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\IBVShead{5419}{26 May 2003}

\IBVStitle{2001 and 2003 Photometry of WY Cancri}
\IBVSauth{HECKERT, PAUL A.}

\IBVSinsto{Dept. of Chem. \& Physics, Western Carolina University, Cullowhee, NC 28723 USA}

\SIMBADobj{WY Cnc}

\begintext

\vspace*{-0.9cm}

As part of an ongoing study of WY Cancri, (\#82 in the catalog of
Strassmeier et al. 1993) a short period eclipsing RS CVn system, I collected
new optical photometry in 2001 and 2003. Heckert (2001) and Heckert et al.
(1998) have collected annual light curves of WY Cnc since 1988. These works
note secular luminosity increases of nearly 0.1 magnitudes in both 1988 and
1997, which may signal the onset of a new cycle in spot activity with a
change in the direction of longitudinal spot migration. Kjurkchieva et al.
(2003) report photometry and spectroscopy during 2001. They note a secular
luminosity increase in February 2001, after my 2001 data were taken. Their
spectroscopy also confirms recent detections (Pojmanski, 1998; Ar\'{e}valo
and L\'{a}zaro, 1999) of spectral lines from the secondary in this system,
which has previously been classified as a single lined system.

I observed WY Cnc with the San Diego State University 61-cm telescope on 
Mt.~Laguna. The 2001 light curves were obtained on the nights of December 30,
2000 and January 2, 3, \& 6, 2001. The 2003 light curves were obtained on
January 9, 10, 11, 13, 18, 21,\& 24, 2003. I used SAO 80583 as the
comparison star. The light curves, with 135 data points per filter in 2001
and 132 in 2003, are plotted in Figures 1 and 2. The data are differential
magnitudes (var-comp) in the standard Johnson-Cousins system. I used the
ephemeris of Hall and Kreiner (1980):

$\phi _{0}$=2426352.3895+0.82937122 E.

I modelled the data using Budding and Zeilik's (1987) Information Limit
Optimization Technique (ILOT). Initial values for stellar parameters were
the same as those of Heckert et al. (1998) and Heckert (2001). I adopted
temperatures of 5520K and 3500K for the primary and secondary stars. After
the initial fit, the ILOT extracts a distortion wave which I then fit for
two circular 0K spots. The fits for each color are performed independently.
The reported longitude, latitude and radius of each spot are in degrees, and are given in Table~1.

\begin{table}[!ht]
\small
\centerline{{\bf Table 1.} Spot Fits}
\begin{center}
\begin{tabular}{lcccc}
\hline
2001 & B band & V band & R band & I band \\ \hline
Longitude$_{1}$ & 287.5$\pm $1.7 & 286.6$\pm $2.5 & 286.4$\pm $2.8 & 284.8$%
\pm $4.0 \\ 
Latitude$_{1}$ & 59.8$\pm $3.8 & 57.8$\pm $8.0 & 60.0$\pm $9.5 & 60.3$\pm $%
17.5 \\ 
Radius$_{1}$ & 26.1$\pm $2.4 & 22.3$\pm $3.8 & 21.5$\pm $4.5 & 19.7$\pm $7.3
\\ 
Longitude$_{2}$ & 146.0$\pm $4.6 & 148.3$\pm $6.3 & 149.5$\pm $9.3 & 149.4$%
\pm $12.0 \\ 
Latitude$_{2}$ & 0.0$\pm $14.5 & 0.0$\pm $23.8 & 0.0$\pm $19.7 & 0.0$\pm $%
20.1 \\ 
Radius$_{2}$ & 9.3$\pm $0.5 & 8.7$\pm $0.6 & 8.3$\pm $0.7 & 8.1$\pm $0.8 \\ 
$\chi ^{2}$ & 68.4 & 52.6 & 44.9 & 44.0 \\ \hline
2003 &  &  &  &  \\ 
Longitude$_{1}$ & 93.2$\pm $4.1 & 87.5$\pm $4.7 & 90.2$\pm $6.6 & 91.3$\pm $%
7.9 \\ 
Latitude$_{1}$ & 74.4$\pm $4.4 & 73.5$\pm $5.8 & 76.0$\pm $6.6 & 78.0$\pm $%
6.7 \\ 
Radius$_{1}$ & 25.5$\pm $4.7 & 22.6$\pm $5.4 & 21.5$\pm $6.6 & 21.2$\pm $7.4
\\ 
Longitude$_{2}$ & 299.7$\pm $4.6 & 302.0$\pm $6.8 & 303.7$\pm $9.1 & 305.4$%
\pm $10.5 \\ 
Latitude$_{2}$ & 0.0$\pm $19.6 & 0.0$\pm $20.8 & 0.0$\pm $27.0 & 0.0$\pm $%
29.4 \\ 
Radius$_{2}$ & 9.1$\pm $0.7 & 8.5$\pm $0.8 & 7.8$\pm $0.9 & 7.0$\pm $1.0 \\ 
$\chi ^{2}$ & 161.4 & 110.5 & 91.4 & 70.3 \\ \hline
\end{tabular}
\end{center}
\vspace*{-0.8cm}
\end{table}


Being more difficult to fit, the latitudes are less reliable than the other
parameters. However the two spots during both years include both high and
low latitudes. Heckert et al. (1998) note a tendency for spots in the 270\deg\ 
 ALB to be at higher latitudes than those in the 90\deg\ ALB. This
tendency appears to hold in the 2001 data. The 2003 data however show the
reverse tendency. The 90\deg\ ALB spot is at higher latitude. By comparing
the R or I data to the 0K spot solutions at B or V, the ILOT can estimate
spot temperatures. Doing so I find an average value of the spot temperature
of T$_{s}$=3993K$\pm $321K for 2001 and T$_{s}$=3930K$\pm $100K for 2003.

Kjurkchieva et al. (2003) modelled the spots in their light curves from
November and December 2000. With spots at 220\deg\ and 345\deg\ longitude,
their models differ from this work. To check my models for nonunique
solutions, I tried using their spot solution as an initial guess for
modeling my data. The solution converged to that reported here. Hence the
spots changed rapidly. Noting that Kjurkchieva et al. (2003) observed a
secular luminosity increase in February 2001, suggests that rapid changes in
the spot structure occur just before the secular luminosity increases. If
these luminosity increases result in some way from increased magnetic
activity, such rapid changes would be expected. This magnetic activity could
be either spot activity that disappears or a bright magnetic network similar
to, but much more extensive than, that on the Sun.  Figure 3 plots the
estimated unspotted light level following Heckert (2001). The data from this
work and Kjurkchieva et al. (2003) are added to Heckert's (2001) original
figure. In addition to the original caveats, note that the Kjurkchieva et
al. (2003) data are in the instrumental system. Hence the apparent brightness
decrease from December 2000 to January 2001 is likely a calibration
artifact. If so, the February 2001 secular luminosity increase is closer in
brightness to those of 1997 and 1988 than it appears in the figure. Also
note that the February 2001 data are very limited phase coverage. The
secular luminosity increase seems to rise on a time scale of a few months.

\vspace*{-0.05cm}

After the spot fits, I performed clean fits to the light curves removing the
effects of the distortion wave from the spot as modelled in that filter. The
fits at each wavelength were done independently. The color independent
parameters generally agree to within the quoted errors. Table~2
shows values for each filter and the mean for the wavelength independent
parameters. Figure 4 shows the $V$ band clean fits.

\vspace*{-0.05cm}

\begin{table}[!ht]
\small
\centerline{{\bf Table 2.} Clean Fits}
\begin{center}
\begin{tabular}{lccccc}
\hline
2001 & B band & V band & R band & I band & Mean \\ \hline
L$_{1}$ & 0.961$\pm $0.004 & 0.956$\pm $0.005 & 0.940$\pm $0.005 & 0.912$\pm 
$0.005 &  \\ 
k(=r$_{2}$/r$_{1}$) & 0.612$\pm $0.003 & 0.611$\pm $0.004 & 0.612$\pm $0.004
& 0.607$\pm $0.005 & 0.611 \\ 
$\Delta \theta _{0}$ & 10.597$\pm $0.115 & 10.589$\pm $0.122 & 10.542$\pm $%
0.127 & 10.485$\pm $0.133 & 10.553 \\ 
r$_{1}$ & 0.241$\pm $0.003 & 0.240$\pm $0.003 & 0.236$\pm $0.003 & 0.237$\pm 
$0.003 & 0.239 \\ 
i(deg) & 90.0$\pm $1.3 & 90.0$\pm $1.2 & 90.0$\pm $1.4 & 90.0$\pm $1.4 & 90.0
\\ 
L$_{2}$ & 0.028$\pm $0.005 & 0.034$\pm $0.005 & 0.050$\pm $0.006 & 0.075$\pm 
$0.006 &  \\ 
q(=m$_{2}$/m$_{1}$) & 0.326$\pm $0.054 & 0.326$\pm $0.070 & 0.335$\pm $0.094
& 0.313$\pm $0.124 & 0.325 \\ 
$\chi ^{2}$ & 41.9 & 32.0 & 30.2 & 32.6 &  \\ \hline
2003 &  &  &  &  &  \\ 
L$_{1}$ & 0.995$\pm $0.004 & 0.972$\pm $0.004 & 0.951$\pm $0.004 & 0.924$\pm 
$0.004 &  \\ 
k(=r$_{2}$/r$_{1}$) & 0.638$\pm $0.012 & 0.626$\pm $0.007 & 0.627$\pm $0.006
& 0.617$\pm $0.006 & 0.627 \\ 
$\Delta \theta _{0}$ & 11.916$\pm $0.105 & 11.953$\pm $0.109 & 11.910$\pm $%
0.113 & 11.871$\pm $0.117 & 11.913 \\ 
r$_{1}$ & 0.240$\pm $0.003 & 0.239$\pm $0.003 & 0.238$\pm $0.003 & 0.239$\pm 
$0.003 & 0.239 \\ 
i(deg) & 86.8$\pm $1.0 & 88.2$\pm $1.5 & 88.1$\pm $1.3 & 88.2$\pm $1.4 & 87.8
\\ 
L$_{2}$ & 0.009$\pm $0.005 & 0.025$\pm $0.005 & 0.042$\pm $0.006 & 0.070$\pm 
$0.006 &  \\ 
q(=m$_{2}$/m$_{1}$) & 0.534$\pm $0.052 & 0.550$\pm $0.067 & 0.594$\pm $0.084
& 0.593$\pm $0.100 & 0.568 \\ 
$\chi ^{2}$ & 140.4 & 95.7 & 83.6 & 66.2 &  \\ \hline
\end{tabular}
\end{center}
\vspace*{-0.6cm}
\end{table}


The quantities in Table~2 are as defined by Budding and Zeilik (1987). The fractional
luminosities of the primary and secondary components, L$_{1}$ and L$_{2}$,
are normalized to sum to approximately but not exactly 1. The sum can
deviate from unity because the normalization is performed before the light
curve is corrected for the spot effects, and subtracting the spot causes the
out of eclipse intensity to be slightly more or less than 1. These results
agree to within the errors with previous work. The mass ratio, q, has been a
particular problem for WY Cnc. The results above compare with previous
photometric values of q=0.31$\pm $0.23 and q=0.384$\pm $0.099 (Heckert, 2001
and Heckert et al., 1998). More recently it has been possible to determine
this value from spectroscopy. The photometric mass ratios and inclinations
for 2003 are very close to the spectroscopic values of q=0.59$\pm $0.07, 
i=87\deg\ and q=0.55$\pm $0.06, i=88\deg\ (Ar\'{e}valo and L\'{a}zaro, 1999 and
Kjurkchieva et al., 2003). The 2001 values however are closer to the previous
lower photometric determinations of q and the corresponding inclinations of
90\deg\ for most of the data sets. 

I thank Paul Etzel for scheduling generous amounts of observing time at Mt.
Laguna. I also acknowledge support from the Gaposchkin Research Fund of the
American Astronomical Society Small Research Grant Program.

\vspace*{-0.3cm}

\references

\strut 

Ar\'{e}valo, M. and L\'{a}zaro, C., 1999, {\it Astron. J.}, {\bf 118}, 1015

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

Hall, D.S. and Kreiner, J.M., 1980, {\it Acta Astron.}, {\bf 30}, 387

Heckert, P. A., et al., 1998, {\it Astron. J.}, {\bf 115}, 1145

Heckert, P. A., et al., 2001, {\it Astron. J.}, {\bf 121}, 1076

Kjurkchieva, D. P., et al. 2003, {\it Astron. \& Astrophys. }in press.

Pojmanski, G., 1998, {\it Acta Astron.}, {\bf 48}, 711

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

\endreferences


\IBVSfig{7cm}{5419-f1.eps}{The light curve of WY~Cnc in 2001, with 135 data points per filter.\vspace*{-1.1cm}}
%%\IBVSfigKey{5419-f1.eps}{WY Cnc}{light curve}

\IBVSfig{7cm}{5419-f2.eps}{The light curve of WY~Cnc in 2003, with 132 data points per filter.\vspace*{-1.1cm}}
%%\IBVSfigKey{5419-f2.eps}{WY Cnc}{light curve}

\IBVSfig{7cm}{5419-f3.eps}{\vspace*{-1cm}}
%%\IBVSfigKey{5419-f3.eps}{WY Cnc}{light curve}

\IBVSfig{7cm}{5419-f4.eps}{}
%%\IBVSfigKey{5419-f4.eps}{WY Cnc}{light curve}

\IBVSecomment{Figure captions corrected June 23 2004}

\end{document}

