COMMISSION 27 OF THE I.A.U. INFORMATION BULLETIN ON VARIABLE STARS Number 2942 Konkoly Observatory Budapest 7 October 1986 HU ISSN 0374 - 0676 PERIOD OF THE ECLIPSING BINARY V382 Cyg Several years ago it was shown (Mayer, 1980) that the measured minima times of the massive O-type binary V382 Cyg fit an ephemeris with a parabolic term, and, except for the two earliest minima, also a linear ephemeris, Some new minima were obtained recently, and they are listed together with the older photoelectric data in Table I. The 65 cm telescope of the Charles University at the Ondrejov Observatory and the 62 cm telescope at the Sarajevo Observatory were used. All the new minima occurred sooner than predicted by the quadratic ephemeris, so that a linear ephemeris is to be preferred. The column O-C_1 in Table I was calculated using the linear ephemeris by Landolt (1975): Pri.Min.= J.D.hel. 2436814.7735 + 1.8855121d E. (1) The up-to-date linear ephemeris presents a little longer period: Pri.Min.= J.D.hel. 2436814.7703 + 1.8855152d E ; (2) the corresponding O-C differences are given in the column O-C_2 and plotted in Fig. 1. Generally, the O-C_2 differences are larger than would correspond to the accuracy of the data, so there should be an unknown factor affecting the minima times. Perhaps a periodic term due to the light-time effect is present. When the ephemeris is changed to Pri.Min.= J.D.hel. 2436814.7703 + 1.8855160d E. (3) (the resulting differences are shown in the column O-C_3), a term with a period of 1375 P - i.e., 7.10 years - and amplitude of about 0.0050 is observed. The value E/1375 (fraction only) is given in the column Phase, and the differences are plotted in Fig. 2. In an abstract published by Bloomer et al. (1979), 18 new minima were mentioned and the following ephemeris was given: Pri.Min. = J.D.hel. 2442940.8071 + 1d.8855143 E. [4) The zero point of this ephemeris corresponds to the epoch E = 3249 according to the other ephemeris presented here. Very probably, the measurements by Bloomer et al. began at the time of this zero point (June 1976) and had to end not later than in about November 1978. Hence, the O-C differences given in Table I were calculated for E = 3475, the expected arithmetical mean of the mentioned time interval, with the "observed" time of minimum following from eq. (4). The time interval June 1976 to November 1978 also corresponds to a limited phase interval of the period 1375 P, see Table I. Therefore, in both graphs the O-C differences could be represented by a horizontal abscissa. As follows from Fig. 2, the minima times by Bloomer et al. lend strong support to the suggested periodic term. In spite of this agreement, the number of measurements is rather low and the periodic term cannot be considered as proven at present. Table I Photoelectric minima times of V382 Cyg J D.hel. 2400000+ m.e. Epoch O-C_1 O-C_2 O-C_3 Phase Note 36814.77247 .001 0 -.0010 +.0022 +.0022 .000 1 38987.8298 .001 1152.5 +.0036 +.0036 +.0023 .838 1 40385.931 .003 1894 -.0024 -.0045 -.0066 .378 1 40386.87609 .0004 1894.5 -.0001 -.0022 -.0043 .378 1 40387.81731 .0011 1895 -.0016 -.0037 -.0058 .378 1 41129.76980 .00022 2288.5 +.0019 -.0013 -.0039 .664 1 42651.3844 .0014 3095.5 +.0082 +.0027 -.0007 .251 2 43366.9333 3475 +.0053 -.0023 -.0051 .36-.69 3 45598.4426 .0007 4658.5 +.0110 +.0011 -.0040 .388 4 46274.3971 .0020 5017 +.0094 -.0015 -.0070 .649 5 46325.3087 .0009 5044 +.0122 +.0012 -.0043 .668 5 46668.4782 .0006 5226 +.0185 +.0070 +.0013 .801 4 Notes: 1 - Landolt (1975); 2 - Mayer (1980); 3 - Bloomer et al. (1979), see text; 4 - this paper (Ondrejov); 5 - this paper (Sarajevo). [FIGURE 1] Figure 1. O-C differences for V382 Cyg according to ephemeris (2). The horizontal line marks the probable time interval and mean O-C for the minima times by Bloomer et al. [FIGURE 2] Figure 2. O-C differences for V382 Cyg according to ephemeris (3), phased with the period of 1375 P. The horizontal line marks the probable phase and mean O-C for the minima times by Bloomer et al. R. MAYER and M. WOLF Department of Astronomy and Astrophysics Charles University, Svedska 8, 150 00 Praha 5, Czechoslovakia M. MUMINOVIC and M. STUPAR Astronomical Observatory M. Tita 44, 71000 Sarajevo, Yugoslavia References: Bloomer, R.H., Burke, E.W., Millis, R.L.: 1979, Bull. Amer. Astron. Soc. 11, 439. [BIBCODE 1979BAAS...11..439B ] Landolt, A.U.: 1975, Publ. Astron. Soc. Pacific 87, 409. [BIBCODE 1975PASP...87..409L ] Mayer, P.: 1980, Bull. Astron. Inst. Czechoslovakia 31, 292. [BIBCODE 1980BAICz..31..292M ]