COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                     Number 2237

                                    Konkoly Observatory
                                    Budapest
                                    1982 November 30

                                    HU ISSN 0374-0676



        SHORT TIME SCALE LIGHT VARIATIONS OF 21 COMAE



  Differential photometric measurements of 21 Com were made in the B band
with the 60 cm Cassegrain telescope of the Astronomical Institute of
Wroclaw University in Bialkow. On six nights more than 950 individual 
measurements were obtained. The observations cover about 30 hours, which is
comparable to the whole observational time of the so far published photometric
measurements of 21 Com with time resolution of minutes. As comparison stars
17 Com B and 18 Com were used.
  The period of 32 minutes reported by Hahner and Mavridis (1957), Percy
(1973), (1975) and by Weiss et al. (1980) has not been confirmed. This is
in accord with a recent result of Jarzebowski (1982).
  We performed frequency analysis of our data in the range from 6 to 420 c/d.
Two highest peaks in the Fourier transform occurred at nu1=244.24 c/d-P1~=5.9 min
and nu2=267.11 c/d-P2~=5.4 min. After prewhitening the data with one of the
above mentioned frequencies the amplitude of the other did not change. Both
these frequencies are similar to those found recently by Kurtz (1982) in
five other cool Ap stars. The amplitudes of light variations corresponding
to the frequencies we found are practically the same and equal to
0.00147 +/- 0.00034 mag. Because of the low signal to noise ratio the reality
of these frequencies requires independent confirmation.


B. MUSIELOK                        T. KOZAR

Astronomical Institute             51-657 Wroclaw, ul. Kazimierska 17/32
of the Wroclaw University          Poland
51-622 Wroclaw, ul. Kopernika 11
Poland


References:

Bahner, K., Mavridis, L., 1957, Z. Astrophys. 41, 254 [BIBCODE 1957ZA.....41..254B ]
Jarzebowski, T., 1982, Symp. "Magnetic and Variable Stars" Szombathely [BIBCODE 1982CoKon..83..190J ]
								[CoKon No. 83]
Kurtz, D.W., 1982, Monthly Notices Roy. Astron. Soc. 200, 807 [BIBCODE 1982MNRAS.200..807K ]
Percy, J.R., 1973, Astron. Astrophys. 22, 381 [BIBCODE 1973A&A....22..381P ]
Percy, J.R., 1975, Astron. J. 80, 698 [BIBCODE 1975AJ.....80..698P ]
Weiss, W.W., Breger, M., Rakosch, K.D., 1980, Astron. Astrophys. 90, 18 [BIBCODE 1980A&A....90...18W ]