COMMISSION 27 OF THE I. A. U.
        INFORMATION BULLETIN ON VARIABLE STARS
                    Number 1987

                                   Konkoly Observatory
                                   Budapest
                                   1981 July 7

                                   HU ISSN 0374-0676


     THE DISCOVERY OF 6.8 MINUTE OSCILLATIONS IN alpha Cir


   Rapid oscillations have been discovered in the cool magnetic
Ap stars HD 101065 (Kurtz and Wegner 1979), HD 24712 (Kurtz 1981),
HR 3831, and 33 Lib (Kurtz - unpublished). HR 3831 oscillates
primarily with a period of 11.67 minutes and 33 Lib (HD 137949)
oscillates with a period of 8.27 minutes. While searching for
more of these rapidly oscillating Ap stars, we have discovered
light variations with a period of 6.8 minutes in the F0p star
alpha Cir (HR 5463, HD 128898).
   Figure 1 shows a 6.5 hour long light curve of this star 
obtained by M.S.C. on 1981 May 02/03 with the University of Cape
Town photometer attached to the 0.75-m telescope of the South
African Astronomical Observatory (S.A.A.O.). The light curve is
divided up in to 1 hour sections which can be read continuously
from left to right, top to bottom. Each panel is 0.04 mag high
with the central solid line representing the mean magnitude of
the star for the night. The conditions on the night this light
curve was obtained were not good with some very light cirrus. Sky
transparency changes account for the slow erratic changes in this
light curve. Superimposed on the sky transparency changes are the
6.8 minute variations which are easy to see. Figure 2 shows an
amplitude spectrum of the light curve shown in Figure 1 where the
8.8 hour^-1 frequency stands out. The low frequency peaks in Figure

                         [FIGURE 1]

2 are due to the sky transparency changes. We have confirmed
these oscillations on several additional nights with one hour
observing runs using the S.A.A.O. 0.5-m telescope.
    This brings to five the number of rapidly oscillating Ap
stars known. The first author will publish a complete analysis
of these stars in the near future.


                        [FIGURE 2]




                          D.W. KURTZ,
                          M. S. CROPPER
                          Department of Astronomy,
                          University of Cape Town


References:


Kurtz, D.W., 1981, I.B.V.S., 1915.
Kurtz, D.W., and Wegner, G., 1979, Ap. J., 232, 510. [BIBCODE 1979ApJ...232..510K ]