COMMISSIONS 27 AND 42 OF THE IAU INFORMATION BULLETIN ON VARIABLE STARS Number 3960 Konkoly Observatory Budapest 8 December 1993 HU ISSN 0374 - 0676 THE PERIOD AND LIGHT CURVE OF V1028 ORI The variability of V 1028 Ori (HDE 255930, BD +10d 1104) was discovered by Turner (1976a) during a study of OB stars in Northern Monoceros. From these first observations the star was classified as a beta Lyrae type eclipsing variable with an estimated period of 3 days. Additional photoelectric UBV observations of V1028 Ori were obtained by AMH in 1975-1978 during several observing runs at Kitt Peak National Observatory. The variable was measured differentially with respect to HD 46223 on 11 nights and with respect to HD 43526 on 17 nights; however, the final differential values were all adjusted to HD 46233. The differential data have been corrected for atmospheric extinction and transformed to the UBV system via observations of Praesepe standard stars. The errors in these KPNO differential observations range from about +-0.002 to +-0.007 mag in V, +-0.003 to +-0.010 mag in B-V, and +-0.004 to +-0.013 mag in U-B. The new UBV observations are presented in Table 1. Values of V = 7.28, B-V = +0.22 and U-B = -0.78 for HD 46223 (Heiser 1977) were used to obtain the magnitudes and colours from the differential data. The analysis of variance technique (Schwarzenberg-Czerny 1989) was applied to the data to determine a more accurate value for the period of the system. The new ephemeris for V 1028 Ori is: JD Hel Min I = 2442359.659 + 3.011428 x E. +-1 +-3 The V, B-V and U-B light curves for V 1028 Ori are presented in Figure 1. The observations of Turner (1976a) are marked by open circles and those from Table 1 by filled circles. The discordance of a few of the original observations by Turner (crosses) from the mean light curve can be attributed to problems arising from incomplete corrections for a seasonal dust extinction component (due to nearby open pit mining) which can affect the skies over Cerro Las Campanas in Chile. Table 1. New UBV photoelectric photometry for V 1028 Ori ---------------------------------------------------------------------- JD Hel JD Hel 2443000+ V B-V U-B 2443000+ V B-V U-B ---------------------------------------------------------------------- 102.0049 9.874 0.111 -0.605 224.6398 9.753 0.113 -0.581 102.9665 9.779 0.121 -0.586 225.6377 9.851 0.124 -0.622 103.8616 9.814 0.117 -0.593 226.6379 9.841 0.132 -0.585 104.8891 9.848 0.121 -0.622 482.8743 9.916 0.114 -0.574 105.9334 9.774 0.112 -0.575 483.8814 9.747 0.119 -0.602 106.9548 9.802 0.111 -0.593 484.8882 9.779 0.123 -0.612 107.9130 9.852 0.119 -0.618 485.8814 9.924 0.111 -0.582 108.8823 9.751 0.126 -0.594 488.8854 9.921 0.118 -0.567 127.8092 9.848 0.119 -0.589 489.8692 9.749 0.118 -0.598 128.8400 9.814 0.129 -0.611 602.6434 9.738 0.121 -0.586 156.8316 9.749 0.123 -0.588 603.6454 9.848 0.113 -0.594 157.7190 9.930 0.126 -0.583 604.6431 9.822 0.119 -0.605 158.7250 9.766 0.100 -0.596 605.6479 9.745 0.128 -0.582 222.6475 9.841 0.126 -0.603 609.6507 9.859 0.095 -0.572 . The shape of the light curve, the period and the spectral type of B2 IV (Turner 1976b) all confirm the original classification of V 1028 Ori as a beta Lyrae type system. The system undergoes partial eclipses, and the amplitude of the brightness variation is relatively small: 0.19 magnitude in V. The parameters for the light curve of V 1028 Ori are summarized in Table 2. Table 2. Parameters for the light curve of V 1028 Ori ------------------------------------------------------------- V_max = 9.74 (U-B)_min = -0.62 (at secondary eclipse) V_min I = 9.93 (U-B)_max = -0.58 (at primary eclipse) V_min II = 9.86 = 0.12 ------------------------------------------------------------- The amplitude of the U-B light curve is only 0.04 mag; nevertheless it exhibits a pronounced maximum at secondary eclipse and a minimum at primary eclipse, which indicates that the secondary is of later spectral type than the primary. The B-V colour index, on the other hand, does not appear to pass through obvious maxima or minima throughout the cycle; it varies about a mean = 0.12, with a dispersion of ~0.01 magnitude. This difference can be explained by the stronger dependence of the U-B index on temperature for early spectral types. [FIGURE 1] Figure 1. V, U-B and B-V light curves for V1028 Ori The original classification spectrogram for this star was the basis for its assigned spectral type of B2 IV, although there was some suggestion of diffuseness in the spectral lines which might arise from rotation or mild line doubling. This was not sufficient to warrant a classification of B2 IVn for the variable, but, in the light of the star's duplicity, this should be investigated further with higher dispersion spectra. Because of the somewhat uneven phase coverage, we did not attempt to construct a complete model of the binary. Rough estimates of the properties of the system show an overall consistency between the observed and derived parameters, even though the estimated separation of the stars in this system, based on their likely masses and the orbital period, is only slightly larger than the calculated dimensions of a subgiant B2 star. AMH wishes to thank the Director of KPNO for granting observing time with the No. 3 and No. 416-inch telescopes. Georgi I. MANDUSHEV Department of Astronomy & Physics Saint Mary s University Halifax, Nova Scotia B3H 3C3 Canada Arnold M. HEISER David G. TURNER Dyer Observatory Dept. of Astronomy & Physics Box 1803, Vanderbilt University Saint Mary s University Nashville, Tennessee 37235 Halifax, Nova Scotia B3H 3C3 USA Canada References: Heiser, A. M., 1977, AJ, 82, 973 [BIBCODE 1977AJ.....82..973H ] Schwarzenberg-Czerny, A., 1989, MNRAS, 241, 153 [BIBCODE 1989MNRAS.241..153S ] Turner, D. G., 1976a, IAU IBVS, No. 1166 Turner, D. G., 1976b, ApJ, 210, 65 [BIBCODE 1976ApJ...210...65T ]