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\IBVShead{5786}{14 August 2007}
 
\IBVStitletl{V963 Cygni is an Active Detached Binary}{ with a 33.5 Hour Period}

\IBVSauth{SAMEC, RONALD G.$^{1,4}$; BRANNING, JEREMY$^1$; JONES, STEPHANIE M.$^1$; FAULKNER, DANNY R.$^{2,4}$; HAWKINS, NATHAN C.$^{3,4}$; VAN HAMME, WALTER$^5$}

\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}
\IBVSinst{Florida International University, Miami, Florida}

\SIMBADobj{V963 Cyg}

\begintext

   As a part of our study of observationally neglected eclipsing binaries we observed the eclipsing binary V963 Cygni, 
[GSC 2656-1995, $\alpha$(2000) = 19\hr 44\mm 4\fsec92,  $\delta$(2000) = 31\deg 41\arcm 50\farcs2].  Wachmann (1961) discovered this variable 
and reported 21 times of minimum light and the ephemeris 
\begin{equation}           
                   {\rm HJD\ Tmin\ I} = 2434629.397 + 0.6973{\rm d\times E}.
\end{equation}           

From his photographic light curves he classified this as an Algol. Sixteen subsequent times of minimum light have appeared 
in the literature (Saf\'ar and Zejda 2000, and 2002, Agerer and H\"ubscher 2000, Dvorak 2005, H\"ubscher 2005, H\"ubscher, Paschke, 
and Anton 2005, H\"ubscher, Paschke, and Walter 2005 and 2006, H\"ubscher, Paschke, and Walter 2006, 
H\"ubscher and Walter 2007). 
  
   Our $UBVRI$ light curves were taken on 19-25, July, 2004 by NCH, RGS, and DRF with the Lowell 31 inch reflector in 
Flagstaff, AZ through the National Undergraduate Research Observatory (NURO).  The CCD camera was liquid nitrogen 
cooled, and the chip was a metachrome coated TEK 512$\times$512.  Sixty-nine observations were taken in $U$, 94 in $B$, 125 in $V$, 
105 in $R$ and 96 in $I$.  Our observations, variable minus comparison delta
magnitudes are given in electronic Table~1 (available through the IBVS-website as {\tt 5786-t1.txt}).  The stars 
[GSC 2656-3363, $\alpha$(2000) = 19\hr 44\mm 03\fsec64, $\delta$(2000) = 31\deg41\arcm 13\farcs3], and [GSC 2656-2055, $\alpha$(2000) = 19\hr 44\mm 16\fsec91, $\delta$(2000) 
= 31\deg41\arcm 31\farcs6], were used as comparison and check respectively.  A finding chart of V963 Cyg (V), the comparison (C), 
and the check star, (K) are given in Figure~1.

\IBVSedata{5786-t1.txt}
\IBVSdataKey{5786-t1.txt}{V963 Cyg}{}

\IBVSfig{10cm}{5786-f1.ps}{Finder Chart, V963 Cygni, comparison (C) and Check (K). V' is V965 Cygni.}
\IBVSfigKey{5786-f1.ps}{V963 Cyg}{finding chart}

Early in the observing run we discovered that the two consecutive deep eclipses were of different depths, $\sim 0.78$ and $\sim 0.67$ magnitudes in $V$, 
respectively. There was no hint of a shallow secondary eclipse as expected in an Algol light curve.  Rather, there is a 
fairly flat maximum between the eclipses. Evidently this system had been mistakenly classified.  Instead of two dissimilar 
stars in a semidetached mode, there are two similar stars in a detached configuration. The period, consequently, needs 
to be doubled. Three mean epochs of minimum light were determined from $UBVRI$ timings of one primary and two secondary eclipses, 
${\rm HJD\ I} = 2453207.7686 \pm 0.003,$ ${\rm HJD\ II} = 2453209.8607 \pm 0.0010, 2453211.9540 \pm 0.0031$.  The following ephemeris reflects this finding:
\begin{equation}	
{\rm HJD\ Tmin\ I} = 2453209.8609 \pm 0.0007 + 1.39466785 \pm 0.00000016 {\rm d\times E}.
\end{equation}

This was arrived at from 38 available times of minimum light (including ours) covering some 15000 orbits. Very recent timings seem to 
be forming a pattern, possible a negative parabola, but further observations are needed to verify the effect. All times of minimum light are 
shown in electronic Table~2 (available through the IBVS-website as {\tt 5786-t2.txt}). The next equation was calculated by the ephemeris option of the Wilson code (van Hamme and Wilson, 1998):
\begin{equation}
{\rm HJD\ Tmin\ I}=2453209.8585 \pm 0.0003 + 1.3945 \pm 0.0002{\rm d\times E.}.
\end{equation}   

\IBVSedata{5786-t2.txt}
\IBVSdataKey{5786-t2.txt}{V963 Cyg}{}

   Standard magnitudes were calculated from our observations and 6 and 7 Landolt standard stars taken on July 20 and 24, respectively. 
They reveal that V963 Cyg is of spectral type F6.5 $\pm$ 1.0.  Values for the comparison and check star 
are both F5 $\pm$ 0.5.  Our standard magnitudes and color indices are
given in electronic Table~3 (available through the IBVS-website as {\tt 5786-t3.txt}).  

\IBVSedata{5786-t3.txt}
\IBVSdataKey{5786-t3.txt}{V963 Cyg}{}

   A $UBVRI$ synthetic solution was calculated. We first used Binary Maker 3.0 (Bradstreet, 2002) to provide 
an initial fit to each of the $V, R$, and $I$ light curves.  The fits were all detached.  The main difficulty encountered in 
fitting the light curves were the irregularities in the out-of-eclipse portions, which evidently is due to several large 
spot regions.  Thus, V963 Cyg has strong magnetic activity. 
The eclipse shoulders have somewhat different shapes in each effective 
wavelength. Particularly, the $R$ curve 
is much different from the $B$ curve in the shoulder of the secondary eclipse.  This is believed be due to roving star magnetic spots
arising from nonsynchronous rotation of each component. Our Binary Maker fits all gave a mass ratios of about 0.9. 

   Using our starting values, we proceeded to compute a simultaneous five color light curve solution with the updated 
Wilson Code (Wilson and Devinney, 1971; Wilson, 1990, 1994; Van Hamme and Wilson, 1998), which includes Kurucz stellar 
atmospheres, rather than black body, and a detailed reflection treatment along with 2-D limb darkening coefficients.  
The main mode of calculation is differential corrections.
In addition to spot modeling, we tried adjusting the F parameter (non-synchronous rotation, Wilson 1979, Limber 1963), and third-light. It was found
that the F parameter is the key to successfully modeling of the system. The system is evidently young and the stars are not
yet gravitationally locked. This gives further evidence that the period is $\sim 1.4$d rather than $\sim 0.7$. An 0.7 day system in a
nonsynchronous orbit would be exceptionally rare.  Our solution indicates that the binary is a detached system with a mass ratio, 
$m_2/m_1 \sim 0.9$.  The component temperature difference was only about 300 K. The solution reported here has 2 large 
spot regions.  This indicates the magnetically active nature of this binary. The light curve solutions are given in 
electronic Table~4 (available through the IBVS-website as {\tt 5786-t4.txt}), and the calculated synthetic light curves are shown overlying the normalized light curve in Figure~2 and 3.  
The star surfaces are shown in Figure~4 (from Binary Maker). 
Due to the fact that the eclipses are partial, our model 
is preliminary. But a mass ratio near one is strongly suggested due to 
the deep and fairly equal eclipse depths.
 Radial velocity curves are needed for a complete 
solution.  In this regard, we note here that errors given in the table are model dependent standard errors.

\IBVSedata{5786-t4.txt}
\IBVSdataKey{5786-t4.txt}{V963 Cyg}{}

\IBVS2fig{7.5cm}{5786-f2.ps}{$UBVRI$ Light curves compared with WD solution.}{5786-f3.ps}{$UBVRI$ Light curves compared with WD solution.}
\IBVSfigKey{5786-f2.ps}{V963 Cyg}{light curve}
\IBVSfigKey{5786-f3.ps}{V963 Cyg}{light curve}

\IBVSfig{8cm}{5786-f4.ps}{Star surfaces, V963 Cygni.}
\IBVSfigKey{5786-f4.ps}{V963 Cyg}{}

\newpage

   We wish to thank NURO for their allocation of observing time, and a small research grant from the American Astronomical 
Society and an Arizona Space Grant which supported this observing run.   

\references

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

Dvorak, S.W., 2005, {\it IBVS}, 5603

H\"ubscher, J., 2005, {\it IBVS}, 5643	

H\"ubscher, J., Paschke, A., \& Walter, F., 2005, {\it IBVS}, 5657	

H\"ubscher, J., Paschke, A., \& Walter, F., 2006, {\it IBVS}, 5731	

H\"ubscher, J. \& Walter, F., 2007, {\it IBVS}, 5761

Limber, D.N., 1963, {\it ApJ}, {\bf 138}, 1112

Saf\'ar, J., Zejda, M., 2000, {\it IBVS}, 4888

Saf\'ar, J., Zejda, M., 2002, {\it IBVS}, 5263

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

  Wachmann, A. A. 1961, {\it Astron. Abh. Hamburg. Sternw.}, {\bf 6}, 1

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

Wilson, R. E., 1979, {\it ApJ}, {\bf 234}, 1054

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

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

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