COMMISSION 27 OF THE I.A.U.
          INFORMATION BULLETIN ON VARIABLE STARS
                        NUMBER 95

                                        Konkoly Observatory
                                        Budapest
                                        14 May 1965


                          CT TAURI

   CT Tau is considered as belonging to the RW Aur type of
variables. But this is inconsistent with the periodicity of
its light variation, suspected from photographic observations
obtained at the Tashkent Astronomical Observatory. To clear
up the question, the star has been observed photoelectrically
at the Crimean Astrophysical Observatory during some nights
in December 1964 and January 1965.

   The periodicity was confirmed and the following minima
were observed:

           J.D. hel.   2438755.384
                           763.392
                           785.397

   The very small amplitude of the colour variations
excludes the possibility that pulsations are the cause of
the light variations of CT Tau. It seems reasonable to
conclude that the star is of W UMa type with the elements:

           Min. hel. = 2434310.315 + 0d.6668276E

having nearly equal minima, the limits of the light variations 
being 10.34-11.21 in V. The photographic observations
are also in good agreement with these elements.

   Determination of the luminosity and spectral type of
CT Tau is very important. Mean values of its colour indices
are: B-V = + 0.14, U-B = - 0.49. The colour excess, E_{B-V},
is about 0.4. Assuming the visual absorption in this direction 
to be about 1m.2 per kps, we obtain for CT Tau m-M~10
and M~0. The value of Q = -0.59 corresponds to spectral
class B3 in good agreement with N. B. Kalandadze's result
/Abastumany Bull. N. 31/. Other determinations of the
spectral class were given by G. H. Herbig: B5:n /Trans.
I.A.U., 8, 805/ and B2n /Ap.J., 131, 632/. It is probable
that the luminosity of the star is abnormally low for its
spectral class.

   It is well known that there are no W UMa stars of
spectral class B. We come to the conclusion that CT Tau,
together with such stars as BH Cen, P = 0d.79, Sp B5, and
BZ Pyx, P = 0d.66, Sp B7V, constitutes a special group of
eclipsing variables. The data about these stars are taken
from "A Finding List for Observers of Eclipsing Variables"
by R. H. Koch et al. 1963.


                              I. M. ISTCHENKO
                    Tashkent Astronomical Observatory

                              P. F. CHUGAINOV
                    Crimean Astrophysical Observatory