COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                      NUMBER 346

                                   Konkoly Observatory
                                   Budapest
                                   1969 April 29

          A NOTE ON THE MAGNETIC VARIABILITY
               OF THE MAGNETIC STARS

      If we accept the model of the inclined rotator for
the magnetic stars, it ensues that the amplitude of the
change of the magnetic field is given by the expression
DeltaH_e ~ H_0e sin alpha_0 sin i, where alpha_0 is the angle between 
the axis of rotation and the magnetic axis of the star, i is
the angle between the line of sight and the axis of rotation
and H_0e is the effective field. It is evident that H_0e, alpha_0
and the equatorial linear velocity v do not depend on i.
In such a case the diagram (DeltaH_e, v sini) must represent a
dispersion of the points which correspond to the stars with
respective parameters about a straight line passing through
the beginning. Fig. I shows this diagram, where we have
made use of 21 stars, for which the necessary data are
available in [1,2]. On this diagram one can see two well
represented linear concentrations of the points with an 
interval of Delta_He between them of about 500-1000 gauss. There
is a tendency for the decrease of DeltaH_e with v sini, but the
fact, that at v sini = 0 km/s one observes stars with very
large Delta_He and that both linear concentrations of the points
do not tend toward the beginning of the diagram, is in
favour of the conclusion, that the hypothesis of the 
inclined rotator is not able to cope with the observational
data.


     Besides,  Fig. 2 shows the diagrams (DeltaH_e, B-V) and
(DeltaH_e, U-B), where we have made use of the data from [1,3].
Both diagrams present three well outlined zones in which
the points are concentrated. While on the diagram (DeltaH_e, B-V)
these zones are almost concentric with an approximate centre
B-V ~ 0,01 and DeltaH_e ~ 500 gauss, on the diagram (DeltaH_e, U-B)
these zones stretch in the direction of the negative values
of U-B. It is logical to group in zones the stars on these
diagrams. From the 40 stars we have made use of, they are
distributed on the diagram (DeltaH_e , B-V) as follows: in the
I. zone 21 stars, in the II. zone 14 stars, in the III. zone
2 stars, in the intermediate position between the I. and the
II. zones there are only 3 stars. They are set low and maybe
they represent the way of the passage of the stars from one
zone of the diagram into another. It is worth noting that
all stars attached to one of the groups alpha, beta, and gamma,
according to Babcock [4], lie in the same zone on both
diagrams and only 5 stars lie in different zones, i.e. the
zones are comparatively steady. Those two diagrams allow us
to associate the amplitude of the change of the magnetic
field DeltaH_e with the colour indices B-V and U-B and, hence,
with the temperature which supports the above mentioned
conclusion, that the change of the magnetic field is rather
a function of the astrophysical parameters of the stars and
not of the geometrical ones.


REFERENCES:
1. Babcock: ApJ Suppl. 3, 141 (1958) [BIBCODE 1958ApJS....3..141B ]
2. Boyarchuk and Kopylov: Isv. Krimskoi Astroph. Obs. 31, 44,
   (1964) [BIBCODE 1964IzKry..31...44B ]
3. Osawa: Annals of the Tokyo Astr. Obs., II serie, vol. IX. 123
   (1965) [BIBCODE 1965AnTok...9..121O ]
4. Babcock: in "Stellar atmospheres" ed. Greenstein, Univ.
   of Chicago Press 288 (1960)


Sofia, April 17, 1969. 


                         RACHO RADKOV
                    Astronomical Observatory
                     University of Sofia
                                     


			[FIGURE 1]
			[FIGURE 2]