COMMISSION 27 OF THE I. A. U.
                INFORMATION BULLETIN ON VARIABLE STARS
                             Number 2456

                                                 Konkoly Observatory
                                                 Budapest
                                                 2 January 1984

                                                 HU ISSN  0374-0676




                 CO Aur - DOUBLE MODE CHARACTER CONFIRMED



  By inspecting some 880 plates of the Sonneberg Sky Patrol taken from
1928-1983 we were able to find long time stability of the light curve 
parameters. One of us (B.F.) estimated the brightness by using the conventional
Argelander method and improved the first period given by Mantegazza and
Antonello (I.B.V.S. No. 2411, 1983). All bright observations were chosen
and the improved period of 1.783003d was obtained by conventional (O-C) 
calculation. After this, normal Fourier analysis of the original observations
was executed. For several reasons the data were subdivided into three time
sets. The first set contains the early observations (JD 2425500 to 2432000),
the second one the in-between (JD 2432000 to 2439000) data and the
third one the data from JD 2438000 to 2445000. All three sets were analysed
independently. A clear peak was found at 0.56805 cpd (P: 1.78301d). The
Fourier analysis for the first frequency was executed in the restricted
frequency range of 0.55 cpd to 0.57 cpd with frequency steps of 0.00001 cpd.





                              Table
Set   JD         Number    First component             Second component
                 of        f_l(cpd)   A_1(mag)   f_2(cpd)   A_2(mag)
                 observ.
I     2425500-   277       0.560865      0.17    0.70039     0.03
      2431840
II    2432280-   267       0.56085       0.20    0.70040     0.05
      2438000
III   2438620-   340       0.56085       0.20    0.70042     0.05
      2445400



After least square sine-fitting and prewhitening the data were again Fourier-
analysed (frequency range 0.4...0.8 cpd, step width 0.00005 cpd): In data
sets II and III the highest feature is then at 0.7004 cpd (P=1.4278d). In the
first data set the feature at this frequency is indicated just above the noise
level. One reason may be the inhomogeneity of the material of the first set.
Some preliminary characteristics for the data derived from the Fourier spectra
are given in the Table above. Further details will be published later.





              B. FUHRMANN, R.H. SCHULT

            Sternwarte Sonneberg
            Zentralinstitut fur Astrophysik
            der Akademie der Wissenschaften
            der DDR