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\begin{document}

\IBVShead{5845}{29 July 2008}

\IBVStitletl{V965 Cygni, an A and F Type Very High Fill-out Binary}{ with Strong Magnetic Activity?}

\IBVSauth{SAMEC, RONALD G.$^{1,4}$; BRANNING, JEREMY$^1$; JONES, STEPHANIE M.$^1$; FAULKNER, DANNY R.$^{2,4}$; HAWKINS, NATHAN C.$^{3,4}$}

\IBVSinst{Astronomy program, Department of Physics, Bob Jones University, Greenville, SC 29614}
\IBVSinst{University of South Carolina, Lancaster}
\IBVSinst{University of Oklahoma}
\IBVSinst{Visiting Astronomer, Lowell Observatory, Flagstaff, AZ}

\SIMBADobj{V965 Cyg}

\begintext

	V965 Cygni [$\alpha$(2000)=19\hr 44\mm 09\fsec3, $\delta$(2000)=+31\deg 42\arcm 37\arcs] was observed as a part of our continuing 
study of  neglected interacting eclipsing binaries. It was discovered by Wachmann (1964) and identified as a W UMa star with 
a period of 0.64 days or possibly as an RR Lyrae type c with $\sim 1$~magnitude amplitude. He reported 7 times of minimum 
light. We recalculated his early ephemeris using our computer program using his original minima:
\begin{equation}               
{\rm HJD\ Tmin\ I} = 2435047.295\ (\pm 0.017)  + 0.640575\ (\pm 0.000009)\ {\rm d\times E}.
\end{equation}
In addition, four other times of minimum light have been published by Zejda, (2004), Hubscher, Paschke, 
Walter (2007) and by Hubscher, Paschke and Walter (2006). There have been no further references.

\IBVSfig{9cm}{5845-f1.eps}{Finding Chart, V965 Cyg Variable (V), Comparison (C) and Check (K), V' is V963 Cyg.}
\IBVSfigKey{5845-f1.eps}{V965 Cyg}{finding chart}

\vspace*{-0.4cm}

         Our $U,B,V,R,I$ light curves were taken with the Lowell 31 inch reflector in Flagstaff  with the 
LN cooled CCD camera with a metachrome coated TEK $512\times 512$ chip and standard $BVR_cI_c$ filters on 
July 19-25, 2004. Our individual observations include  83~in~$U$, 94 in $B$, 112 in $V$, 77 in $R$ and 
92 in $I$. A finding chart of V965 Cyg (V), the comparison star (C) (GSC 2656 3363) [$\alpha$(2000) = 19\hr 44\mm 
03\fsec64, $\delta$(2000) = 31\deg 41\arcm 13\farcs25], and the check star, (K) (GSC 2656 2055)  [$\alpha$(2000) = 19\hr 44\mm 
16\fsec91, $\delta$(2000) =31\deg 41\arcm 31\farcs64] are given in Figure 1. Our observations, Variable (V) minus Comparison (C) 
delta magnitudes are given in Table 1. 

\IBVSedata{5845-t1.txt}
\IBVSdataKey{5845-t1.txt}{V965 Cyg}{}

\IBVSfig{9cm}{5845-f2.eps}{Quadratic fit overlying linear residuals from Equation 4.}
\IBVSfigKey{5845-f2.eps}{V965 Cyg}{}

\vspace*{-0.4cm}

         Standard magnitudes were determined from two nights of observations, July 20 and 24. V965 Cyg is found to 
have an apparent $V$ magnitude range of $\sim 14.0-14.5$. Using a standard reddening line and a plot of $U-B$ vs. $B-V$ with a 
calibrated $U-B$ vs. $B-V$ main sequence plot (Cox, 2000) we determined a dereddened $(B-V)_0 \sim 0.07\pm 0.02$. This is that of an A3-type main 
sequence star. From this we estimate the primary component to have a temperature of about 8725~K (Cox, 2000). The check 
and comp star are both of 11th magnitude and are of K4-K5V type. The standard magnitudes and color indices with uncertainties
are given in Table~2. 

\IBVSedata{5845-t2.txt}
\IBVSdataKey{5845-t2.txt}{V965 Cyg}{}

	We determined two times of minimum light from our present observations, $${\rm HJD\ I}  = 2453211.9135 \pm 0.0005
{\rm\ and\ HJD\ II} = 2453207.7440 \pm 0.0036.$$The following ephemeris was calculated from all the available times of minimum 
light
\begin{equation}
{\rm HJD\ Tmin\ I} = 2453211.9129\ (\pm 0.0009) + 0.64056889\ (\pm 0.00000010)\ {\rm d\times E}
\end{equation}
A quadratic behavior is suggested by our timings. Our calculation gives:
\begin{equation}               
\begin{array}{cccc}    
{\rm HJD\ Tmin\ I} &= 2453211.91285 &+ 0.64056706\ {\rm d\times E} &-0.000000000065\ {\rm d\times E^2}\\
                   &\pm 0.00077 &\pm 0.00000053  &\pm  0.000000000019  \\
\end{array}    
\end{equation}               
Since we only have twelve times of minimum light (one outlier removed), and there are only six precision points (weighted 
10 times that of the earlier points), we believe the quadratic ephemeris is still tentative. However, the early points do 
supply a useful contribution to this determination. In fact the latest points,  covering only a brief period suggest only 
a linear fit. Continued monitoring of this system will result in a true picture of its period behavior. All times of minimum light are shown in Table~3 along with 
the linear and the quadratic residuals. Figure~2 shows the quadratic residuals.
	
\IBVSedata{5845-t3.txt}
\IBVSdataKey{5845-t3.txt}{V965 Cyg}{}

         A $BVRI$ synthetic light curve solution was undertaken. We first used Binary Maker~3.0 (Bradstreet, 2002) to 
explore the character of our light curves and determine initial fits to each of our $BVRI$ light curves. Using the 
average starting values from these fits, we proceeded to compute a simultaneous five color light curve solution with 
the 2004 version of the Wilson Code (Wilson and Devinney, 1971; Wilson, 1990, 1994; Van Hamme and Wilson, 1998), 
which includes Kurucz atmospheres, rather than black body, and a detailed reflection treatment along with 2-D limb 
darkening coefficients. We explored a range of mass ratios to find the best fit.
\vspace*{-0.7cm}

\IBVSfig{7cm}{5845-f3.eps}{The q vs. sum of square residual plot of Mass Ratio Search for V965 Cyg.}
\IBVSfigKey{5845-f3.eps}{V965 Cyg}{}

\vspace*{-0.9cm}

         Our first solution gave a contact binary with various characteristics which we will give below. The
mass ratio was 0.55. Since the eclipses were partial (inclination 73 degrees), we conducted a q-search in parameter
space to try to find the a better mass ratio. Our q-search is given in Figure 3. This curve is fairly shallow so the mass ratio
is still not well determined. The lowest residual mass ratio was near 0.65. Taking this solution as a starting 
point, we determined a new solution allowing q to vary. The solution was essentially the same as that resulting
from the q-search.

Our best solution and photometry reveals V965 Cyg as a hot, high fill-out contact binary (79\%) (all our solutions gave high 
fill-outs) with a large polar spot region on the secondary (less massive) component. The spot would indicate V965 Cyg has strong 
magnetic activity. The high fill-out as well as its high rotation velocity would increase the convective activity. Also, with its high
fill-out we would suspect that V965 Cyg will soon become unstable and coalesce into a FK Comae-type star. A decreasing period 
would help verify this scenario.  Radial velocity curves are needed to give a solid determination of the mass ratio. The complete Wilson code 
solution is given in Table~4. The solution overlaying the $UBVRI$ light curves are given in Figure~4,~5~and~6. Figure~7 shows the surface potential. 

\IBVSfig{7.6cm}{5845-f4.eps}{$UBVRI$ light curves and $U-B$ color curve overlaid on the Synthetic Light Curve Model.}
\IBVSfigKey{5845-f4.eps}{V965 Cyg}{light curve}

\vspace*{-1cm}

\IBVSfig{7.6cm}{5845-f5.eps}{$UBVRI$ light curves and $B-V$ color curves overlaid on the Synthetic Light Curve Model.}
\IBVSfigKey{5845-f5.eps}{V965 Cyg}{light curve}

\newpage

\IBVSfig{7.6cm}{5845-f6.eps}{$UBVRI$ light curves and $R-I$ color curves overlaid on the Synthetic Light Curve Model.}
\IBVSfigKey{5845-f6.eps}{V965 Cyg}{light curve}

\IBVSfig{6cm}{5845-f7.eps}{Stellar surface of V965 Cyg.}
\IBVSfigKey{5845-f7.eps}{V965 Cyg}{}

\newpage

\begin{table}[!hr]
\centerline{{\bf Table 4}: Synthetic curve Parameters for V965 Cyg}
\begin{center}
\begin{tabular}{ll}
\hline
Parameter                              & Best Fit Simultaneous solution\\
\hline
 $\lambda_U,\lambda_B,\lambda_V,\lambda_R,\lambda_I$ (nm)& 360, 440, 550, 640, 790 \\
$x_{bol1,2},y_{bol1,2}$                   & 0.654, 0.654, 0.119, 0.119 \\
$x_{1I,2I},y_{1I,2I}$                     & 0.446, 0.446, 0.209, 0.209 \\
$x_{1R,2V},y_{1V,2V}$                     & 0.559, 0.559, 0.251, 0.251 \\
$x_{1V,2B},y_{1B,2B}$                     & 0.660, 0.660, 0.281, 0.281  \\
$x_{1B,2U},y_{1U,2U}$                     & 0.768, 0.768, 0.311, 0.311     \\
$g_1,g_2$  				  & 1.00, 1.00  \\
$A_1,A_2$                                 & 1.0, 1.0 \\
inclination(\deg)                         & 71.5$\pm$1.5 \\
$T_1,T_2$ (K)   			  & 8725$\pm$300*, 7800$\pm$290**  \\
$\Omega_1,\Omega_2$                       & 2.867$\pm$0.022 \\
q($m_2/m_1$)  			          & 0.65$\pm$0.05     \\
fill-out                                  & 76\% \\
JD Zero					  & 2453211.9149$\pm$0.0007  \\
Period					  & 0.64100$\pm$0.00015                                                              \\
$L_1/(L_1+L_2)_I$                         & 0.64$\pm$0.05 \\
$L_1/(L_1+L_2)_R$                         & 0.65$\pm$0.06 \\
$L_1/(L_1+L_2)_V$                         & 0.67$\pm$0.06 \\
$L_1/(L_1+L_2)_B$                         & 0.69$\pm$0.07 \\
$L_1/(L_1+L_2)_U$                         & 0.69$\pm$0.07 \\
$r_1, r_2$ (pole)	                  & 0.440$\pm$0.012, 0.370$\pm$0.015 \\
$r_1, r_2$  (side)	                  & 0.478$\pm$0.013, 0.398$\pm$0.017 \\
$r_1, r_2$  (back)	                  & 0.539$\pm$0.014, 0.484$\pm$0.026 \\
\hline
\end{tabular}
\end{center}
$\ast$ photometric + reddening estimate uncertainty. \\
$\ast \ast$ error calculated from Wilson code. As a photometric uncertainty, this should be about 200K.\\
~\\
\centerline{Spot Parameters}
\begin{center}
\begin{tabular}{ccccc}
\hline
STAR& Colatitude (\deg)&Longitude (\deg)&Spot Radius (\deg)&Temp. Factor\\
\hline
2  &   7.5$\pm$1.5   &     45.3$\pm$14.5  &   53$\pm$22   &       0.82$\pm$0.31 \\
\hline
\end{tabular}
\end{center}
\end{table}
 

\references

Cox, A.N., 2000, {\it Allen's Astrophysical Quantities}, AIP Press (Springer), New York

Bradstreet, D. H., 2002, {\it BAAS}, {\bf 34}, 1224

Hubscher, J., Paschke, A. and Walter, F., 2006, {\it IBVS}, 5731 

Hubscher, Paschke, Walter, F., 2007, {\it IBVS}, 5761

Van Hamme, W. V., \& Wilson, R.E, 1998, {\it BAAS}, {\bf 30}, 1402

Wachmann, A. A., 1964, {\it Astron. Abh. Hamburg Sternw.}, {\bf 6}, 179

Wilson, R. E. \& Devinney, E. J., 1971, {\it ApJ}, {\bf 166}, 605

Wilson, R. E., 1990, {\it ApJ}, {\bf 356}, 613

Wilson, R. E., 1994, {\it PASP}, {\bf 106}, 921

Zejda, B.M., 2004,  {\it IBVS}, 5583

\endreferences

\end{document}

