COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                     Number 2384

                                      Konkoly Observatory
                                      Budapest
                                      15 August 1983

                                      HU ISSN 0374-0676



             ON THE PULSATION OF HD 201601



  The discovery of the pulsation of HD 201601 (HR 8097, gamma Equ) with a period
of 12.5 minutes by Don Kurtz (1982, priv. comm.) was an important contribution 
to the group of oblique pulsators (Kurtz, 1982). HD 201601 is particularly 
interesting since magnetic field variations with a period of about
72 years (Bonsack and Pilachowski, 1974) would imply an extremely slow 
rotation, if explained on the grounds of the oblique pulsator model.
  A unique feature of the short time scale pulsation of HD 201601 seems to
be that the amplitude is variable in time scales considerably shorter than the
magnetic field variations. A possible explanation could be that the magnetic
field variations are indeed of solar-cycle type, as suggested by Krause and
Scholz (1981) and that the rotation period is about 38 days (Kurtz, priv.
comm.).
  HD 201601 was observed in July 9, 10, and 11 1983 (UT) at the Mauna Kea
Observatory, Hawaii, using the 24" telescope of the University of Hawaii.

                      [FIGURE 1]

   Figure 1: Power spectrum of HD 201601 for July 10, 1983

                      [FIGURE 2]

   Figure 2: Power spectrum of HD 201601 for July 11, 1983

A classical single channel photon-counting photometer with a Johnson B-filter
and a 1.2D neutral density filter was used in combination with a RCA C31034A
photomultiplier. The observations are part of a survey for pulsating Ap stars
initiated at the European Southern Observatory, Chile, and at the Mauna Kea
Observatory. More details concerning the observation technique and reduction
can be found in Weiss (1984). In Figures 1 and 2 the best and worst case for
the power spectra are presented. In all three cases, however, the power peaks
at a frequency of about 0.079 (1/min) are clearly distinguishable from noise.
The amplitudes seem to be constant for all three nights and are estimated to
be about 0.8 mmag (B). A. final analysis of the data will be published 
elsewhere.



                 WERNER W. WEISS
                Institut fur Astronomie
                Turkenschanzstrasse 17
                A - 1180 Wien, Austria





References:
Bonsack, W.K., Pilachowski, C.A.: 1974, Astrophys. J. 190, 327 [BIBCODE 1974ApJ...190..327B ]
Krause, F., Scholz, G.: 1981, Upper Main Sequence. Chemically Peculiar Stars,
  Liege Coll. 23, 323  [BIBCODE 1981LIACo..23..323K ]
Kurtz, D.W.: 1982, Mon. Not. Roy. Astr. Soc. 200, 807 [BIBCODE 1982MNRAS.200..807K ]
Weiss, W.W.: 1984, Astron. Astrophys. (in prep.)