COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 2637 Konkoly Observatory Budapest 5 December 1984 HU ISSN 0374 - 0676 UBV LIGHT VARIATION OF THE WR STAR HDE 311884 The double-lined spectroscopic binary HDE 311884=MR 42. (2000.0 RA:12h43m 50.6s, DEC:-63d5.3') (Roberts, 1962) is a southern WR star of spectral type WN6+0 (Smith, 1968) probably associated with the open cluster Hogg 15 (Moffat 1974). It is a very massive system with minimum masses around 40 M_sun for the WN6 component and 47 M_sun for the unevolved early-type O companion (Niemela et al., 1980). In that work it was strongly urged that MR 42 be observed photoelectrically, so it was included among others, in a photoelectric broad band observing program designed to detect or confirm light variations in WR systems. The purpose of the present paper is to report differential observations of HDE 311884 taken at CTIO in an 11 day observing run showing a light variation. In 1981 the differential observations were done between August 15 and August 26 with the 61 cm Lowell telescope at CTIO. A standard one-channel photometer was used together with conventional UBV filters and refrigerated photomultiplier RCA 1P21. Three stars were used as comparison stars. They were selected close in the sky to MR 42 (about 3') and also close in the colors from previous absolute UBV photoelectric photometry of stars near and in Hogg 15 (Feinstein and Marraco, 1971, Moffat, op. cit., Muzzio et al., 1976 ). The comparison stars C1, C2 and C4 were numbered identically with those beginning with H in the work of Feinstein and Marraco (op. cit.). Each daily observation cycle consisted of the sequence C1 - C2 - C4 - WR - WR - C4 - C2 - C1. Each observation of the cycle was made in the typical symmetrical pattern V-B-U-U-B-V together with the associated sky background The interval of time required for observing the whole cycle was about 40 minutes. A diaphragm of about 15" was used The sky measures were made as close as possible to the stars and every time in the same place. The hour angle of the observations was about 4 hours west. The data reduction process has been made both including and not including the first and second order extinction coefficients. The results never differed more than 0.005m. After subtracting the sky background the star counts were converted into magnitudes. The magnitudes were interpolated to [FIGURE 1] Figure 1 Differential observations of MR 42. Triangles, crosses and circles represent magnitude differences in V, B and U, respectively. Table I Differential Observations ----------------------------------------------------------------------- JD (Hel.) Deltav Deltab Deltau Deltab-Deltav Deltau-Deltab 2440000+ ----------------------------------------------------------------------- WR-C4 4831.5114 -1.484 -1.702 -1.790 -0.218 -0.088 4831.5152 -1.486 -1.723 -1.821 -0.237 -0.098 4833.5150 -1.525 -1.745 -1.811 -0.220 -0.065 4833.5190 -1.521 -1.755 -1.811 -0.235 -0.056 4834.9959 -1.458 -1.656 -1.679 -0.198 -0.023 4834.9997 -1.461 -1.641 -1.657 -0.180 -0.016 4837.4874 -1.481 -1.692 -1.680 -0.211 0.012 4837.4912 -1.491 -1.699 -1.659 -0.208 0.040 4839.4910 -1.513 -1.751 -1.778 -0.238 -0.027 4839.4945 -1.537 -1.763 -1.781 -0.226 -0.018 4842.4949 -1.459 -1.651 -1.673 -0.191 -0.023 4842.4989 -1.421 -1.629 -1.662 -0.208 -0.033 WR-C2 4831.5114 -1.391 -1.473 -1.512 -0.082 -0.040 4831.5152 -1.394 -1.493 -1.542 -0.099 -0.050 4833.5150 -1.445 -1.494 -1.540 -0.048 -0.047 4833.5190 -1.446 -1.510 -1.568 -0.064 -0.058 4835.4959 -1.373 -1.427 -1.469 -0.055 -0.042 4835.4997 -1.379 -1.427 -1.459 -0.048 -0.032 4837.4874 -1.394 -1.443 -1.468 -0.049 -0.025 4837.4912 -1.409 -1.454 -1.464 -0.045 -0.010 4839.4910 -1.435 -1.499 -1.530 -0.064 -0.030 4839.4945 -1.447 -1.503 -1.521 -0.056 -0.018 4842.4949 -1.391 -1.460 -1.438 -0.069 0.021 4842.4989 -1.360 -1.438 -1.451 -0.077 -0.013 C4-C2 4831.5075 0.095 0.227 0.276 0.133 0.049 4831.5179 0.093 0.228 0.279 0.135 0.051 4833.5109 0.086 0.258 0.301 0.172 0.042 4833.5216 0.073 0.241 0.228 0.168 -0.013 4835.4919 0.091 0.239 0.216 0.148 -0.024 4835.5027 0.079 0·208 0.196 0.129 -0.012 4837.4834 0.086 0.248 0.237 0.162 -0.011 4837.4938 0.085 0.247 0.223 0.162 -0.024 4839.4871 0.070 0.246 0.230 0.176 -0.016 4839.4970 0.095 0.264 0.276 0.168 0.012 4842.4908 0.067 0.196 0.263 0.129 0.067 4842.5014 0.066 0.187 0.195 0.121 0.008 C4-C1 4831.5075 0.262 0.315 0.305 0.053 -0.010 4831.5179 0.277 0.339 0.387 0.062 0.048 4833.5109 0.124 0.218 0.266 0.093 0.048 4833.5216 0.197 0.250 0.225 0.053 -0.024 4835.4919 0.294 0.321 0.373 0.026 0.052 4835.5027 0.268 0.280 0.313 0.012 0.033 4837.4834 0.274 0.306 0.328 0.032 0.022 4837.4938 0.269 0.297 0.306 0.027 0.009 4339.4871 0.277 0.328 0.350 0.051 0.022 4839.4970 0.297 0.344 0.379 0.047 0.035 4842.4908 0.303 0.353 0.363 0.050 0.011 4842.5014 0.264 0.288 0.319 0.024 0.031 perform the following differences; WR-C4, WR-C2 C4-C2 and C4-C1. These values are listed in Table I. The daily mean values are displayed in Figure 1. The differences C4-C2 show a dispersion typical of that folded in the light curves when observations of different days are grouped together in phase, though the dispersion in the U band is somewhat greater than expected, possibly due to the small number of the total star counts in that light (6000). On the contrary, the differences WR-C4 do establish a scatter that is three and two times greater than the normal dispersion in V, and B,U light,respectively. The differences WR-C2 are identical with the previous ones in the V band, while for B and U light are somewhat smaller, possibly due to the fact that comparison 2 is embedded in Hogg 15. The differences C4-C1 (not included in the figure) confirm the light variation of comparison 1 announced by Moffat (op. cit.) and Muzzio et al. (op. cit. ). It is concluded therefore, that MR 42 shows light variations with an amplitude about 0.1m in UBV light. The trend of the photometric observations also suggests a possible orbital period of the system between 6 and 7 days which agrees with the value 6.34d found from the velocity curves (Niemela et al., op. cit.). New photometric observations are needed to determine the shape of the light curve and to estimate the inclination of this very massive system. MIGUEL ANGEL CERRUTI* Instituto de Astronomia y Fisica del Espacio CC 67 Suc. 28 1428 Buenos Aires, Argentina * Visiting astronomer, Cerro Tololo Inter-American Observatory, supported by the National Science Foundation under Contract No. AST 78-27879 References: Feinstein, A. and Marraco, H.G. 1971, Pub.Astr.Soc.Pacific Vol. 83, 218. [BIBCODE 1971PASP...83..218F ] Moffat, A.F. 1974, Astr.Ap. 34, 29. [BIBCODE 1974A&A....34...29M ] Muzzio, J.C., Feinstein, A. and Orsatti, A.M. 1976, Pub.Astr.Soc.Pacific Vol. 88, 526. [BIBCODE 1976PASP...88..526M ] Niemela, V.S., Conti, P.S. and Massey, P. 1980, Astrophys. J. Vol. 241, 1050. [BIBCODE 1980ApJ...241.1050N ] Roberts, M.S. 1962, Astron. J., Vol. 67, 79. [BIBCODE 1962AJ.....67...79R ] Smith, L.F. 1968, Mon. Not. R.A.S, Vol. 138, 109. [BIBCODE 1968MNRAS.138..109S ]