COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 2801 Konkoly Observatory Budapest 1 October 1985 HU ISSN 0374 - 0676 OBSERVATIONS OF THETA CORONAE BOREALIS IN SUMMER 1984 (BAV-Mitteilungen Nr.41) Harmanec (1983) suspected the Be star Theta CrB to be a long-periodic spectroscopic binary with an orbital period of 510.87 days. The predicted time of a hypothetical primary eclipse from the orbital solution was found to coincide remarkably well with the 0.7m deep photometric minimum observed by Roark (1971). The next primary eclipse was expected to occur on May 25 - June 15, 1984. Here we present photometric and spectroscopic observations obtained during May, June and July 1984. M. Fernandes observed with a 10 inch Schmidt-Cassegrain and a Schnitzer type photometer furnished with an (uncooled) EMI 9781B tube and filters for B and V. At the same time, spectrograms of Theta CrB were obtained with the Universal-Astro grating spectrograph at the 106 cm Cassegrain of the Hoher List Observatory (dispersion: 32.5 A/mm, projected slit dimensions: 0.014 x 0.28 mm, wavelength range: lambda lambda 3700-4800, emulsion:IIaO). The photometric data are shown in Table I. Primary comparison star was Eta CrB while HD 138341 served as check star. The mean magnitude difference (in the sense 'Comp minus Check') was found to be -1.15m in B, and -1.46m in V, with no significant variations. The standard deviation of a single differential magnitude, corrected for atmospheric extinction and transformed to the standard system, is +- 0.015m. Assuming (V = 4.98, B-V = 0.58) for Eta CrB (Nicolet 1978), we get B = 4.04, V = 4.13 and B-V = -0. 09 for Theta CrB, in the interval JD 2445844...879. We may state that the star has remained constant within a few hundredth mag during this time. In July, a mild blueing occurred whereupon the star became slightly fainter. No check star observations were made at these dates, but on July 22, Theta CrB was additionally compared with Upsilon CrB (V= 5.78, B-V= +0.07), Phi Boo (V= 5.24, B-V= +0.88), and HR 5741 (V= 5.46, B-V= +1.40) (Nicolet 1978), resulting in V = 4.20, B-V = -0.11. It is improbable that we should have missed the eclipse since its duration should be some 10 to 13 days. So presumably there was none. Radial velocity data are presented in Table II. All measurements were made on a computer supported Abbe comparator with oscilloscopic setting at OHL. Table I Var minus Comp Var minus Check HJD 2400000+ Phase Delta B DeltaV Delta(B-V) DeltaB DeltaV Delta(B-V) Obs. 45844.520 0.976 -1.530 ... ... -2.663 ... Fd 45847.425 0.982 -1.521 -0.868 -0.653 -2.634 -2.289 -0.345 Fd 45848.556 0.984 -1.459: -0.852 -0.607: -2.661 -2.300 -0.361 Fd 45853.392 0.994 -1.519 -0.852 -0.667 -2.669 -2.332 -0.337 Fd 45854.471 0.996 -1.511 -0.851 -0.660 -2.713: -2.379: -0.334: Fd 45855.409 0.998 -1.500 -0.830 -0.670 -2.666 -2.307 -0.359 Fd 45857.407 0.001 -1.537: ... ... -2.703: ... ... Fd 45862.514 0.011 -1.518 -0.865 -0.653 -2.671 -2.301 -0.370 Fd 45863.453 0.013 -1.535 -0.865 -0.670 -2.689 -2.310 -0.379 Fd 45869.507 0.025 -1.506 -0.825 -0.681 -2.652 -2.300 -0.352 Fd 45871.431 0.029 ... -0.860 ... ... 2.320 ... Se 45879.422 0.045 -1.513 -0.828 -0.685 ... ... ... Fd 45889.458 0.064 -1.571 -0.843 -0.728 ... ... ... Fd 45892.503 0.070 -1.486 -0.777 -0.709 ... ... ... Fd 45904.5 0.094 -1.466 -0.808 -0.658 ... ... ... Fd Photometric observations of Theta CrB in 1984.Observers are M.Fernandes (Fd) and B. Schlereth (Se). Comparison star Eta CrB, check star HD 138341. Phases are computed according to the ephemeris Min I = JD 2412650.1+ 510.87d E (Harmanec 1983). ":" denotes less reliable measurements. They were ignored in forming the mean values given in the text. The dispersion curve for each plate is computed as a 4th-order polynomial fitted by least squares to reference line measurements (about 20 iron arc lines, wavelengths taken from standard sources). Stellar lines measured were Hgamma to H11, and the He I lines lambda4026 and lambda3819, but only the Balmer lines were usable for radial velocity determination. All lines are quite broad and shallow so that the errors are rather large. Internal mean measurement errors range from +- 5 km/s to +- 15 km/s. A cursory look at the spectrograms does not reveal anything unusual, like emission peaks; however, such features as weak shell lines or absorption cores (noticed in some spectra) presumably have influenced the results. Systematic effects show up also in the radial velocities derived from different lines in the same spectrum, which become more negative with increasing Balmer number. Nevertheless, mean values formed from the same Table II Plate No. HJD 2400000+ Phase Hgamma Hdelta Hepsilon H8 H9 H10 H11 RV CS 7696 45 838.408 0.964 - 19.5 - 25.1 - 37.1 - 24.6 - 29.4 - 49.7 - 33.1 - 31.2 CS 7699 45 841.592 0.971 - 24.4 - 19.3 - 32.1 - 13.4 - 48.2 - 34.4 - 55.9 - 32.1 CS 7700* 45 841.599 0.971 + 7.9 - 9.1 - 4.2 - 29.2 - 14.4 - 26.0 - 25.2 (- 14.3) CS 7710 45 843.639 0.975 - 11.3 - 5.9 - 27.4 - 20.7 - 50.2 - 41.1 - 36.0 - 27.5 CS 7711 45 843.648 0.975 - 12.1 - 22.4 - 23.5 - 46.4 - 39.2 - 41.9 - 53.6 - 34.2 CS 7713* 45 848.517 0.984 - 11.1 - 46.4 - 93.2 - 19.5 - 61.1 - 97.4 -104.9 (- 61.9) CS 7715 45 863.487 0.013 + 2.5 - 37.7 - 35.8 - 49.4 + 1.7: - 52.9 - 44.0 - 30.8 CS 7716 45 863.498 0.013 - 15.4 - 22.4 - 39.3 - 42.9 - 45.0 - 25.2 - 31.7 - 31.7 CS 7726 45 866.458 0.019 - 2.8 - 21.1 - 30.7 - 33.2 - 18.6 - 52.3 - 54.1 - 30.4 CS 7728 45 869.398 0.025 - 27.9 - 6.8 - 24.9 - 48.0 - 49.0 - 18.3 - 32.1 - 29.6 CS 7745 45 870.407 0.027 - 13.5 - 6.8 - 36.6 - 28.5 - 34.5 - 54.9 - 38.0 - 30.4 CS 7763* 45 871.388 0.029 + 19.8 - 14.9 - 18.5 - 26.0 - 7.2 - 33.6 - 47.5 (- 18.3) CS 7784 45 880.500 0.047 - 6.8 - 7.7 - 32.9 - 44.2 - 47.3 - 72.7 - 79.5 - 41.6 CS 7790 45 894.400 0.074 + 0.8 - 30.2 - 28.0 - 36.1 - 15.7 - 10.2 - 22.6 - 20.3 CS 7804 45 911.389 0.107 - 28.2 - 33.3 - 36.4 - 44.4 - 42.5 - 47.4 + 3.3: - 31.7 < RV > 45 865 0.017 - 13.2 - 19.9 - 32.1 - 36.0 - 38.1 - 41.8 - 43.7 - 31.1 sigma +/- 10.5 +/- 11.0 +/- 5.2 +/- 11.9 +/- 12.2 +/- 17.4 +/- 16.0 +/- 4.8 Measurements of the radical velocity (in km/s) of Theta CrB in 1984. The spectrograms CS 7700, CS 7713 and CS 7763 were disregarded in forming the averages of Table 2. Sigma is the standard deviation of the values in the respective column. set of lines for each spectra should at least contain information about radial velocity changes. If we condense successive radial velocity measurements into group averages, we obtain RV = -31.4 +/- 1.4 km/s at Phase 0.971 -30.6 +/- 0.3 km/s at Phase 0.019 -31.5 +/- 6.2 km/s at Phase 0.076 i.e. no significant change in radial velocity, whereas the spectroscopic orbit of Harmanec (1983) predicts a rapid decrease of about 30 km/s during the time interval covered by our observations. Incidentally, let us note, that the most reliable RV determinations of Theta CrB available in the literature - those of Poeckert and Duric (1980) - are also consistent with the assumption of constant radial velocity (at about -29 km/s). We therefore conclude that the orbit given by Harmanec is not real. Acknowledgements: Thanks are due to B. Schlereth, Hassfurt, for communicating his measurements of Theta CrB. B.-C. Kamper would like to thank Prof. E.H. Geyer for hospitality at the Hoher List Observatory. M. FERNANDES B.-C. KAMPER B. NELLES * Berliner Arbeitsgemeinschaft Observatorium Hoher List fur Veranderliche Sterne e.V. (BAV) der Universitatssternwarte Bonn Munserdamm 90, D-1000 Berlin 41 D-5568 Daun/Eifel, F.R.G. *) Now at ZEISS, Abt. P-AP, Postfach 1369, D-7082 Oberkochen, F.R.G. References: Harmanec, P.: 1983, Bull. Astron. Inst. Czechoslovakia 34, 324. [BIBCODE 1983BAICz..34..324H ] Nicolet, B.: 1978, Astron. Astrophys. Suppl. 34, 1-49. [BIBCODE 1978A&AS...34....1N ] Poeckert, R., Duric, N.: 1980, Publ. Dom. Astrophys. Obs. 15, 327. [BIBCODE 1980PDAO...15..327P ] Roark, T.P.: 1971, Astron J. 76, 634. [BIBCODE 1971AJ.....76..634R ]