COMMISSIONS 27 AND 42 OF THE IAU 
              INFORMATION BULLETIN ON VARIABLE STARS 
                           Number 3717 
 
                                         Konkoly Observatory 
                                         Budapest 
                                         29 April 1992 
 
                                         HU ISSN 0374 - 0676 
 
 
 
 
 
       1990 AND 1991 UBVRI PHOTOMETRY OF HD 199178 = V1794 Cyg 
 
 
 HD 199178, an FK Comae star of spectral class G5 III-IV, has been 
previously studied by Bopp et al. (1983) and Houvelin et al. (1987). 
We performed new photometry on 6 nights between 16 May and 26 May 1990 
and on 11 nights between 12 May and 26 May 1991. 
 
 We used the 24 inch telescope at Mount Laguna Observatory, which is 
operated by San Diego State University. The photometer has a 
Hamamatsu GaAs phototube, operating at -1450 volts, and a standard 
UBVRI filters. SAO 50313 was our comparison star, and SAO 50326 was 
our check. We find no evidence for variability in our comparison. 
 
 To compute the phase we use: 
 
            C=2444395.7 + 3.337d x E (Bopp et al. 1983). 
 
Our V light curves (Figure 1) show that the phase of minimum light 
migrated from about 0.5 to about 0.8 from 1990 to 1991. The two 
minima are roughly the same magnitude; however during 1991 the star is 
brighter at maximum light. The amplitude of variability decreases 
from about 0.06 mag to about 0.04 mag between 1990 and 1991. Hence, 
we conclude that the major starspot or spot group both migrated in 
longitude and shrank between 1990 and 1991. 
 
 The color curves are in Figures 2-4. The B-V, V-R and V-I curves 
generally show minima at minimum light as one would expect if the 
light variations are caused by cooler dark spots. However, the color 
variations are small making this interpretation difficult. The U-B 
curves are quite curious. The 1991 U-B curve is about 0.08 mngnitudes 
brighter than the 1990 curve. It is initially tempting to assume that 
this color difference is caused by a significant increase in the 
stellar temperature between 1990 and 1991. The shrinking of the major 
spot group between 1990 and 1991 would tend to cause the average 
temperature to increase, but the spot does not appear to have shrunk 
enough to cause the observed difference in the U-B colors. 


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

 
 What about the colors?  For a G5 III star a change of 0.08 magnitudes 
in U-B would correspond to a change of about 0.04 magnitude in B-V, if 
the color change were entirely caused by a temperature change 
(Novotny, 1973). Close examination of the B-V color curve shows that 
the 1991 data are on the average roughly 0.01 to 0.02 magnitudes 
brighter than the 1990 data. Therefore a temperature change can only 
partially explain the brightness increase in the U-B color. We do 
however note that Bopp et al. (1983) observe ultraviolet emission 
lines in HD 199178; perhaps the effects of changes in the strength of 
this emission between 1990 and 1991 contribute to the color change. 
 
 Ron Angione scheduled generous amounts of time on the Mt. Laguna 24" 
telescope for this work. The Research Corporation provided generous 
support for this work. 
 
 
                           P. A. HECKERT 
                           M. C. STEWART 
                           Dept. of Chem. & Physics 
                           Western Carolina University 
                           Cullowhee, NC 28723 USA 
 
 
References: 
 
Bopp, B.W., Africano, J.L, Stencel, R.E., Noah, P.V., Klimke, A.: 
  1983, Astrophys. J. 275, 691  [BIBCODE 1983ApJ...275..691B ]
 
Huovelin, J., Piirola, V., Vilhu, O., Efimov, Y.S. and Shakhovskoy, 
  N.M.: 1987, Astron. Astrophys. 176, 83  [BIBCODE 1987A&A...176...83H ]
 
Novotny, E.: 1973, Introduction to Stellar Atmospheres and Interiors, 
  Oxford University Press, 11  [BIBCODE 1973itsa.book.....N ]