COMMISSIONS 27 AND 42 OF THE IAU INFORMATION BULLETIN ON VARIABLE STARS Number 3954 Konkoly Observatory Budapest 22 November 1993 HU ISSN 0374 - 0676 1992 UBVRI PHOTOMETRY OF FK COMAE Heckert and Maloney (1992) and Heckert Maloney and Stewart (1992) present photometry from 1988 to 1991 of FK Comae Berenices (HD 117555), the prototype star of the FK Comae class of variable stars. In this paper, I continue this work with 1992 photometry. I performed new photometry on seven nights between 12 and 27 May 1992 and on 25 July and 4 August 1992. I used the 24 inch telescope at Mount Laguna Observatory operated by San Diego State University. During May the photometer was equipped with a Hamamatsu GaAs phototube operating at -1450V. During July and August this tube was replaced with an EMI 9789 tube operating at -1200V. The Hamamatsu tube was equipped with UBVRI filters, but the less red sensitive EMI tube was equipped with UBV filters only. The data are transformed to the standard Johnson-Cousins UBVRI system. HD 117567 was the comparison star, and HD 117876 was the check. The check star data show neither systematic differences between the transformed data taken with the different tubes nor evidence for variability in the comparison star. For reasons discussed by Heckert and Maloney (1992), we used the 2.400d period of Chugainov (1976) to calculate the phases. TABLE 1 --------------------------------------------------------------- Julian Day Phase DeltaU DeltaB DeltaV DeltaR DeltaI --------------------------------------------------------------- 2448754.851 0.378 1.434 0.985 0.522 0.285 0.078 2448755.839 0.789 1.451 0.974 0.522 0.289 0.075 2448757.844 0.625 1.461 0.986 0.527 0.297 0.081 2448759.829 0.452 1.425 0.964 0.518 0.282 0.077 2448760.841 0.873 1.449 0.977 0.521 0.287 0.078 24d8762.804 0.691 1.482 0.994 0.536 0.297 0.091 2448769.781 0.598 1.472 0.999 0.542 0.301 0.095 2448828.687 0.143 1.333 0.892 0.476 2448838.696 0.313 1.380 0.927 0.492 --------------------------------------------------------------- The differential magnitudes are in Table 1, and the B and V light curves are in Figure 1. Minimum light is at about phase 0.65. This phase of minimum light compares to 0.6, 0.15, 0.17, and 0.3 in 1988, 1989, 1990, and 1991 (Heckert and Maloney 1992, Heckert, Maloney, and Stewart 1992). In terms of the starspot model, the major spot group migrates in the sense [FIGURE 1] Figure 1. FK Comae - 1992 of increasing phase considerably in longitude on time scales of less than one year, but the migration rate seems to vary from year to year. The amplitude of variation in V is about 0.15 magnitudes for 1988, 1989, and 1990 (with small year to year fluctuations), about 0.11 magnitudes in 1991, and about 0.07 magnitudes in 1992. The level of light in V at maximum is about the same for both 1992 and 1990, which is about 0.02 magnitudes brighter than in 1988. 1989, and 1991. I conclude that the major spot group became smaller in 1991 and continued to shrink during 1992. From the levels of maximum light I conclude that there are often smaller spots spread around the star that disappeared or decreased in both 1990 and 1992. Ron Angione scheduled generous amounts telescope of time on the Mt. Laguna 24" telescope for this work. I also acknowledge generous support from The Research Corporation. P.A. HECKERT Dept. of Chem. & Physics Western Carolina University Cullowhee, NC 28723 USA References: Chugainov, P.V.; 1976; Izv. Krimskoi Astrof. Obs., 54, 89. [BIBCODE 1976IzKry..54...89C ] Heckert, P.A. and Maloney. G.V.; 1992 Inf. Bull. Var. Stars, No. 3700. Heckert, P.A., Maloney, G.V., and Stewart, M.; 1992 Inf. Bull. Var. Stars, No. 3713.