COMMISSION 27 OF THE I.A.U. INFORMATION BULLETIN ON VARIABLE STARS Number 2965 Konkoly Observatory Budapest 15 December 1986 HU ISSN 0374 - 0676 PHOTOELECTRIC OBSERVATIONS OF Theta CrB IN 1984-86 The Be-star Theta CrB was included on our observational programme in mid 1984 after Harmanec's (1983) predicted time of possible eclipse. The three colour UBV photoelectric observations of Theta CrB presented in this paper were performed at the University Observatory in Brno in the course of the years 1984-86. The photomultiplier and filter combinations on a one-channel photoelectric photometer attached to the 24-inch telescope were the same as in Papousek (1974). The instrumental photometric system was close to the standard UBV system and the transformations from the instrumental system to the UBV one and the differential extinction corrections were applied to all the observations in the usual way. HR 5760 (= HD 138341) served as a primary comparison star, the stars 50 Boo and BD +32d2607 (= SAO 64824) were used as check stars. Their brightness and colour indices - as observed by us - are given in Table I. Table I Photometric data for comparison and check stars Star V B-V U-B HR 5760= comparison 6.440 +0.188 +0.126 +-2 +-3 +-4 50 Boo = check 1 5.368 -0.065 -0.210 +-1 +-3 +-2 BD +32d2607= check 2 7.205 +0.228 +0.095 +-4 +-3 +-5 The photometric values of 50 Boo were derived from the observations of 16 standard stars in the neighbourhood of Theta CrB during three nights. The values of HR 5760 were derived from differential observations to the 50 Boo in 38 nights in 1985-86 and scattering of individual measurements did not exceed +-0.015 in V, +-0.020 in B, and +-0.025 in U colour, respectively. Data for check star 2 were computed from differential observations to the comparison star and to 50 Boo in 41 nights and scattering of its values is similar as for HR 5760. The variable star Theta CrB was observed in 57 nights, between 22.5.1984 and 4.10.1986 and about 1300 individual measurements were obtained. These observations in different nights are presented in Table II, where phases are computed according to the ephemeris given in Harmanec (1983), : denotes less accurate measurements and n in the last column denotes the number of individual observations. Table II Photometric observations of Theta CrB JD-2440000 Phase V B U n 5843.347 0.974 4.155 4.021 3.502 12 +-5 +-35 +-40 .385 4.121 -- -- 6 9 5851.365 0.990 4.132 4.016 3.456 36 11 7 16 .472 4.068: 3.909: 3.424: 11 11 25 80 5853.354 0.994 4.151 -- 3.501 13 16 11 .44 4.158 4.016 3.450 12 14 8 1 5858.403 0.003 4.097 4.025 3.478 19 5 7 6 5879.382 0.044 - 4.016 3.465 14 4 10 5940.317 0.164 4.209 -- -- 6 20 5941.326 0.166 4.132 4.017 3.467 20 6 7 3 6176.443 0.626 4.136 4.022 3.466 21 4 2 2 6177.429 0.628 4.120 4.016 3.460 24 3 2 4 6178.431 0.630 4.137 4.013 3.455 23 3 2 3 6182.388 0.638 4.174: 4.004 3.478: 15 3 8 21 6194.498 0.661 4.144 4.004 3.461 15 3 4 4 6197.390 0.667 4.141 4.012 3.453 25 4 5 9 6210.444 0.693 4.127 4.009 3.464 20 2 2 4 6212.424 0.696 4.122 4.012 3.455 24 4 7 4 6221.417 0.714 4.136 4.021 3.458 42 1 2 6 6224.384 0.720 4.135 4.017 3.466 17 1 2 2 6244.363 0.759 4.132 4.013 - 10 4 9 6247.374 0.765 4.134 4.011 3.458 34 5 2 7 6249.378 0.769 4.141 4.023 3.453 36 2 3 4 6251.377 0.773 4.127 4.025 3.458 38 2 2 8 6253.382 0.777 4.140 4.015 3.483 20 1 2 9 6280.344 0.829 4.131 4.018 3.458 33 2 4 7 6290.333 0.849 4.134 4.029 3.469 38 1 3 6 6292.339 0.853 4.132 4.030 3.499: 23 1 7 14 6293.326 0.855 4.140 4.042 3.482 34 3 4 7 6297.331 0.863 4.137 4.004 3.448 30 9 5 8 6299.311 0.866 4.155 4.042 3.484: 18 4 4 6300.313 0.868 4.111 4.037 3.503 38 6 8 3 6308.322 0.884 4.146 4.023 3.455 25 5 12 7 6309.299 0.886 4.134 4.026 3.469 27 7 8 6 6311.299 0.890 4.129 4.029 3.463 36 3 4 3 6318.293 0.904 4.140 4.009 3.460 17 4 13 7 6327.326 0.921 4.160 4.038 3.481 27 7 3 6 6328.271 0.923 4.147 4.015 3.454 22 6 2 15 6334.257 0.935 4.137 4.028 3.479 29 5 4 4 6338.258 0.943 4.128 4.021 3.481 24 2 2 4 6340.264 0.947 4.127 4.028 3.482 21 3 5 5 6343.250 0.952 4.149 4.027 3.483 23 14 3 4 6363.214 0.992 4.156 4.057 -- 9 14 8 6592.417 0.440 4.130 4.018 3.461 20 1 6 4 6605.388 0.466 4.130 4.004 3.467 23 7 2 2 6607.396 0.469 4.129 4.008 3.444 21 10 4 4 6609.384 0.473 40096 4.006 3.462 22 10 15 7 6612.363 0.479 4.138 4.023 3.452 12 3 6 4 6614.382 0.483 4.105 4.000 3.465 22 6 2 2 6626.370 0.507 4.148 4.019 3.467 19 5 8 6 6646.361 0.546 4.140 4.017 3.441 17 5 5 4 6660.313 0.575 4.181 4.019 3.472 29 7 6 8 6672.299 0.599 4.142 -- -- 3 13 6679.297 0.610 4.129: 4.029 3.481 12 27 15 10 6685.303 0.622 4.116 4.009 3.469 19 3 5 7 6690.282 0.632 4.130 4.016 3.464 23 6 9 5 6693.309 0.638 4.158 4.043: 3.494 9 7 44 10 6700.267 0.651 4.138 4.029 3.453 19 15 9 23 6705.250 0.661 4.138 4.036 3.510: 12 20 15 25 6708.250 0.667 4.139 4.037 3.444 12 15 5 12 The averaged photometric values of Theta CrB in different years are collected in Table III. Table III Averaged photometric values of Theta CrB in 1984-86 Year V B-V U-B nights 1984 4.135 +-.008 -0.120 +-.006 -0.550 +-.007 8 1985 4.136 +-.002 -0.115 +-.002 -0.555 +-.002 33 1986 4.130 +-.004 -0.110 +-.003 -0.555 +-.004 17 From the measurements listed in the Table II it is clear that no decline of brightness of Theta CrB exceeded 0.06 mag in each colour was observed in 1984-86. Some different declines occurring in V and U colours in different heights are very similar to that observed by Fernandes et al. (1985) on July 22, 1984. Small changes in brightness of Theta CrB from night to night are - in our opinion - real and we agree with the result of Fernandes et al. that the eclipse of this hypothetical binary system in the interval of our observations did not occur. J. PAPOUSEK Department of Astronomy Brno University Kotlarska 2 611 37 Brno, CSSR References: Fernandes, M., Kamper, B.-C., and Nelles, B. 1985, Inf.Bull.Var.Stars No. 2801. Harmanec, P.,: 1983, Bull.Astr. Inst. Czech. 34, 324. [BIBCODE 1983BAICz..34..324H ] Papousek, J.,: 1974, Bull.Astr. Inst. Czech. 25, 152. [BIBCODE 1974BAICz..25..152P ]