COMMISSION 27 OF THE I.A.U. INFORMATION BULLETIN ON VARIABLE STARS Number 3271 Konkoly Observatory Budapest 5 December 1988 HU ISSN 0374 - 0676 PHOTOGRAPHIC OBSERVATIONS OF V651 Mon, THE CENTRAL STAR OF THE PLANETARY NEBULA NGC 2346 The central star of planetary nebula NGC 2346 (AGK3-0965) is known to be a spectroscopic binary with a period of about 16 days (Mendez 1980). From at least 1899 to 1981 Nov. it did not vary in brightness (Schaefer 1983). But in 1981 Dec. unexpected large amplitude eclipse variations in brightness were observed (Kohoutek 1982). Since then a lot of observations have been reported by many authors as Kohoutek (1983), Feibelman and Aller (1983), Marino and Williams (1983, 1984), Schaefer (1985), Jasniewicz and Acker (1986) and others. They have revealed that the central star of NGC 2346 showed fast and complex light variations due to eclipse and the amplitudes of the eclipse varied rapidly. We have observed the the planetary nebula NGC 2346 since 1981 and found that its eclipse amplitude rapidly decreased in 1986 and pointed out that the amplitudes would be decreasing (Hao 1987). In this paper we present new photographic observations made in March and April 1987 using the 32/385 cm refractive telescope at the QingDao observatory. The plates and filter combination used for the photographic and photovisual magnitudes were Eastman Kodak-103aO (or IIaO) and Kodak- 103aD + GG14 respectively. The method of the magnitude determination is described by Hao (1987). From these we obtained the m_pg and m_pv, the results are given in Table I and Table II respectively. The photographic light curves we obtained in 1985, 1986 and 1987 are plotted in Figure 1. In Figure 2 the photovisual light curve is plotted. The magnitudes in Table I and II contain contributions from both the central star and the nebular radiations. From these observations we can state that the brightness variations of the central star of planetary nebula NGC 2346 have an obvious difference from 1985 to 1987. The eclipse amplitude is decreasing rapidly from 4.0 (1985), 1m.1 (1986) to about 0m.4 (1987). The fluctuation in the light curve is increasing in 1987 even we could not see the eclipse variations in photographic region. Table I No Plates No. J.D.hel. M_pg Phase QA- 2446000+ 1 1003 870.978 11.13 0.982 2 1004 871.983 11.49 0.045 3 1005 872.972 11.41 0.170 4 1008 879.990 11.26 0.540 5 1010 880.985 11.35 0.609 6 1011 887.971 11.34 0.047 7 1014 901.003 11.22 0.864 8 1015 901.985 11.30 0.925 9 1017 902.986 11.27 0.957 10 1018 906.983 11.20: 0.238 11 1021 907.996 11.33 0.302 12 1022 908.985 11.38 0.364 13 1025 911.984 11.39 0.552 14 1026 913.997 11.40: 0.678 Table II No Plates No. J.D.hel. M_pg Phase C QA- 2446000+ 1 1006 837.991 11.43 0.171 -0.02 2 1009 880.927 11.38 0.608 -0.03 3 1012 887.984 11.52 0.048 -0.18 4 1013 900.988 11.33 0.863 -0.11 5 1016 901.998 11.37 0.926 -0.07 6 1019 906.996 11.27 0.239 -0.07 7 1020 907.983 11.25: 0.301 0.08 8 1023 909.010 11.17 0.365 0.21 9 1024 912.015 11.30 0.554 0.08 [FIGURE 1] Figure 1. The light curves of AGK3 - 0965. Phases were computed using the elements given by Hao (1987). [FIGURE 2] Figure 2. The light curve of AGK3 - 0965 (photovisual magnitudes). The maximum brightness (m_pg) of this object showed no obvious change between 1985 and 1986 but in 1987 increased by about one magnitude (11m.2). The variation of minimum brightness is larger than that of the maximum brightness (m_pg nearly 14.0m in 1985 to about 11.5m in 1987). From Figure 2 it seems that the eclipse variation still exists and its amplitude is only about 0.35 mag. which is smaller than in 1986. HAO XIANG-LIANG Beijng Observatory Academia Sinica Beijing, China References: Feibelman, W.A. and Aller, L.H. 1983, ApJ., 270, 150. [BIBCODE 1983ApJ...270..150F ] Hao, X.L., 1987, IBVS, No. 3014. Jasniewicz, G., and Acker, A., 1986, As. Ap. 160, L1. [BIBCODE 1986A&A...160L...1J ] Kohoutek, L., 1982, IBVS, No. 2113. Kohoutek L., 1983, MN, 204, 93p. [BIBCODE 1983MNRAS.204P..93K ] Marino, B.F., and Williams, H.O., 1983, IBVS, No. 2266. Marino, B.F. and Williams, H.O., 1984, IBVS, No. 2583. Mendez, R.H., 1980, IAU Symposium No. 88, 567. [BIBCODE 1980IAUS...88..567M ] Schaefer, B.E., 1983, IBVS, No. 2281. Schaefer, B.E., 1985, IAU Circ., No. 4027. [BIBCODE 1985IAUC.4047....2S ]