COMMISSIONS 27 AND 42 OF THE IAU INFORMATION BULLETIN ON VARIABLE STARS Number 4026 Konkoly Observatory Budapest 16 May 1994 HU ISSN 0374 - 0676 FG Sge: RISE FROM MINIMUM FG Sge is a post-AGB star which displays strong changes of brightness. It brightened from 13.6 mag_pg. in 1894 to 9.6 mag(B) in 1965 (Herbig and Boyarchuk 1968) but only small variations were detected in recent years. Rapid decline of brightness began in August 1992 (Papousek 1992). The lightcurve of the decrease of brightness was published by Jurcsik (1992). FG Sge was observed with a CCD camera ST-6 attached to a Maksutov telescope 180/1000 mm in Ondrejov Observatory in 1992-1994. The observations were carried out in an instrumental V-band. FG Sge and the comparison stars were captured in the same image and the expositions lasted 60-120 seconds. The set of 2 or 3 comparison stars (always the same) was used for determining the brightness of FG Sge on each image and an average value was calculated. These data covering the mimimum and the rise of brightness are presented in this paper. FG Sge has a companion in a distance of 8 arc sec. Only the composed brightness of these two stars could be measured on the CCD images. The exact brightness of this companion has not been published so far but its approximate value is 12.5 mag(V). The brightness of this companion was determined using the spectrophotometric data of Stone et al. (1993). One of their observations was carried out on the same night as the data in this paper (JD = 48 956). Their magnitude of FG Sge alone was 13.06 mag(V) on this night. Brightness of the companion = 12.81 mag(V) was determined using the average of mag_tot.(V) in the CCD data No. 5, 6 and 7. The CCD data are listed in Table 1. The column mag_FG(V) refers to V-magnitude of FG Sge assuming brightness of the companion is 12.81 mag(V). The column mag_tot.(V) refers to the total brightness of FG Sge and its companion. The data in this column enable recalculating the magnitude of FG Sge when better data of the companion are known. The standard deviation of mag_tot.(V) lies in the range of 0.01-0.03 mag. Table 1: CCD data in 1992-1993. Mag_tot.(V) refers to the total brightness, mag_FG(V) refers to V-magnitude of FG Sge assuming brightness of the companion is 12.81 mag(V). N HJD mag_tot.(V) mag_FG(V) 1 48954.2863 12.14 12.98 2 48954.2877 12.14 12.98 3 48954.2905 12.10 12.91 4 48956.2508 12.07 12.83 5 48956.2563 12.15 13.01 6 48956.2702 12.19 13.09 7 48956.2716 12.18 13.08 8 48972.2241 12.05 12.79 9 48972.2262 12.04 12.78 10 49168.4282 11.56 11.97 11 49168.5029 11.46 11.84 12 49207.3622 11.05 11.29 13 49207.4231 11.07 11.31 14 49213.4201 11.02 11.25 15 49213.4237 11.00 11.23 16 49215.4637 10.98 11.21 17 49215.4463 10.95 11.17 18 49216.3632 10.95 11.17 19 49216.3700 10.99 11.21 20 49247.3435 11.00 11.23 21 49247.3473 10.99 11.22 22 49249.3104 11.02 11.26 23 49250.3263 10.98 11.20 24 49258.3338 10.93 11.15 25 49266.3327 10.92 11.13 26 49290.2979 10.74 10.92 27 49291.2690 10.67 10.83 28 49292.2350 10.65 10.81 [FIGURE 1] Figure 1: The lightcurve of FG Sge in November 1992 - October 1993 The CCD data are plotted in Fig. 1 together with the data of Stone et al. (1993) and of Jurcsik (1992). The variations of brightness of the order of several tenths of magnitude can be seen even in the time of the deep minimum. The timescale of these changes was several days long. The rise from minimum which had begun in 1993 continued in an irregular manner with a possible plateau on JD = 49 212- 49 250. I wish to thank dr. Hudec and Mgr. Pravec for making the CCD camera accessible to me. Vojtech SIMON Astronomical Institute 251 65 Ondrejov Czech Republic References: Herbig, G.H., Boyarchuk, A.A., 1968, Ap. J., 153, 397 [BIBCODE 1968ApJ...153..397H ] Jurcsik, J., 1992, IBVS, No. 3775 Papousek, J., 1992, IAU Circ., No. 5604 [BIBCODE 1992IAUC.5604....2P ] Stone, R.P.S., Kraft, R.P., Prosser, C.F., 1993, PASP, 105, 755 [BIBCODE 1993PASP..105..755S ]