COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                      NUMBER 566

                                  Konkoly Observatory
                                  Budapest
                                  1971 July 6


        ON THE DISTRIBUTION OF FLARE STARS IN THE
                 PLEIADES CLUSTER

       In the paper entitled "Unusual Distribution of
flare stars in Pleiades" L.V. Mirzoyan and M.A. Mnatsakanian
(1) affirmed that there are no flare stars in the central
volume of the Pleiades cluster within the radius 1.4 pc.
They suggested that the existence of such a "cavity" might
be explained "in the frames of the idea of expansion of
stellar associations". However, there is no need to such an
idea as the phenomenon treated by the above mentioned
authors is only an apparent one.
      In Fig. 1 the curve of radial distribution of the
surface density (per square degree) for flare stars brighter
than 18.5m in the Pleiades region is given. It is taken from
our paper (2) with somewhat more details. The sample of
flare stars considered here was taken from papers (3) and
(4). The vertical lines correspond to the possible errors
of surface densities F(r) determined by the formula F(r)/n^1/2,
where n is the number of stars used for the calculation of
the given value of F(r). Within the range of these errors
we must use the curve of distribution F(r) which shows the
increase of flare stars density to the very centre of the
cluster (curve above). The curve below represents the 
corresponding spatial density distribution f(r).
      The fainter flare variables are also concentrated
to the centre of the cluster, and further discoveries of
new flare stars in the Pleiades region (5) do not change
this conclusion.
      The density distribution of flare stars in the
Pleiades cluster is the same as that of brighter members
of the cluster. The only difference (the less concentration)
is due to smaller masses of the flare stars.
      Fig. 1 contradicts the picture given in paper (1),
Results announced in paper (1) are evidently explained by
using too narrow zones for star counts and by neglecting
the natural uncertainty of the F(r) values derived.


                       [FIGURE 1]


Sternberg Astronomical          P.N. KHOLOPOV
Institute, Moscow


(1) L.V. Mirzoyan, M.A. Mnatsakanian, IBVS N528, 1971. [BIBCODE 1971IBVS..528....1M ]
(2) P.N. Kholopov, Astron.Journ, 48, 529, 1971.  [BIBCODE 1971AZh....48..529K ]
(3) G. Haro, E. Chavira, Tonantzintla y Tacubaya, Bol., 5,
   23, 1969. [BIBCODE 1969BOTT....5...23H ]
(4) V.A. Ambartsumian, L.V. Mirzoyan, E.S. Parsamian,
   O.S. Chavushian, L.K. Erastova, Astrophysics, 6, 7, 1970. [BIBCODE 1970Ap......6....1A ]
(5) V.A. Ambartsumian, L.V. Mirzoyan, E.S. Parsamian,
   O.S. Chavushian, L.K. Erastova, Byurakan. Obs. Preprint,
   N2, 1971.