COMMISSION 27 OF THE I. A. U.
        INFORMATION BULLETIN ON VARIABLE STARS
                    Number 2030 

                                 Konkoly Observatory
                                 Budapest
                                 1981 October 22

                                 HU ISSN 0374-0676





               STANDSTILL OF gamma CrB




  In the course of the photoelectric monitoring of low-amplitude 
delta Scuti stars we observed gamma CrB on four nights at Konkoly
Observatory. Throughout the observations the equipment was the
same as described by Kovacs (1981) for the 100cm telescope and
by Szabados (1977) for the 50cm telescope. Measurements were
taken only in V, using delta CrB as a comparison star in the cycle 
delta CrB, gamma CrB, sky with each observation consisting of three
(for the sky only one) consecutive 20s (at the 50cm telescope
10s) integrations.
  Differential magnitudes (in the instrumental system and not
corrected for differential extinction) are shown in Fig. 1.

                          [FIGURE 1]

 Fig. 1. Light curves of gamma CrB. The numbers on the right of each
 graph are the heliocentric Julian Dates of the first observation
 of each night minus 2440000. The instrumental differential
 v magnitude scale is the same for each graph as indicated and
 refer to the comparison star delta CrB in the sense m(var)-m(comp).
 The data on JD. 2444692 were obtained by the 100cm telescope,
 the others by the 50cm telescope.

Except for the linear trends and some suspected variations at
JD. 2444706, the light curves are constants within the error of
the measurements (i.e. 0.005-0.002 mag). The reason for the 
appearance of the linear trends in the data obtained by the 50cm
telescope is not known, but it may partly be accounted for the
colour dependent extinction not having been taken into consideration. 
The systematic difference between the average light
level of the data of the two telescopes may be due to the slight
difference between the two optical systems. This argument is
supported by the observations made simultaneously by the two
telescopes on 6/7th May, 1981 (UT), showing an average difference 
of ~~0.04 mag between the two light curves (because of the
very poor photoelectric quality of this night we have not published 
these data).
  Our data seem to support the results of Tippets and Wilcken
(1970) who found no observable variation of this star in contradiction 
to the observations of Percy (1970), showing light
variation of 0.02-0.05 mag on a time scale of ~~0.03 days. Probably 
this contradiction and the very early spectral type of
this star (A0 IV, according to the Catalogue of Bright Stars
(Hoffleit, 1964)) led Breger not to include gamma CrB in the latest 
list of delta Scuti stars (Breger, 1979).
  Though the light curves do not indicate any permanent variation, 
it is still useful to calculate the frequency spectrum
of the data. By use of the technique of Fourier analysis of 
unequally spaced data (Deeming, 1975), the power spectrum for all
our data was calculated and plotted (Fig. 2). Before calculating
the frequency spectrum, low frequency filtering (i.e. straight
line fitting) was applied for each night of observation. Though
close to the noise level, there are three well separated peaks
in the spectrum. Their frequencies and amplitudes (i.e. half of
their total variations) are: 5.06 c/d (0.0017 mag), 14.62 c/d
(0.0018 mag), 23.59 c/d (0.0014 mag). Leaving out the data 
obtained on JD. 2444706, the spectrum changed somewhat but not
radically (i.e. the features mentioned above were still observable 
within ~~1 c/d of the frequencies determined previously).
  For comparison, two of the light curves (labelled "B Filter
E.S.T. 1-7-69" and "B Filter 22-7-69" respectively) of Percy


                          [FIGURE 2]

 Fig. 2. Power spectrum of gamma CrB calculated by
 all the light curves plotted in Fig. 1.

                          [FIGURE 3]

 Fig. 3. Power spectrum of gamma CrB calculated by
 using the data of Percy (1970) (for details,
 see text).


(1970) were sampled at their observed points and analysed. The
power spectrum of these data is shown in Fig. 3. Because low
frequency filtering was not applied to these data, a considerable 
amount of power can be observed at the low frequency region. 
In spite of the complexity and unresolved nature of the
spectrum in Fig. 3, some similar features between the two power
spectra are suspected.
  At present we know nothing about the nature of gamma CrB. The
results of frequency analysis may indicate some sign of regularity. 
Nevertheless, the very small amplitudes of the light
variation in our observations can hardly be explained by a very
strong beat phenomenon. Whatever the reason for the light 
variation of gamma CrB, its nature seems to be quite different from
that of the normal delta Scuti stars.

  We are grateful to Dr. B. Szeidl for his valuable remarks
relating to the frequency analysis.





                       B. VETO and G. KOVACS
                        Konkoly Observatory
                            Budapest





References:
Breger, M.: 1979, Publ. Astron. Soc. Pacific 91, 5. [BIBCODE 1979PASP...91....5B ]
Deeming, T.J.: 1975, Astrophys. Space Sci., 36, 137. [BIBCODE 1975Ap&SS..36..137D ]
Hoffleit, D.: 1964, Catalogue of Bright Stars (New Haven, Conn.:
         Yale University Observatory). [BIBCODE 1964cbs..book.....H ]
Kovacs, G.: 1981, Acta Astr., 31, 75. [BIBCODE 1981AcA....31...75K ]
Percy, J.: 1970, Publ. Astron. Soc. Pacific 82, 126. [BIBCODE 1970PASP...82..126P ]
Szabados, L.: 1977, Mitt. Sternw. ung. Akad. Wiss., Budapest, No. 70. [BIBCODE 1977CoKon..70....1S ]
					[CoKon No. 70]
Tippets, R. and Wilcken, S.K.: 1970, Publ. Astron. Soc. Pacific
         82, 1156. [BIBCODE 1970PASP...82.1156T ]