COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS NUMBER 681 Konkoly Observatory Budapest 1972 May 25 HD 93206 (CSV 6797) AN ECLIPSING SYSTEM PRESENTING OBSERVATIONAL PROBLEMS Discordant observations of Eta Carinae by experienced visual observers led the authors to measure several of the comparison stars during 1971. One of the stars measured, HD 93206, spectral class B0, showed evidence of variability of an unusual nature, in that on every third night the values obtained were almost identical. Other observers have experienced difficulties with this star, but apparently no-one has attempted to confirm either the variability or type. Between 1971 March 24 and 1972 February 3, fifty one photoelectric observations were made at the Auckland Observatory using the 50cm cassegrain reflector, an EMI 9502S/A photomultiplier, and standard UBV filters. On some occasions observations were made in two colours only. The star was observed differentially in relation to HD 93131 whose values were determined as: V=6.50, B-V=-0.03, U-B=-0.80 Stars HD 93943, HD 92964, HD 93737, HD 93695, HD 92740 and HD 92741 were also observed during the programme to ensure non-variability of the main comparison star. The observations show that HD 93206 is an eclipsing binary, possibly of Beta Lyrae type, with a period of almost exactly six days. Both eclipses may be total, although only four observations on three nights have been made near primary eclipse. The observed range in V is from 6.22 to 6.49. The B-V colour remains constant at ~+0.15. Table 1 summarises the observations which have been reduced using the ephemeris: JD 2441030.06 +6.000 E +-0.20+-0.007 These observations are presented graphically in Figure 1. Table 1 Observations of HD 93206 J.D. V B-V U-B Phase 2441000.00 034.91 6.24 0.12 -0.74 0.309 078.91 6.27 0.13 -0.72 0.642 088.84 6.24 0.15 -0.73 0.297 097.76 6.22 0.15 -0.72 0.783 119.76 6.38 0.13 -0.73 0.450 123.77 6.26 0.15 -0.72 0.118 129.78 6.31 0.12 -0.72 0.121 132.77 6.27 0.14 -0.74 0.619 139.80 6.25 0.14 -0.72 0.790 139.89 6.24 0.14 -0.72 0.806 145.77 6.23 0.14 -0.71 0.785 147.78 6.31 0.14 -0.72 0.120 148.83 6.26 0.15 -0.73 0.296 150.77 6.29 0.14 -0.73 0.618 150.79 6.30 0.13 -0.72 0.622 155.84 6.41 0.14 -0.73 0.463 169.82 6.23 0.15 -0.73 0.793 171.79 6.27 0.15 -0.73 0.122 175.81 6.23 0.15 - 0.778 177.79 6.27 0.15 - 0.121 180.79 6.29 0.15 -0.72 0.621 181.90 6.26 0.15 - 0.806 182.80 6.47 0.15 -0.69 0.956 182.83 6.44 0.15 - 0.961 183.80 6.28 0.17 -0.75 0.122 183.81 6.29 0.16 -0.72 0.123 184.80 6.22 0.16 -0.72 0.290 185.79 6.39 0.14 -0.71 0.455 185.80 6.40 0.14 - 0.457 185.92 6.42 0.16 -0.70 0.477 186.79 6.30 0.12 -0.74 0.621 197.80 6.41 0.15 -0.72 0.456 198.18 6.43 0.15 - 0.520 198.81 6.28 0.16 - 0.625 209.80 6.38 0.13 -0.75 0.456 258.10 6.44 0.16 -0.71 0.507 259.03 6.29 0.16 - 0.662 264.97 6.28 0.16 - 0.651 268.06 6.29 0.14 - 0.167 269.14 6.26 0.13 - 0.347 290.96 6.49 0.15 - 0.983 296.05 6.29 0.14 - 0.831 303.05 6.47 0.15 - 0.999 341.93 6.43 0.15 - 0.479 341.95 6.44 0.15 - 0.481 342.02 6.43 0.14 - 0.493 342.09 6.42 0.16 - 0.504 342.96 6.28 0.14 - 0.651 348.94 6.25 0.14 - 0.647 349.02 6.25 0.14 - 0.660 349.96 6.27 0.16 - 0.817 350.95 6.47 0.14 - 0.982 [FIGURE 1] Figure: HD 93206 photoelectric observations as listed in Table 1 Using these elements the observations do not show any significant change in phase over 300 days. Both eclipses appear to be of relatively long duration and we have not been able to observe the egress from totality, although it appears that the ingress of the secondary eclipse is being observed. The period of this system, and the relatively small amplitude of the light variations, is such that the determination of an accurate epoch and period has proved impossible; nor has it been possible to fill the large gaps in the light curve. The solution to these problems probably lies in joint observations by several suitably located observers. As this star is not of a type normally observed in Auckland we do not plan any further observations other than in conjuction with our study of the light variations in Eta Carinae. We are thus presenting the somewhat incomplete observations of this star in the hope that others may be encouraged to attempt observations. 1972 February, 13 (revised 1972 May) W.S.G. WALKER BRIAN F. MARINO Auckland Observatory, of the Auckland Astronomical Society, Auckland, New Zealand.