.0   0.0000   (2) 
   2898.4418        3.0   0.0004   (2) 
   3225.5334      924.0  -0.0012   (2) 
   3229.4409      935.0  -0.0003   (2) 
   3230.5069      938.0   0.0002   (2) 
   3341.3122     1250.0  -0.0013   (2) 
   3573.5846     1904.0   0.0029   (2) 
   3667.3400     2168.0  -0.0013   (2) 
   3670.3610     2167.5   0.0009   (2) 
   4753.3929     5226.0   0.0026   (3) 
   4756.4161     5234.5   0.0070   (3) 
   4790.3294     5330.0   0.0035   (3) 
   5054.5625     6074.0   0.0049   (3) 
   5057.5829     6082.5   0.0065   (3) 
   5132.3408     6293.0   0.0053   (3) 
   5140.3339     6315.5   0.0075   (3) 
   6183.4100     9252.5   0.0088   (4) 
   6183.4100     9252.5   0.0078   (4) 
   7290.4153    12369.5   0.0102   (5) 
   7290.4146    12369.5   0.0095   (5) 
 
   7291.4796    12372.5   0.0091   (5) 
   7292.3699    12375.0   0.0115   (5) 
   7298.4072    12392.0   0.0113   (5) 
   8362.0907    15387.0   0.0202   U* 
   8362.0913    15387.0   0.0208   B* 
   8362.0908    15387.0   0.0203   V* 
   8385.1797    15452.0   0.0244   U* 
   8385.1814    15d52.0   0.0261   B* 
   8385.1806    15452.0   0.0235   V* 
   8386.0668    15454.5   0.0237   U* 
   8386.0695    15454.5   0.0264   B* 
   8386.0664    15454.5   0.0233   V* 
   8386.2429    15455.0   0.0222   U* 
   8386.2434    15455.0   0.0227   B* 
   8386.2439    15455.0   0.0232   V* 
   8387.1319    15457.5   0.0273   U* 
   8387.1322    15457.5   0.0236   B* 
   8387.1321    15457.5   0.0235   V* 
   8388.1971    15480.5   0.0231   W* 
   8388.2002    15480.5   0.0262   N* 
 
(1) Bond (1975)                       (4) Demircan (1987) 
(2) Aslan (1978)                      (5) Pajdosz and Zola (1988) 
(3) Aslan and Derman (1986)            * this paper 


                                [FIGURE 4]

 Figure 4   The (O-C) values of minimum times for CK Boo

 
 The short time-scale light variations were analysed by auto-regression (AR) power 
spectral and Fourier method. There are no other significant short-term variations except 
the 4.3 hours period which is probably half the orbital period. 
 
 
 
 
      JIA GUISHAN             LIU XUEFU and HUANG HE 
      Beijing Planetarium     Beijing Normal University 
      Beijing, China          Beijing, China 
 
 
 
 
References: 
 
Aslan, Z.: 1978, I.B.V.S. No. 1462 
Aslan, Z., Derman, E.: 1986, Astron. Astrophys. Suppl. 66, 281  [BIBCODE 1986A&AS...66..281A ]
Bond, H.E.: 1975, Publ. Astr. Soc. Pacific 87, 877  [BIBCODE 1975PASP...87..877B ]
Demircan, O.: 1987, Astrophys. Space Sci. 135, 169  [BIBCODE 1987Ap&SS.135..169D ]
Pajdosz, G. and Zola, S.: 1988, I.B.V.S. No. 3251