COMMISSION 27 OF THE I. A. U.
             INFORMATION BULLETIN ON VARIABLE STARS
                          Number 3410

                                           Konkoly Observatory
                                           Budapest
                                           28 December 1989

                                           HU ISSN 0374 - 0676


                      THE PERIOD OF KO Aur

   KO Aur (BD+48d1340) was discovered by Weber (1963) and this star was
reported by Berthold (1978) to be an eclipsing binary with a period of
1.31793028 days and with 0.75m and 0.70m deep primary and secondary eclipses
respectively. The ephemeris given by Berthold is as follows:
         Min. (hel.)= JD.2436607.472+1.31793028d*E
   From December 1988 to March 1989 this star was observed photoelectrically 
in UBV colours at Xinglong station, Beijing observatory with the 60 cm
reflector.
   The stars BD+48d1342 and BD+48d1344 were used as the comparison and
the check star respectively.
   The light curves with 614 UBV photoelectric observations were obtained
on nine nights and six times of minima were determined by Kwee and Van
Woerden's (1956) method. The results reveal that during the interval of our
observation some minima times predicted according to the ephemeris given by
Berthold (1978) were detected and some were not. It is interesting to note
that the minima times detected just coincide with those minima times 
predicted according to an ephemeris with a triple of the old period given by
Berthold (1978).
   17 times of minima are listed in Table I, six of which are given by us
and 11 of which were given by Berthold. Six times of minima are excluded
from the moments given by Berthold, because the O-C residual of those
minima times is over 0.5d.
   The ephemeris deduced by the weighted least squares method is as
follows:

      JD.Hel(Min I)=2447512.0677+3.9538047d*E
                           +/-23        28


   The light curves in BV colours are given in Figure 1. The O-C diagram
of minima times is shown in Figure 2. The O-C residuals of minima times
show that the period for this binary seems to be constant over the time 
interval covered.

   It is interesting to note that the binary system may be an RS CVn-type


                            [FIGURE 1]

        Fig. 1. The light curves of KO Aur in BV colours

                            [FIGURE 2]

        Fig. 2. The O-C diagram of times of minima for KO Aur


             Table I. Times of minima of KO Aur

JD.(hel)           E     O-C       weight   observer
 2400000+                (days)
36607.4500     -2758.0.  -0.0244    1         Berthold
37639.4590     -2497.0    0.0416    1         "
37730.3560     -2474.0    0.0011    1         "
38406.4780     -2303.0    0.0225    1         "
38495.3800     -2280.5   -0.0361    1         "
38651.6100     -2241.0    0.0186    1         "
38849.3110     -2191.0    0.0294    1         "
39070.6270     -2135.0   -0.0677    1         "
40205.4250     -1848.0   -0.0116    1         "
42866.3680     -1175.0    0.0208    1         "
42870.3230     -1174.0    0.0220    1         "
47506.1378        -1.5    0.0008   10        Zhang et al.
47510.0894        -0.5   -0.0014   10        "
47512.0687         0.0    0.0010   10        "
47595.0973        21.0   -0.0003   10        "
47597.0717        21.5   -0.0028   10        "
47599.0522        22.0    0.0008   10        "

eclipsing binary with a distortion wave outside the eclipses of the light
curve but, in order to reveal other RS CVn characteristics, spectroscopic
observations of this system are necessary.



                         ZHANG RONG-XIAN, ZHANG JI-TONG,
                         ZHAI DI-SHENG


                         Beijing Astronomical Observatory
                         Academia Sinica
                         Beijing 100080
                         China



References:
Berthold, T.: 1978, Mitteilungen der Bruno-H.-Burgel-Sternwarte Hartha,
        Heft 12.
Kwee, K.K. and Van Woerden, H.: 1956, Bull. Astron. Inst. Netherl. 12,
        327. [BIBCODE 1956BAN....12..327K ]
Weber, R.: 1963, IBVS, No. 21.