COMMISSIONS 27 AND 42 OF THE IAU INFORMATION BULLETIN ON VARIABLE STARS Number 3877 Konkoly Observatory Budapest 6 May 1993 HU ISSN 0374 - 0676 CCD TIMES OF MINIMA OF FAINT ECLIPSING BINARIES The list of times of minima of 24 eclipsing binaries is presented. The minima have been obtained with the SBIG ST-6 CCD camera and a 18-cm f/5.6 Maksutov reflector at the Ondrejov Observatory in January and February 1993. Although the camera is mainly used for solar system studies, a part of observational time was devoted to eclipsing binaries too. The aim of the present observations was to derive the times of minima of relatively faint stars (11.5-13.5 mag in maximum) with the precision of about 5 minutes. As stars with large amplitudes (0.8 mag or more) and relatively rapid light changes were chosen, nearly 10 measurements during the eclipse were sufficient to reach the desired precision. This enabled to observe more (up to four) stars simultaneously. The camera was used without any filter and only magnitudes in the instrumental, red sensitive (close to the R band) system could be obtained. The exposure times were 60-120 s. The relative precision of a single measurement was 0.03 mag for stars brighter than 14th mag and typically 0.09 mag for stars between 14-15th mag. Table 1: Times of minima of eclipsing binaries. Star minimum error n O-C O-C Ref. d HJD- (GCVS) (2) (h) 2 400 000 CI Aur 49028.400 0.003 13 +0.082 -0.013 (1) 0 EQ Aur 49004.438 0.003 14 -0.362 3.0 LV Aur 49018.502 0.008 13 -0.189 (2) MO Aur* 49004.449 0.002 10 0 QT Aur 49018.379 0.004 11 +0.020 (2) 0 TY Cnc 49006.507 0.002 8 -0.163 AE Cnc 49006.495 0.004 8 -0.007 RY CMi 49031.385 0.002 9 -0.822 0.3: AE Cas 49031.556 0.001 8 +0.068 0 AV Cep 49031.420 0.002 12 +1.087 +0.018 (3) 0 AN Gem* 49018.468 0.002 11 -1.613 1.7 CX Gem 49002.520 0.001 12 -0.007 0 EG Gem 49006.511 0.001 8 +0.205 -0.011 (1) HI Gem* 49004.397 0.005 12 +0.014 (4) 5.5 AG Lac 49018.261 0.002 8 -0.310 0: RY Lyn 49020.568 0.002 11 -0.024 0 VX Mon 49029.364 0.003 8 -0.601 BZ Mon 49005.384 0.003 10 -0.117 -0.019 (1) 1: NN Mon* 49002.541 0.002 13 +0.468 0 V456 Mon 49005.434 0.002 7 -0.051 QT Ori 49002.336 0.003 10 -0.497 0.7 FQ Per 49005.479 0.003 13 +0.556 3.0 LS Per 49005.338 0.002 12 -0.306 +0.013 (1) 0 TW UMa 49020.554 0.002 12 -0.075 1.1 References: (1) Borovicka (1993a); (2) Splittgerber (1985); (3) Manek (1992); (4) Borovicka (1993b) The results are given the Table 1. All minima are primary. The following data are given: The star name, the heliocentric time of minimum, the error of minimum, the number of images used, the O-C value relative to the linear light elements from the 4th edition of the General Catalogue of Variable Stars (GCVS), the O-C relative to more recent light elements (if any), the reference to the recent elements. In one case (MO Aur) only the present observation enabled the first determination of the period. Besides the time of minimum, also the duration of the constant phase in minimum could be determined for several stars. As these values are poorly known for the stars in question, they are given in the last column (in hours). An asterisk after the star name refers to the remarks. The importance of the observations is demonstrated by the fact that only two stars (AE Cnc and CX Gem) met their GCVS elements satisfactorily. Often the O-C reaches a substantial part of period. A number of stars from the table was occasionally observed visually in the recent years, mainly by the amateur groups B.B.S.A.G. and B.R.N.O. Further minima are, of course, desirable for period improvements. Remarks: CI Aur. Period changes are frequent in this interacting binary. See Borovicka (1993a) for the O-C diagram. The parabolic elements are, however, excluded by the present minimum. MO Aur. The period unknown. Using also of Gessner's (1973) and Borovicka's (1993b) minima, a of period 5.266723 days was derived. An additional image taken at 49 020.258 showed the star near minimum and confirmed the period. The duration of the eclipse is 12 hours. The amplitude in the instrumental system was 12.4-13.4 mag. AN Gem. The formal value of O-C is +0.419 (the period being P = 2.032), but in 1989 the O-C was +0.53 (see Contrib. Brno 30) and is therefore decreasing. It seems probable that O-C in fact exceeds P/2. HI Gem. The normal minimum derived from the observations in 49004 and 49018 is given in Table 1. The elements 47 967.537 + 4.691610 E (Borovicka 1993b) were used for reduction. NN Mon. The formal value of O-C is -0.444 (the period being P = 0.912), but in 1990 the O-C was +-0.44 (see Contrib. Brno 31) and it is therefore clear that O-C just exceeded P/2. Acknowledgments. I am indebted to Mr. P. Pravec for his introducing to CCD photometry. Jirí Borovicka Astronomical Institute 25165 Ondrejov Observatory Czech Republic References: Borovicka J., 1993a, Period study for sixteen eclipsing binaries, Contrib. Obs. Plan. Brno 31, submitted Borovicka J., 1993b, Observation of eclipsing binaries without known period, Contrib. Obs. Plan,. Brno, 31, submitted Gessner H., 1973, Veroff Sternw. Sonneberg, 7, No. 6 Manek J., 1992, Contrib. Obs. Plan. Brno, 30, 30 [BIBCODE 1992CoBrn..30...30M ] Splittgerber E., 1985, Mitt. Verand. Sterne, 10, 153 [BIBCODE 1985MitVS..10..153S ]