COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 3527 Konkoly Observatory Budapest 16 October 1990 HU ISSN 0374 - 0676 NEW PHOTOELECTRIC MINIMA TIMES OF TZ DRACONIS AND ITS PERIOD STUDY The eclipsing binary star TZ Dra (BD +47d 2625 (Faulkner, 1986)) has been observed photoelectrically from the National Observatory of Athens, Greece, during 1983. The observations were made using a two-beam, multi-mode, nebular-stellar photometer attached to the 48-inches Cassegrain reflector at the Kryonerion Astronomical Station. The stars HD 170074 (of mv=9.0) and HD 170357 (of mv=8.31) were used for comparison and checking, respectively. The two intermediate pass bands of the filters used are in close accordance to the international UBV system and the photometer was cooled using dry ice. Reduction of the observations has been made (Hardie, 1962) as usual. From our observations 4 new minima times (three primaries and one secondary) were derived. They were found using Kwee and Van Woerden's method (1956) and are the mean values of our B and V observations. They are presented in Table I the successive columns of which give: the Hel. JD; the residuals (O-C)_I, (O-C)_II and (O-C)_III; and the corresponding number of cycles passed, E_I, E_II and E_III. The C's have been calculated using the three different proposed ephemeris formulae for TZ Draconis, which are: Min I= 2433871.389 + 0.8660337d E (I) (due to Perova, 1952) Min I= 2437911.4347 + 0.8660333d E (II) (due to Plavec, 1964) Min I= 2442966.482 + 0.8660347d E (III) (Kholopov et al., 1985) [FIGURE 1] Figure 1 The O-C diagram of TZ Dra based on primary minima times only and according to Kholopov's et al. (1985) ephemeris formula. (Notations: Open circles (o) represent the photographic minima times, crosses (+) the photoelectric and filled circles ([filled circle]) the visual ones. TABLE I (New Photoelectric Minima Times of TZ Draconis) Hel. JD (O-C)_I E_I (O-C)_II E_II (O-C)_III E_III 2440000.+ days days days 5488.3792 .0141 13414 .0192 8749 .0042 2912 5495.3097 .0164 13422 .0214 8757 .0064 2920 5497.4786 .0202 13424.5 .0252 8759.5 .0102 2922.5 5585.3717 .0109 13526 .0159 8861 .0008 3024 From all the minima times of TZ Dra found in the literature, Table II was made, in which the (O-C) values have been calculated using Kholopov's et al. (1985) ephemeris formula. Using the data of Tables I and II, the figure 1 was drown, which represents the O-C diagram of TZ Draconis, in which crosses denote the photoelectric minima times, open circles the photographic and filled circles the visual ones. From the data of Table I only the three primaries have been taken into account, since the system appears to have an eccentric orbit. As one can see from Figure 1, a linear least square fitting to all the data shows a small change in the period of TZ Dra, but since almost all the minima times (with the exception of the first two and some visual) lay around zero this must not be true. TABLE II Minima Times of TZ Draconis (According to Kholopov's et al. ephemeris formula) Hel. JD (O-C)_III E_III Obs. Reference 2400000.+ days Kind 17445.332 0.027 -29469 pg Plavec, 1964 30588.272 -0.024 -14293 pg " 3852.339 0.006 -10524 pg " 3864.460 0.003 -10510 v " 3865.320 -0.003 -10509 v " 3871.390 0.005 -10502 v " 3884.367 -0.009 -10487 pg " 3950.196 0.001 -6024 pg " 7840.4202 -0.0024 -5919 pe " 7866.3999 -0.0038 -5889 pe " 7897.5771 -0.0038 -5853 pe " 7905.3730 -0.0022 -5844 pe " 7911.4342 -0.0033 -5837 pe " 7911.4353 -0.0022 -5837 pe " 40394.353 -0.006 -2970 pe Pohl et al., 1970 0419.4667 -0.0072 -2941 pe " 0814.3824 -0.0034 -2485 pe Kizilirmak et al., 1971 0852.492 0.001 -2441 pe " 1519.3351 0.0029 -1671 pe Kizilirmak et al., 1974 2966.4820 0.0000 0 pe Pohl et al., 1977 4770.4300 -0.0023 2083 v BBSAG No. 55, 1981 5223.3430 -0.0254 2606 v BBSAG No. 62, 1982 5275.3290 -0.0015 2666 v BBSAG No. 64, 1983 5478.8447 -0.0040 2901 pe Faulkner, 1986 6335.314 -0.016 3890 v BBSAG No. 78, 1985 6657.523 0.002 4262 v BBSAG No. 81, 1986 6962.349 -0.015 4614 v BBSAG No. 84, 1987 6981.411 -0.008 4636 v " 7000.469 -0.003 4658 v BBSAG No. 86, 1988 7324.372 0.003 5032 v BBSAG No. 88, 1988 7330.424 -0.007 5039 v BBSAG No. 89, 1988 7362.474 0.000 5076 v " 7369.404 0.002 2084 v " 7382.377 -0.016 5099 v " 7467.276 0.012 5197 v BBSAG No. 90, 1989 7480.247 -0.008 5212 v " 7757.373 -0.003 5532 v BBSAG No. 91, 1989 7770.372 -0.004 5547 v " 7816.275 -0.001 5600 v BBSAG No. 93, 1990 H. ROVITHIS-LIVANIOU P. ROVITHIS Section of Astrophysics Astronomical Institute Astronomy and Mechanics National Observatory of Athens University Athens, P.O. Box 20048 GR 157 83 Zografos, Athens, Greece Athens 118 10, Greece References: Faulkner, D.R.: 1986, Publ. Astron. Soc. Pacific 98, 690. [BIBCODE 1986PASP...98..690F ] Hardie, R.H.: 1962, in W.A. Hiltner (ed.), Stars and Stellar Systems Vol. II, Astronomical Techniques. The University of Chicago Press, Chicago. Kholopov, P.N. et al.: 1985, Fourth Edition of the General Catalogue of Variable Stars, Moscow. Kizilirmak, A. and Pohl, E.: 1971, I.B.V.S. No. 530. Kizilirmak, A. and Pohl, E.: 1974, I.B.V.S. No. 937. Kwee, K.K. and Van Woerden, H.: 1956, Bull. Astron. Inst. Neth. 12, 327. [BIBCODE 1956BAN....12..327K ] Perova, N. B.: 1952, Peremennyje Zvezdy 9, 142. Plavec, M.: 1964, Bull. Astron. Inst. Ch. 15, 23. [BIBCODE 1964BAICz..15...23P ] Pohl, E. and Kizilirmak, A.: 1970, I.B.V.S. No. 456. Pohl, E. and Kizilirmak, A.: 1977, I.B.V.S. No. 1358.