COMMISSION 27 OF THE I. A. U.
           INFORMATION BULLETIN ON VARIABLE STARS
                      NUMBER 737

                                   Konkoly Observatory
                                   Budapest
                                   1972 November 14


            THE SECONDARY PERIOD OF RV CAPRICORNI


Although RV Cap is one of the brightest RRab stars showing
Blashco-effect, it was not yet photoelectrically observed.
From his visual observations Tsessevich (Trudi GAIS 23,1953)
gave a secondary period of 221,86 days for this star which
was the longest one known among the RRab variables.
During several stays at the Catania Astrophysical Observatory 
on Aetna in the years 1970-71-72 I carried out photoelectric 
observations of the star to determine a more accurate 
length of its secondary period.
The observations were taken with the Cassegrain reflector of
61 cm aperture and 600 cm focal length, equipped with a three
colour synchronous-photometer containing EMI 6256 photomultiplier 
tubes.
Together 15 ascending branches and maxima were obtained well
distributed over the phases of the secondary period, for which
I have got the value:

              P'= 138.3d

This period is much shorter than that given by Tsessevich, and
even if it remains the longest secondary period so far known
for RRab variables, it is now much better fitting the distribution 
of the lengths of secondary periods.
The Table contains the observed maxima in three colours DeltaMy,
DeltaMb and DeltaMu and their elements:
    
    Max.hel.= 2439032,819 + 0.44775015d E    (1)

In the Figure the values of DeltaMv and O-C are plotted against
the phase of the secondary period computed by the formula

  Lowest Max. - 2441177.71 + 138.3d N        (2)

While there is only insignificant scattering at highest 
amplitudes in the DeltaMv-values, at the same phase the O-C values
indicate a larger scattering resulting from the double hump
appearing at these maxima of the light curve, like in the case
of AR Her. The height of the humps are changing, one is increasing 
when the other is decreasing, and in a certain moment the
maximum of the light curve jumps from one hump to the other
one.
   I am very grateful to Prof. G. Godoli for having given
me opportunity for observing in the Catania Observatory and
I thank very much Prof. M. Rodono, S. Catalano and Dr. Blanco
for making the observations, when I could not take part in
them.

---------------------------------------------
J.D.max.     O-C   DeltaMy  DeltaMb  DeltaMu
---------------------------------------------
2440
  721,62: -0,092       -        -        -
  790,520   ,157     +0,37    -0,13    -0,21
  794,552   ,155     +0,30    -0,20    -0,30
  798,587   ,151     +0,26    -0,22    -0,38
41146,554   ,144     +0,50     0,0     -0,05
  147,446   ,148     +0,47:    0,0     -0,05:
  151,475   ,149     +0,50    +0,01    -0,06
  155,500   ,154     +0,55    +0,05    -0,01:
  163,551   ,164      -       +0,03    -0,10
  173,41:    -        -       +0,07     -
  177,431   ,166     +0,60:   +0,105   +0,04:
  180,568   ,164     +0,57:   +0,085   -0,03
  186,388   ,165     +0,56    +0,085   -0,02
41507,478   ,097     +0,14    -0,46    -0,70
  515,533   ,102     +0,13    -0,39    -0,61
---------------------------------------------


                    [FIGURE 1]




                              S. KANYO
                           Konkoly Observatory
                              Budapest