COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                      NUMBER 764

                                    Konkoly Observatory
                                    Budapest
                                    1973 February 6




  DEVELOPMENT OF A NEW 4-YEAR CYCLE IN THE 41-DAY PERIOD OF
                        RR LYRAE


Long series of our photoelectric observations of RR Lyrae made
a 4-year period in the variations connected with the 41-day 
cycle evident. (Detre, L., Szeidl, B., Proc. 41 IAU Colloquium, 
Toronto 1972, in press) In the fall of 1970 and early 1971 the amplitude 
of the 41-day cycle became again very small indicating the
near end of the last 4-year cycle.
In order to study the transition from the old cycle to the 
expected new one we observed the star photoelectrically in B, V
at our 24-inch reflector every night in the past two years whenever 
it was possible (20 maxima and 28 rising branches in 1971
while 29 maxima and 30 rising branches in 1972).The results for the
visual maxima and phase shifts of the median brightness are shown
in the Figure. The phases are calculated by using the formulae given 
in Detre, L., 1970, Ann.d.Univ.-Sternwarte Wien, Bd. 29.,Nr. 2., p. 89.
and shown in the Figure.
At the end of the 4-year cycle the phase variations during the 41-
day cycle died almost completely down and then the new cycle started 
with a rapid increase of the amplitude of the phase oscillation.
The amplitude of the maximum-variations was only 0.07m at the end
of the old cycle (June 1971) and then it became very rapidly as
large as 0.16m (October 1977). By the beginning of the 1972 observing
period the amplitude of the maximum-variations had approached its
maximum value and was nearly constant (0.25m in April and 0.28m in
October 1972)
The most interesting was the phase shift in the 41-day period. O'-C'
was about +19d during the whole old cycle till June 1971 while it.
has been +29d for the new one since July 1971. Consequently, the 
beginning of the new cycle was accompanied by an abrupt phase shift
of 10 days, about the fourth of the 41-day period. During one and
the same 4-year cycle the 41-day period remained constant.



                          L. DETRE and B. SZEIDL
                           Konkoly Observatory
                                Budapest


                     [FIGURE 1]