COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 3598 Konkoly Observatory Budapest 6 May 1991 HU ISSN 0374 - 0676 PHOTOGRAPHIC OBSERVATIONS OF V651 Mon DURING 1988-89 The central star of planetary nebula PK215+3d1 (V651 Mon) has been found to have unstable eclipses since 1981 (Kohoutek, 1982). Since then many authors have made a lot of photometric observations. They have revealed that this object has fast and complex variations in the light curves. We reported previously the photographic observations of the central star of planetary nebula PK215+3d1 for 1981-1986 (Hao, 1987) and 1987 (Hao, 1988). From these observations we have found that its drastic eclipsing light variations, started in 1981, decreased rapidly in 1986 and the eclipse became almost unseen in the light curves of 1987. Since then we continued the photographic observations during 1988-1989, using the 60/90/180cm Schmidt camera at Xiongliong station of the Beijing Observatory. The observing method and reduction techniques were used as previously described (Hao, 1987). The new photographic and photovisual observations for V651 Mon during 1988-1989 are presented in Table I. In this table the phases are calculated using the same ephemeris as before (Hao, 1987). In order to make a comparison with the observations in 1987 we also present the light curve of 1987 in Figure 1. The light curves of 1987, 1988, 1989 are plotted on the same magnitude scale. From these observations we can state that the brightness variations of the central star of planetary nebula PK215+3d1 have an obvious difference between 1987 and 1988. We found that the eclipse events nearly unseen in the light curve of 1987 reappear in the light curves of 1988. The amplitude of the light fluctuations is about 1.1 mag and the "eclipse" occupied roughly 40% of the orbital period. The maximum brightness (mpg) in 1988 was brighter than in 1987. From these it is reasonable to think that the binary central star of planetary nebula V651 Mon might undergo another mass ejection from the sdO component during 1987-1988. From the observations of 1989 it can be stated that the eclipse event existed in 1989 and its amplitude was about the same as in 1988. [FIGURE 1] Figure 1. The light curves of V651 Mon Table I. The Observations of V651 Mon No. Plates No. J.D.hel. M_pg Phase QA- 2447000+ 1 1027 259.325 11.38 0.319 2 1030 260.320 11.12 0.382 3 1031 261.301 11.00 0.443 4 1034 264.331 11.06 0.633 5 1035 265.312 10.67 0.694 6 1038 266.323 11.00 0.758 7 1039 267.364 11.10 0.820 8 1040 270.309 10.96 0.007 9 1043 271.325 11.14 0.071 10 1044 272.317 11.74 0.133 11 1045 274.309 11.80 0.258 12 1048 275.318 11.05 0.322 13 1049 276.306 10.17: 0.383 14 1052 278.319 11.04: 0.509 15 SD-2906 642.344 10.67 0.322 16 -2907 643.345 10.12 0.385 17 -2908 644.349 11.19 0.448 18 -2909 652.349 10.80 0.949 19 -2911 657.345 10.00: 0.262 M_pv 20 QA-1028 259.334 11.00 0.320 21 1029 260.302 11.03 0.380 22 1032 261.313 11.20 0.444 23 1033 264.506 11.24 0.644 24 1036 265.326 11.05 0.695 25 1037 266.309 11.29 0.757 26 1041 270.325 11.40 0.008 27 1042 271.310 11.50 0.070 28 1046 274.323 11.51 0.259 29 1047 275.307 11.60: 0.321 30 1050 276.319 11.11 0.384 31 1051 278.309 11.52: 0.509 32 SD-2910 657.358 10.96 0.263 HAO XIANG-LIANG Beijing Observatory Academia Sinica Beijing, China References: Hao, X.-L.: 1987, IBVS No. 3014. Hao, X.-L.: 1988, IBVS No. 3271. Kohoutek, L.: 1982, IBVS No. 2113. ERRATUM In the No. 3515 issue of the IBVS, in Figure 2 the lowest panel shows the magnitudes of HK Aqr (Gl 890). The star name HR Aqr is erroneously drawn in the Figure. N.I. BONDAR'