COMMISSION 27 OF THE I.A.U.
         INFORMATION BULLETIN ON VARIABLE STARS
                      NUMBER 146

                                          Konkoly Observatory
                                          Budapest
                                          22 July 1966

  THE SECONDARY PERIOD OF THE RRab STAR Z CANUM VENATICORUM

	Photoelectric observations of Z CVn carried out in 1964 at
the Konkoly Observatory utilizing an EMI 9502B multiplier attached
to the 24" Newton telescope showed that the light curve changed 
periodically. During the spring of 1966 twelve maxima have been 
obtained, which enabled us to derive the secondary period:

			P_b = 22.75d

being the shortest one among the secondary periods so far known for
RRab stars.

			[FIGURE 1]

	The first column of the Table contains the observed maxima,
the second column the O-C values computed with the following elements:

	Max.hel. = 2439 172,602 + 0.6537975d E	(1)

In the third column the heights of the maxima relative to the comparison 
star are listed in blue (DeltaM_b) and yellow (DeltaM_y) in the
instrumental system.
	In the figure the DeltaM_b and O-C values obtained in 1966 are
plotted against the phase of the secondary period. The phase of the
secondary period was computed by the formula:

	Min.ampl. = 2439 176,12 + 22,75d		(2)



 J.D.max.	 O-C	 Mb	 My

2439172,593	-0,009d	+0,365	+0,655
    182,420	+0,011	 0,170	 0,450
    195,455:	 --	 0,380	 0,610
    216,395	-0,011	 --	 --
    240,581	-0,016 	 0,335	 --
    242,536	-0,022	 0,460	 0,670
    246,475	-0,006	 0,450	 0,750
    248,441	-0,001	 0,350	 0,640
    252,379	+0,014	 0,040	 0,375
    261,520	+0,002	 0,350	 0,695
    280,497	+0,018	 0,100	 0,400
    299,460	+0,021	 0,060	 0,390


							S. KANYO
							Budapest
                                                   Konkoly Observatory