COMMISSIONS 27 AND 42 OF THE IAU 
           INFORMATION BULLETIN ON VARIABLE STARS 
                        Number 3713 
 
                                              Konkoly Observatory 
                                              Budapest 
                                              21 April 1992 
 
                                              HU ISSN 0374-0676 
 
 
         1990 AND 1991 UBVRI PHOTOMETRY OF FK COMAE 
 
        During 1988 and 1989, Heckert and Maloney (1992) 
performed UBV photometry of FK Comae Berenices (HD 117555), 
the prototype star of the FK Comae class of variable stars. 
We continue this work with 1990 and 1991 UBVRI photometry 
 
        We did the photometry on 10 nights between 13 and 30 
May 1990, and on 13 nights in 1991 between 7 and 9 March and 
between 12 and 26 May. We used the 0.6-m telescope at Mount 
Laguna Observatory operated by San Diego State University. 
The photometer used a different tube from that used for the 
1988 and 1989 observations. The new tube was a Hamamatsu 
GaAs tube operated at -1450V. We usually used a 19" aperture 
but used larger apertures as seeing required. Data were 
transformed to the standard Johnson-Cousins UBVRI system. HD 
117567 was the comparison star, and HD 117876 was the check. 
We find no evidence for variability in the comparison star. 
For reasons discussed by Heckert and Maloney (1992), we used 
c=2442192.345 + 2.400E (Chugainov 1976) to calculate the 
phases. 
        Flares are often observed on FK Com. Morris and 
Milone (1983) observed several flares on FK Com. Heckert and 
Maloney (1992) also observed a flare during 1989. Our 
practice of averaging nightly observations from a short time 
period into a single nightly point makes it difficult to 
distinguish flares; however, we observed another flare 
during 1991. The U-B point at phase 0.64 in our 1991 data is 
about 0.15 magnitudes brighter than the other points on that 
part of the light curve (Figure 3). This point is only about 
0.15 magnitudes too bright at B-V and V (Figures 1 & 2). At 
V-R an V-I there appears to be no significant increase in 
brightness (Figure 4). These data were taken on the night of 
21 May 1991 UT at about 09:15 UT under excellent sky 
conditions. The color behavior of this flare is similar to 
that observed in the previous flares. The flare is brightest 
at U, much less so at V, and significant at R and I. Morris 
and Milone (1983) note that all five flares reported up to 
the time of their work occured between phases 0.4 an 0.9. 
The 1989 and 1991 flares at phases 0.5 and 0.64 continue 
this trend. We have no information about the total energy or 
duration of the flare. We do however remove this point when 
considering the nonflare behavior of FK Com below. 


                    [FIGURE 1]
                    [FIGURE 2]
                    [FIGURE 3]
                    [FIGURE 4]


        We plot our V differential magnitudes in Figure 1. 
The phase of minimum light is about 0.17 in 1990 and about 
0.3 to 0.35 in 1991. These results compare to the phases of 
minimum light of about 0.6 in 1988 and about 0.15 in 1989 
(Heckert and Maloney 1992). The amplitude of variation is 
about 0.15 magnitudes for 1988, 1989, and 1990 (with small 
year to year fluctuations) and about 0.11 magnitudes in 
1991. The level of light at maximum is about the same for 
both 1988, 1989, and 1991. It is about 0.02 magnitudes 
brighter in 1990. From this information we conclude, in the 
context of the starspot model, that the major spot or spot 
group either migrated significantly in longitude or 
disappeared and reformed at a new longitude between 1988 and 
1989. The spot then migrated and insignificant amount 
between 1989 and 1990 and the migration rate increased from 
1990 to 1991. The migration is in the sense of increasing 
phase. In addition, the area covered by the major spot 
fluctuated a small amount from 1988 to 1990 and then 
decreased in 1991. From the levels of the maximum light we 
conclude that there were smaller spots spread around the 
star that disappeared or decreased in 1990. The color curves 
generally show minima and maxima at the same phases as the V 
light curves. The star is reddest at minimum light as would 
be expected if cool spots cause the brightness variations. 
        Ron Angione scheduled generous amounts telescope of 
time at Mt. Laguna for this work. We also acknowledge 
support from The Research Corporation. 

 
                                P. A. HECKERT 
                                G. V. MALONEY 
                                M. STEWART 
                                Dept. of Chem. & Physics 
                                Western Carolina University 
                                Cullowhee, NC 28273 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 
Morris, S.I.; Milone, E.F.: 1983, Pub. Astron. Soc. Pac., 95, 376  [BIBCODE 1983PASP...95..376M ]