COMMISSION 27 OF THE I. A. U.
          INFORMATION BULLETIN ON VARIABLE STARS
                      Number 2306


                                      Konkoly Observatory
                                      Budapest
                                      5 April 1983

                                      HU ISSN 0374 - 0676


          ON THE SHORT TIME SCALE PERIOD OF alpha Cir*


  Alpha Cir (HD 128898, Ap(SrCrEu), m_v =3.15) was observed at ESO, La Silla,
with the Walraven 5-channel photometer attached to the 90 cm Dutch telescope
during the night of July 23 to 24, 1982. Simultaneous measurements through
V, B, L, U and W filters were obtained during about 2h40m of continuous 
observations. An integration time of 16 sec was used throughout.
  The importance of such multichannel observations lies in the determination 
of phaseshifts between different colours which allow for the discrimination 
of different pulsation modes (Balona and Stobie, 1979 and subsequent
papers).
  Already the first crude reductions following the observations in the same
night proved the presence of short time scale variations of alpha Cir as it was
discovered by Kurtz and Cropper (1981). The object seems to have a variable
pulsation amplitude which would allow establishment of constraints on i and
 as well as an independent determination of the rotational period. These
assumptions are based on the validity of the oblique pulsator model for 
pulsating Ap stars as it is proposed by Kurtz (1982).
  Our observations in B, corrected for a mean extinction, are plotted in
Fig. 1 and the corresponding power spectrum is presented in Fig. 2. No 
aliasing problems are evident and a pulsation frequency of

                        [FIGURE 1]

* Based on observations obtained at ESO, La Silla

                        [FIGURE 2]

     f = 8.78 (hr^-1)          [(6.834 +- 0.01)min]

was determined. The amplitude of pulsation was about 0.01 mag in this night
and thus considerably larger than in May 2 to 3, 1981 (Kurtz and Cropper,
1981).
  A full analysis of the data is in progress and will be published later.
With HD 101065 (Weiss and Kreidl, 1980) this is the second pulsating Ap star
so far observed at ESO.



      HARTMUT SCHNEIDER              WERNER W. WEISS
      Universitatssternwarte         Institut fur Astronomie
      Gottingen, BRD                 Wien, Austria


References:

Balona, L., Stobie, R.S.: 1979, Mon. Not. Roy. Astron. Soc., 189, 649. [BIBCODE 1979MNRAS.189..649B ]
Kurtz, D.W.: 1982, Mon. Not. Roy. Astron. Soc., 200, 807. [BIBCODE 1982MNRAS.200..807K ]
Kurtz, D.W., Cropper, M.S.: 1981, Inf. Bull. Var. Stars, No. 1987.
Weiss, W.W., Kreidl, T.: 1980, Astron. Astrophys., 81, 59. [BIBCODE 1980A&A....81...59W ]