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\IBVShead{4627}{4 September 1998}

\IBVStitle{1997 PHOTOMETRY OF CG CYGNI}
\IBVSauth{Paul A. HECKERT}
\IBVSinsto{Dept. of Chem. \& Physics, Western Carolina University, Cullowhee, NC 28723 USA}

\SIMBADobj{CG Cyg}

\begintext

CG Cygni (= \# 177 in the catalog of Strassmeier et al. 1993) is a short
period eclipsing RS CVn system. Zeilik et al. (1994) model the available
data from 1922 to 1993. They also review the literature on this system.
Dapergolas et al. (1994 and previous work) have done considerable recent B
and V photometry of this system. Heckert (1994, 1995) model 1994 and 1995
light curves of this system. This work continues with the 1997 light curves.

I observed CG Cyg on the nights of 9, 12, 13, 14, 15, and 16 August 1997
with the San Diego State University 61-cm telescope on Mt. Laguna. The
photometer and observing techniques are the same as for Heckert (1994). The
light curves, with 144 data points in each filter, are plotted in Figures 1
and 2 in the standard Johnson--Cousins system. The phases are computed using
the ephemerides of Sowell et al. (1987). The small amplitude out-of-eclipse
variations discussed by Zeilik et al. (1994) are not visible in these 1997
light curves. These variations are observed as recently as 1994 and to a
lesser extent 1995 (Dapergolas et al. 1994, Heckert 1994, 1995).

Using Budding and Zeilik's (1987) Information Limit Optimization Technique
(ILOT), I modeled the data. Briefly, the ILOT extracts a distortion wave
from the initial binary fit. This wave is then fit for two circular 0K
spots. The fits for each color are performed independently. Figures 3 and 4
show the V band fits. The latitude is the most difficult spot parameter to
fit. When unable to fit the latitude of the second spot, I fixed the value
where it seemed to be converging in trial fits. Such values have no reported
error bars in the table below. The reported longitude, latitude and radius
of each spot are in degrees. I get:

\vskip 5mm 
\centerline{Spot Fits}

\begin{center}
\begin{tabular}{lcccc}
\hline
& B band & V band & R band & I band \\ 
\hline
\\
Longitude$_{1}$ & 98.6$\pm $2.5 & 103.7$\pm $4.5 & 105.4$\pm $4.8 & 104.0$%
\pm $5.7 \\ 
Latitude$_{1}$ & 70.2$\pm $3.2 & 68.6$\pm $5.8 & 70.5$\pm $4.0 & 72.6$\pm $%
4.7 \\ 
Radius$_{1}$ & 31.8$\pm $3.0 & 28.0$\pm $4.5 & 27.8$\pm $3.4 & 27.7$\pm $4.4
\\ 
Longitude$_{2}$ & 221.5$\pm $7.4 & 213.5$\pm $15.9 & 216.9$\pm $11.8 & 211.8$%
\pm $11.4 \\ 
Latitude$_{2}$ & 0 & 0 & $-$5.9$\pm $79.4 & 20 \\ 
Radius$_{2}$ & 8.8$\pm $0.7 & 7.8$\pm $1.1 & 8.3$\pm $1.8 & 8.2$\pm $1.3 \\ 
$\chi ^{2}$ & 233.8 & 179.9 & 175.0 & 131.0 \\ \hline
\end{tabular}
\end{center}

\IBVSfig{6cm}{4627-f1.ps}{}
\IBVSfig{6cm}{4627-f2.ps}{}
\IBVSfig{6cm}{4627-f3.ps}{}
\IBVSfig{6cm}{4627-f4.ps}{}

During 1997 there was a spot in each Active Longitude Belt. The spot in the
90\deg\  ALB was a fairly large high latitude spot. The 270\deg\ 
ALB contained a smaller low latitude spot. Both of these spots are new
rather than one of the spots found in the 1995 or 1994 light curves (Heckert
1994,1995). A small low latitude spot is in the 270\deg\  ALB, which
had a large high latitude spot in 1995. Spots on the sun tend to disperse
and reform at different latitudes rather than migrate in latitude. Hence,
this spot is likely a new spot rather than a spot that changed size and
migrated. The 90\deg\  ALB had a large high latitude spot in 1997 but
no spot in 1995.

After performing the spot fits, I performed clean fits to the light curves
with the effects of the distortion wave removed. I get:

\vskip .5cm 

\centerline{Clean Fits}
\begin{center}
\begin{tabular}{lcccc}
\hline
& B band & V band & R band & I band \\ 
\hline
\\
L$_{1}$ & 0.747$\pm $0.010 & 0.716$\pm $0.013 & 0.718$\pm $0.012 & 0.724$\pm 
$0.059 \\ 
k(=r$_{2}$/r$_{1}$) & 0.831$\pm $0.018 & 0.837$\pm $0.022 & 0.805$\pm $0.021
& 0.767$\pm $0.115 \\ 
$\Delta \theta _{0}$ & $-$2.997$\pm $0.114 & $-$2.968$\pm $0.122 & $-$2.884$\pm $%
0.126 & $-$2.840$\pm $0.129 \\ 
r$_{1}$ & 0.256$\pm $0.005 & 0.255$\pm $0.005 & 0.259$\pm $0.005 & 0.261$\pm 
$0.016 \\ 
i(deg) & 83.3 & 82.8 & 82.8 & 83.1$\pm $1.6 \\ 
L$_{2}$ & 0.236$\pm $0.011 & 0.266$\pm $0.014 & 0.270$\pm $0.013 & 0.269$\pm 
$0.061 \\ 
q(=m$_{2}$/m$_{1}$) & 0.393$\pm $0.056 & 0.411$\pm $0.078 & 0.386$\pm $0.090
& 0.353$\pm $0.206 \\ 
$\chi ^{2}$ & 132.3 & 90.1 & 88.7 & 66.0 \\ \hline
\end{tabular}
\end{center}
\vskip .5cm

As defined by Budding and Zeilik (1987), L$_{1}$ and L$_{2}$ are the
fractional luminosities of the primary and secondary star. They are
normalized to sum to approximately but not exactly one. The inclination, i,
is in degrees. k and q are the ratios of the radii and masses. The radius of
the primary, r$_{1}$, is in units of the orbital separation. $\Delta \theta
_{0}$ is the difference between the observed and computed times when the
eclipses occur expressed in degrees. Averaging the values of $\Delta \theta
_{0}$ for the different filters, and converting into days I find that the
eclipses occurred 0.0051$\pm $0.0001 days after they are predicted to occur
during this epoch. This difference is very similar to that observed in 1995
but differs from 1994 (Heckert 1994, 1995).

The mass ratio, q, is much lower than for previous work. Popper (1993, 1994)
get 0.84 and 0.86, Jassur (1980) gets 0.95, Heckert (1994, 1995) get 0.53
and 0.81. Most other previous workers get 1.0 (Budding and Zeilik 1987,
Zeilik et al. 1994, Naftilan and Milone 1985, and Sowell et al. 1987). The
average value for the four 1997 light curves is 0.39. Mass ratios found by
analysis of light curves are less reliable than those found from spectral
data. However the fact that the 1997 as well as the 1994 and 1995 light
curves all yield low values for the mass ratio suggests that the previously
reported values lower than 1.0 are more likely to be correct than the more
commonly reported values of 1.0.

I thank Ron Angione for scheduling generous amounts of observing time at Mt.
Laguna. I also acknowledge support from a Cottrell College Science Award of
The Research Corporation for this work.


\references

Budding, E. and Zeilik, M., 1987, {\it Astrophys. J.}, {\it 319}, 827

Dapergolas, A., Kontizas, E., and Kontizas, M., 1994, {\it Inf. Bull. on
Var. Stars.}, No.\,4051

Heckert, P.A., 1994, {\it Inf. Bull. on Var. Stars.}, No.\,4127

Heckert, P.A., 1995, {\it Inf. Bull. on Var. Stars.}, No.\,4371

Jassur, D.M.Z., 1980, {\it Ap. Space Sci.}, {\bf 67}, 19

Naftilan, S.A., Milone, E.F., 1985, {\it AJ}, {\bf 90}, 761

Popper, D.M., 1993, {\it Astrophys. J.}, {\bf 404}, L67

Popper, D.M., 1994, {\it Astron. J.}, {\bf 108}, 1091

Sowell, J.R., Wilson, J.W., Hall, D.S., and Peyman, P.E., 1987, {\it Pub.
Astron. Soc. Pac.}, {\bf  99}, 407

Strassmeier, K., et al., 1993, {\it Astron. \& Astrophys. Suppl.}, {\bf 100}, 173

Zeilik, M., Gordon, S., Jaderlund, E., Ledlow, M., Summers, D.L., Heckert,
P.A., Budding, E., and Banks, T.S., 1994, {\it Astrophys. J.}, {\bf 421}, 303

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