COMMISSION 27 OF THE I.A.U. INFORMATION BULLETIN ON VARIABLE STARS Number 2967 Konkoly Observatory Budapest 19 December 1986 HU ISSN 0374 - 0676 OPTICAL BEHAVIOUR OF THE POLAR AM Her IN 1985 In linking to the sequence of comparison stars given by Hudec and Meinunger (1977) the star was measured and inspected on 131 blue-sensitive (ORWO-ZU 21 + GG13 + BG 12), 10 uv-sensitive (ORWO-ZU 21 + UG 2) and 12 photo- visual (ORWO-RP 1 + GG14) plates from 55 nights taken with the 50/70/172 cm Schmidt camera of Sonneberg Observatory covering the time interval between 11 February and 27 October 1986. The individual observations will be published in MVS, Sonneberg. On 44 nights more than one plate per night was obtained. Table I JD.hel. 244.. U-B B-V B 6645.392 -0.37:: 13m91:: 6645.427 -1.57 15.11 6645.440 0.51 15.11 6646.396 0.73 14.17 6646.439 -0.83 14.42 6648.396 -0.01 14.50 6648.410 -1.10 14.50 6648.439 -0.86 14.26 6649.388 0.93 14.48 6649.410 -0.86 14.48 6649.432 -1.00 14.34 6650.392 0.35 14.14 6650.411 -1.22 14.14 6650.430 -1.70 14.62 6651.399 -0.05 14.02 6651.420 -0.76 14.02 6651.443 -0.66 13.92 6679.330 -1.36 14.96 6679.351 -0.98 14.58 6679.371 0.59 14.58 6679.393 0.14 14.13 6683.337 -0.92 14.30 6683.358 -0.65 14.03 6683.379 0.05 14.03 6705.303 -0.96 13.76 6705.347 0.76 14.02 6709.298 -1.16 13.71 6709.308 0.69 13.71 6713.308 0.09 13.89 [FIGURE 1] [FIGURE 2] The long-time light curve in B and V (open circles) is given in Figure 1, As in the series of other years (see Gotz, 1986) two different states of brightness behaviour of AM Her can be seen there. The low state is characterized by a long-lasting minimum of 104d at the beginning of the series. Considering the light curve obtained in 1985 (Gotz, 1986) the given minimum is probably the continuation of the 120d low state at the end of the mentioned series. Assuming this case the total duration of the low state crossing the season 1985/86 amounts to about 290d. The light curve in Figure 1 shows also a minimum of about 20d and a short decrease to B=15m.0 within 10d. The observations of the high state which is caused by X-ray heating are in the mean brightness B=14m.0. The colour indices B-V and U-B of the star obtained on 11 nights are listed in Table I. 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. There, with increasing brightness the colour indices become larger. The occultation light changes from the high and low state observations superimposed on the long-time behaviour of the star are in agreement with the improved elements and the occultation light curves given by Gotz (1984). W. GOTZ Zentralinstitut fur Astrophysik der Akademie der Wissenschaften der DDR Sternwarte Sonneberg References: Gotz, W., 1984, IBVS, No. 2649. Gotz, W., 1986, IBVS, No. 2851. Hudec, R., Meinunger, L., 1977, MVS 7, 194.