COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 3699 Konkoly Observatory Budapest 3 March 1992 HU ISSN 0374 - 0676 PHOTOMETRIC OBSERVATIONS OF R CrB FOLLOWING THE 1983 MINIMUM R CrB is the prototype of one of the most interesting classes of variables. It is subject to abrupt declines in brightness followed by a slower recovery, often accompanied by fluctuations. Photometric UBVRI-observations during one of these minima were obtained at an altitude of 3100 m Terscol Peak (the Caucasus) with the 0.5 m reflector using an automatic single- channel photometer in 1983-1984. These data of R CrB are listed in Table 2, and are plotted against Julian Date in Fig. 1. Our magnitudes are accurate to 0.01-0.02m and the colour indices to 0.01-0.04m, except at the deep minimum phase, where the observational errors are larger because the variable was observed at low altitude and was close to the limiting magnitude for the 50-cm telescope photometry. The magnitudes and colours of the comparison stars, determined by means of comparison with Johnson's standard stars gamma and delta CrB, are given in Table 1. The observations of R CrB enable us to compare the colour curves of the present decline with other declines of R CrB. As seen from Fig. 1, in the 1983 minimum all colour curves show a redward trend after the star begins to decline in V (this reddening totals 0.25m in U-B, 0.4m in B-V, 0.5m in V-R and by 0.35m in R-I). As the brightness continues to fall toward minimum, however, the colour curves show a blueward trend, as they usually do. On the rising branch, after the variable has recovered by 2m it has became redder again. On the rising branch, the availability of the reddening is a peculiarity of the R CrB minima. The distinctive feature of the 1983 minimum was an appreciable reddening occurred at visible wavelenghts on the descending branch of the light curve when R CrB had faded by Delta m_v = 3.5m. As seen from Fig. 1, during brightness oscillations, having amplitudes larger than ordinary ones, occurred at the rising branch, both in the first part (when m had recovered to 11.5m) and near the end (m_v = 6.5m), the amplitude of the oscillation in the U-B index was significantly larger than it was when the star was fluctuating while in its normal bright state. [FIGURE 1] Table 1. Comparison stars Star V U-B B-V V-R R-I BD +28 2475 7.45m 0.03m 0.47m 0.43m 0.28m BD +28 2469 8.09 0.11 0.62 0.52 0.37 (anonymous) alpha=15h 47.7m, 12.25 0.19 0.71 0.58 0.33 delta=28d 16 Table 2. Observations of R CrB JD V U-B B-V V-R R-I 2445000+ 526.38 5.94m 0.11m 0.63m 0.53m 0.31m 527.36 5.88 0.10 0.60 0.52 0.32 528.36 5.87 0.09 0.62 0.50 0.29 529.34 5.87 0.07 0.60 0.53 0.30 530.40 5.89 0.06 0.59 0.53 0.25 532.43 5.77 0.04 0.61 0.49 0.31 533.45 5.85 0.04 0.60 0.49 0.28 540.33 5.86 0.04 0.58 0.54 0.30 544.38 5.82 0.06 0.63 0.50 0.30 545.37 5.82 0.10 0.62 0.52 0.28 547.34 5.82 0.08 0.55 0.51 0.33 555.29 5.83 0.06 0.60 0.51 - 556.34 5.80 0.08 0.59 0.50 0.30 558.33 5.81 0.04 0.58 0.50 0.31 561.34 5.89 0.06 0.60 0.49 0.32 564.35 6.00 0.06 0.60 0.50 0.30 589.35 9.43 0.25 0.90 0.76 0.45 592.33 10.04 0.26 1.00 0.88 0.48 594.32 10.11 0.30 0.97 0.89 0.48 596.33 10.61 0.18 1.01 0.90 0.54 599.32 11.27 -0.06 1.07 1.05 0.55 607.33 12.18 -0.41 0.96 0.96 0.61 Table 2 (continued ) JD JD 2445000 V U-B B-V V-R R-I 2445000 V U-B B-V V-R + + 608.32 12.26 -0.30 0.90 0.93 0.58 761.54 11.88 0.38 1.26 1.35 609.25 12.40 -0.24 0.75 0.89 0.54 790.48 9.65 0.80 1.32 1.30 514.21 13.40 -0.58 0.34 0.63 0.57 794.42 9.49 0.81 1.32 1.27 615.20 13.63 -0.65 0.23 0.46 1.08 818.51 7.70 0.60 0.99 0.49 616.38 13.47 -0.42 0.24 1.49 - 824.56 7.30 0.56 0.96 0.79 617.21 13.35 -0.62 0.53 0.68 0.40 832.51 7.15 -0.29 0.92 0.79 620.18 13.30 -0.84 0.45 0.62 0.25 842.42 7.07 -0.17 0.88 0.75 621.20 13.45 -0.91 0.76 0.25 0.39 843.43 7.06 -0.15 0.87 0.73 623.21 13.40 -0.50 1.40 0.20 0.40 859.49 6.54 0.02 0.75 0.67 624.20 13.60 -0.30 0.50 0.10 0.80 860.49 6.52 -0.01 0.74 0.65 625.21 14.19 -0.91 0.43 1.38 0.64 863.48 6.54 -0.02 0.75 0.64 632.21 13.73 -0.09 0.11 0.85 0.96 869.42 6.62 -0.05 0.78 0.66 635.21 13.63 -0.70 0.50 0.30 - 881.38 6.78 -0.03 0.79 0.67 636.21 13.77 -0.50 0.32 0.25 - 882.27 6.82 0.02 0.79 0.66 643.17 13.90 0.05 0.50 0.80 1.10 884.42 6.82 0.28 0.75 0.63 647.17 13.26 -0.30 0.57 0.84 0.57 885.37 6:81 0.30 0.75 0.64 715.60 11.18 0.72 1.45 1.28 0.61 948.29 6.64 0.42 0.81 0.67 725.58 11.35 0.67 1.34 1.29 0.60 949.29 6.63 0.43 0.80 0.66 730.58 11.46 0.66 1.25 1.24 0.54 950.24 6.61 0.38 0.82 0.65 733.58 11.51 - 1.27 1.14 0.53 956.25 6.55 0.29 0.77 0.60 735.60 11.31 0.59 1.26 1.04 0.50 959.27 6.50 0.30 0.74 0.62 736.56 11.27 0.53 1.23 1.07 0.55 960.24 6.52 0.24 0.75 0.61 745.56 11.54 0.40 1.66 1.21 0.56 961.24 6.47 0.28 0.72 0.60 746.60 11.58 0.35 1.47 1.20 0.61 965.23 6.50 0.28 0.72 0.60 747.57 11.60 0.30 1.40 1.40 0.59 966.22 6.52 0.27 0.74 0.61 752.57 11.99 0.18 1.33 1.62 - 968.23 6.49 0.29 0.75 0.60 754.49 12.03 0.30 1.29 1.55 - 969.23 6.50 0.32 0.74 0.61 758.47 12.00 0.23 1.33 1.49 - 970.22 6.49 0.34 0.76 0.62 R.I. GONCHAROVA Main Astronomical Observatory of Ukrain Academy of Sciences Kiev, Ukraine