COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 941 Konkoly Observatory Budapest 1974 October 29 IMPROVED LIGHT ELEMENTS FOR THE ECLIPSING BINARIES RZ Cha, YZ Cha AND DZ Mus Photoelectric UBV observations of these three stars have been carried out with the 50 cm photometric reflector of the European Southern Observatory by one of the authors (E.G.). The observed minima lead to a revision of the published light elements. RZ Cha = BV 473. With the elements given by Strohmeier, Knigge and Ott in IBVS No. 66. 1964 no predicted minima during the observational period J.D.2442139 to 2442152 could be observed. By chance a minimum tip and the following light rise to maximum was catched. The period is slightly longer by 0d.0037. A weighted least square solution of the minima of Table 1 yields the following elements: Min = J.D.hel. 2438439.410 + 2d.832093.E +-.002 +-.000061 The mean dispersion of the (O-C) in Table 1 is +-0d.038. The light curve is of EA-type with a deep secondary minimum. YZ Cha = BV 704. No trace of a secondary minimum of this EA-type eclipser was observed predicted by the light elements given by Strohmeier in IBVS No. 184, 1967, though the two completely covered pe-minima are in accordance with these. Since they are extremely wide, and slightly different in depth by less than 0m.05 the period has to be doubled. A weighted least square solution of the minima of Table 2 gives the following elements with a mean dispersion of +-0d.031 for (O-C): Min I = J.D.hel. 2428820.613 + 4d.457357.E +-.002 + +-.000184 Min I is shallower than Min II. This double star system consists therefore of nearly equal components, similar to EI Cep or PV Cas. DZ Mus = BV 1209 The two observed pe-minima show a slight phase displacement to the published light elements by Strohmeier and Patterson in IBVS No 330, 1969. This demands a slightly longer period. The weighted least square solution of the minima of Table 3 gives the light elements: Min = J.D.hel. 2418093.728 + 3d.247619.E +-.002 +-.000091 The (O-C) of Table 3 show a mean dispersion of +-0d.028. The absence of a noticable secondary minimum and the fairly large width of the photoelectrically observed minima would also favour the doubling of the period of this EA-system. A decision is perhaps only possible by spectrographic observations. Table 1 : RZ Cha Minima E O-C Minima E O-C 243 8439.402 0 - 0.008 243 9181.375 262 - 0.044 .446 0 + 0.036 .421 262 + 0.002 .492 0 + 0.082 .471 262 + 0.052 8473.335 12 - 0.060 9235.230 281 + 0.002 .378 12 - 0.017 9259.267 289.5 - 0.034 .423 12 + 0.028 9269.238 293 + 0.024 8500.263 21.5 - 0.037 9535.403 387 - 0.027 .307 21.5 + 0.007 .450 387 + 0.020 .352 21.5 + 0.052 9562.303 396.5 - 0.032 8817.449 133.5 - 0.046 .349 396.5 + 0.014 .494 133.5 - 0.001 .396 396.5 + 0.061 8827.362 137 - 0.045 244 0026.802 560.5 + 0.004 8878.311 155 - 0.074 0629.996 773.5 - 0.038 8915.208 168 + 0.006 0630.045 773.5 + 0.011 2146.620(pe) 1309 0.000 Table 2 : YZ Cha Minima E O-C Minima E O-C 242 8820.623 (S) 0 - 0.009 243 8914.254 2264.5 - 0.045 8878.553 (S) 13 - 0.006 9179.458: 2324 - 0.053 243 8524.254 2177 - 0.026 .503 2324 - 0.008 .299 2177 + 0.019 .549 2324 + 0.038 8553.199 2183.5 - 0.052 9197.344 2328 + 0.003 .242 2183.5 - 0.011 9235.275 2336.5 + 0.047 8562.201 2185.5 + 0.034 9972.889 2502 - 0.032 8760.556 2230 + 0.036 244 0712.842 2668 + 0.000 8818.446 2243 - 0.021 .887 2668 + 0.045 .492 2243 + 0.027 1064.938 2747 - 0.035 8827.362 2245 - 0.018 .986 2747 + 0.013 8885.266: 2258 - 0.060 1093.910 2753.5 - 0.036 .312 2258 - 0.014 2143.655(pe) 2989 0.000 .359 2258 + 0.033 2145.881(pe) 2989.5 0.000 Remarks: (S) = Minima from Sonneberg plate collection. Table 3 : DZ Mus Minima E O-C Minima E O-C 241 8093.736 (H) 0 + 0.008 243 4315.597(S) 4995 + 0.012 9509.675 (H) 436 - 0.015 4419.434(S) 5027 - 0.075 242 1331.585 (H) 997 - 0.019 8206.220 6193 - 0.012 8710.211 (H)3269 + 0.016 8521.257 6290 - 0.001 9382.482 (H)3476 + 0.030 .296 6290 + 0.044 Table 3 : DZ Mus (continued) Minima E O-C Minima E O-C 243 8547.198 6298 - 0.034 243 9268.214 6520 + 0.014 .242 6298 + 0.010 9294.208 6528 + 0.023 8560.198 6302 - 0.025 9972.889 6737 - 0.048 .242 6302 + 0.019 .934 6737 - 0.003 8901.213 6407 - 0.010 9998.872 6745 - 0.046 .258 6407 + 0.035 .917 6745 - 0.001 8914.208 6411 - 0.005 244 1099.890 7084 + 0.029 .254 6411 + 0.041 2145.596(pe) 7406 - 0.002 2148.840(pe) 7407 + 0.002 Remarks: (H) = Minima from Harvard plate collection (S) = Minima from Sonneberg E.H. GEYER R. KNIGGE Astron. Institut der Remeis-Sternwarte Bamberg Universitat Bonn Astron. Institut der Universitat Observatorium Hoher List Erlangen-Nurnberg