COMMISSION 27 OF THE I.A.U.
                 INFORMATION BULLETIN ON VARIABLE STARS
                             Number 3279

                                                         Konkoly Observatory
                                                         Budapest
                                                         2 January 1989

                                                         HU ISSN 0374 - 0676


          OPTICAL BEHAVIOUR OF THE POLAR AM Her IN 1988

Using the sequence for comparison stars given by Hudec and Meinunger (1977)
we measured the star on 55 blue-sensitive (ORWO-ZU21+GG13+BG12), 33 photovisual 
(ORWO-RP1+GG14) and 41 uv-sensitive (ORWO-ZU21+UG2) plates from 40
nights taken with the 50/70/172 cm Schmidt camera of Sonneberg Observatory
covering the time interval between 14 February and 7 November 1988. The
individual observations will be published in MVS, Sonneberg.
   The annual light curves in B, V and U are given in Figure 1, where all
observations show the star to be in the high state caused by X-ray heating.
The annual mean brightness amounts to B=13.38m, V=13.34m and U=12.34m.
The mean value in B is brighter than in the previous year (Gotz, 1987).
   From 29 nights we obtained 36 B-V colour indices, and 37 U-B colour
indices. The B-V colour indices complete the colour-magnitude diagram
m_B-(B-V) given by Gotz (1984) and are in agreement with the behaviour shown
there. The colour-magnitude diagram m_B-(U-B) is given in Figure 2. It is
similar to that given by Gotz (1986) but with higher mean B-brightness
without any colour index change. In both cases, the U-B colour indices become 
larger with increasing brightness.
   The two-colour diagram (U-B)-(B-V) of the series 1988 is shown in Figure 3.
There the B-V colour indices become larger with decreasing U-B. This
behaviour also confirms the result obtained from observations of the series
1986 given by Gotz.


                          [FIGURE 1]
                          [FIGURE 2]
                          [FIGURE 3]
                          [FIGURE 4]


   In order to study the influence of occultation light changes on the
overall light curves, all observations were reduced to one common epoch
by means of the improved orbital elements published by Gotz (1984). As it is
shown in Figure 4, where the mean magnitudes in B, V and U are plotted against
the phases, periodic variations can only be seen in the V range.



                    W. GOTZ

          Zentralinstitut fur Astrophysik
          der Akademie der Wissenschaften
           der DDR, Sternwarte Sonneberg



References:

Hudec, R., Meinunger, L., 1977, MVS 7, 194.
Gotz, W., 1984, IBVS, No. 2649.
Gotz, W., 1986, IBVS, No. 2967.
Gotz, W., 1987, IBVS, No. 3126.