COMMISSION 27 OF THE I. A. U.
           INFORMATION BULLETIN ON VARIABLE STARS
                       Number 2772

                                       Konkoly Observatory
                                       Budapest
                                       8 August 1985

                                       HU ISSN 0374 - 0676


        VARIATIONS OF THE RADIATION FLUX FROM THE MAGNETIC
       VARIABLE STAR beta CrB IN THE DEPRESSION lambda 5200 Angstrom

 A famous chemically peculiar star beta CrB (F0p, V=3.47mag) was observed by using
the spectrophotometer in the range Deltalambda=30 angstrom, being centered at lambda c=5215 angstrom falling
into depression at lambda 5200 angstrom.
 The observations were carried out during ten nights, from 18 May till 6 June
1984. The star gamma CrB was adopted as a comparison star. The differential 
extinction of beta CrB versus gamma CrB was accounted upon. The value of the atmospheric
extinction was estimated with respect to the star eta UMa. The brightness 
magnitudes of beta CrB and gamma CrB were estimated alternatively, 1.0 minute long each.
As a result of the observations, we obtained the values Delta m=m gamma-m beta with the time
resolution 2 min.

 The periodic variations were searched for during all the 10 nights (total
number of measurements was N=551) within the interval 50-500 min. The basic
methods used were those of Yurkevich (1971) and Deeming (1975). It has been
found, that the variations of radiation flux do exist and could be described
by a superposition of three sinusoidal oscillations with the periods P1 =196.9mag,
P2 =158.3mag and P3=58.6mag.

 The values of amplitudes being estimated by the method of Yurkevich and
Deeming are in good agreement and correspond to A1 =0.005mag, A2 =0.004mag and A=0.004mag
for P1, P2 and P3, respectively. The power spectrum and the function of spectral
window obtained by the method of Deeming are presented in Figure 1. At the top
the mean curve of Delta m variations is shown for the above indicated periods 
calculated by the method of Yurkevich. Absence of any significant peak in the
function of spectral window for the periods around P1, P2 and P3 on one hand
and presence of the conjugate periods determined by the time gaps of sidereal
day confirm reliability of the obtained results.

 In Figure 1 the conjugate and basic periods are connected by a solid line.
The averaged values of Delta m for one night and the magnetic field variations with
the period of the stellar rotation are compared in Figure 2.

 Finally we have come to a conclusion that there exist two types of brightness


variations of beta CrB in the range of lambda 5200 angstrom. They are: a) well - pronounced
variations of Delta m with the phase of star rotation that can be properly 
explained in the frames of an oblique rotator model (see Figure 2) and b) complex
quasi-periodic variations of Delta m during one night, which might be caused by
pulsations of this star.


                              [FIGURE 1]
                              [FIGURE 2]




N. POLOSUKHINA, V. MALANUSHENKO, V. BURNASHEV
Crimean Astrophysical Observatory
Nauchny, Crimea, SU - 334413. USSR



References:
Deeming, T.J., 1979, Astrophys.Space Sci., 36, 137. [BIBCODE 1975Ap&SS..36..137D ]
Yurkevich, I., 1971, Astrophys. Space Sci., 13, 154. [BIBCODE 1971Ap&SS..13..154J ]