COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                      NUMBER 865

                                Konkoly Observatory
                                Budapest
                                1974 February 6



PERIODICAL COMPONENT IN THE LIGHT CURVE OF R CORONAE AUSTRINAE



   R CrA undoubtedly belongs to the class of Ins variable
stars. This is confirmed by its connection with a cometary nebula, 
rapid irregular variations of its brightness and its spectral 
peculiarities. But by the method of sliding differences
(1,2) a periodical component in the light variations of the
star was discovered. Fig. 1 shows the mean difference as a function 
of time interval. The long sequence of Jones' observations
(3) was used. The brightness is expressed in intensity scale.

                     [FIGURE 1]

                     [FIGURE 2]

Each point is obtained from 310 differences in average.
 The regularity cannot be explained by axial rotation of the star by analogy 
with RW Aur (2). The curve considerably differs from analogous curves for 
the solar activity and RW Aur. Instead of fading of the amplitude with 
increasing time interval one can see its rise. A drift of the second
minimum in the direction of the longer time intervals is also absent. 
Absence of the fading of the mean difference curve and an
accurate multiplicity of the time intervals between the first and
the second minima can be explained by some periodical light variations 
with a constant initial phase. We have found

             Max_2 = 2426497 + 65.67d E
               
and obtained the mean curve (Fig. 2).
The curve is obtained from all the published observations (n=3407,
JD 2426537 - 2440861). The very large dispersion of the mean curve
(Delta m = +- 0.6m) considerably exceeds the probable accidental error
of the observations.
   Fig. 2 shows a peculiarity of the light curve. It consists of
two light waves with maxima a half of the period away.The waves differ 
from each other in amplitude.The first is larger than the second.
The main maximum has a symmetrical shape.
   A relation between the light curve shape and the mean brightness 
is detected. The curves for four intervals of mean brightness 
are shown in Fig. 3. As the brightness weakens the difference 
between the two maximum heights decreases.
   The brightness of the star has two fluctuations. Regular
fluctuations interfere with rapid and irregular ones. The amplitude 
of the periodical fluctuations is some three times smaller
than the amplitude of the irregular fluctuations. Herein is the
reason why the periodicity in the brightness variations was unknown
though there are long sequences of observations.
  It is not probable that a star has both periodical pulsations 
and irregular light variations with larger amplitude simultaneously.
Duplicity of the star is more obvious.

                     [FIGURE 3]

  It is impossible to work out a model of a system only on the base
of visual estimates of a star brightness without accurate colorimetric 
and spectral data. The light variations of the system are 
evidently under the influence of a gas nebula into which it is immersed.



                            I. M. ISHCHENKO
                      Physics department of the Tashkent
                      Electrotechnical Institute of
                      Communications.



    References
1   I.M. Ishchenko, VS 16, No. 2, 157, 1967. [BIBCODE 1967PZ.....16..157I ]
2   I.M. Ishchenko, VS 18, No. 3, 293, 1972. [BIBCODE 1972PZ.....18..293I ]
3   Jones A., NZAS Circ. No. 23-133.