COMMISSION 27 OF THE I. A. U.
          INFORMATION BULLETIN ON VARIABLE STARS
                      Number 905

                                     Konkoly Observatory
                                     Budapest
                                     1974 July 2


                NEW PERIODS OF THREE RR LYR VARIABLES

     The variables 10 in NGC 6333, 23 in NGC 5466 and 12 in NGC 6426
are three c-type RR Lyrae variables with the shortest periods (<0d.25)
in Oosterhoff type II globular clusters. Figure 1a shows the cumulative 
distribution for Oosterhoff II c-type variables (without omega Cen.).
The distribution clearly shows a gap at P=0d.024 at the shortest 
periods between these three variables and all the others. As the wings
of the cumulative distributions may be of great importance in the 
interpretation of the Oosterhoff effect, these three variables have been
carefully studied.

     NGC 6333 (M9) Var. 10 - This star has been studied only by H. B. Sawyer
(Toronto Publ. 1, No.24, 1951) who classified it as a c-type RR Lyr with
the period P=0d.242322. Using the same data the alternative period P=
=0d.319822 has been found, whose reciprocal differs by a unity from
the previous one. The light curve (Fig. 2) has the same dispersion as the
curve constructed with Sawyer's period.

     NGC 6426 Var. 12 - This variable has been discovered and studied
by C. Grubissich (Asiago Contr. 94, 1958) who found P=0d.23679 and the
extremely short alternative period P=0d.19145. Using the same data a
new possible period has been found, P=0d.310255, which differs from the
previous one by a unity in its reciprocal. The light curve Fig. 2 
constructed with this period however shows a larger dispersion, and new
observations are needed to decide about the right period.

     NGC 5466 Var. 23 - This star (Hop 235) has been discovered and
studied by T. I. Gryzunova (AC 526, 8, 1969; VS. Suppl. 1, 253, 1972. She
found P=0d.2321607, but P=0d.302353 gives a perfectly equivalent light
curve (Fig. 2).

This study, which cannot be considered conclusive in absence of near 
observations, reconfirms however the suspicion that the published periods
of these three variables might be wrong. On the basis of this hypothesis
and using the new periods found, the cumulative distribution for Oosterhoff 
II c-type variables has been plotted (Fig. 1b): the behaviour is now
more regular and continuous.


                          [FIGURE 1]
                          [FIGURE 2]


June 20, 1974.                                     CARLA CACCIARI
                                           Osservatorio Astronomico Univ.
                                           Via Zamboni 33,  40126 Bologna
                                                        Italy