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\IBVShead{5527}{10 May 2004}

\IBVStitle{V802 Aquilae: A Dwarf AW UM\lowercase{a}-Type Binary System}


\IBVSauth{Samec, Ronald G.$^{1,3}$; Martin, Matthew$^1$; Faulkner, Danny R.$^{2,3}$}

\IBVSinst{Astronomy program, Department of Physics and Engineering, Bob Jones University, Greenville, SC 29614 USA; e-mail: rsamec@bju.edu}
\IBVSinst{University of South Carolina, Lancaster, SC 29614 USA; e-mail: DRFaulkn@GWM.SC.EDU}
\IBVSinst{Visiting Astronomer, Cerro Tololo InterAmerican Observatory, Chile}

\SIMBADobj{V802 Aql}

\begintext

In a recent IBVS note, Van Cauteren's (2001) presented crucial, but unfiltered
light curves of V802 Aql [GSC 5119 948, $\alpha(2000)$ = 18\hr 58\mm 54\fsec8, $\delta(2000)$ = $-$03\deg01\arcm11\farcs5]. They show a shallow eclipse 
curve with an amplitude of only 0.35 mags, yet there was a total eclipse of 
long duration (0.1 phases). These characteristics reveal an extreme mass 
ratio system in a state of over contact like AW UMa and V902 Sgr. Such 
binaries may be in their final phases of coalescence into a single 
FK Comae/Blue Straggler-type stars. Also V802 Aql has a period of only 
0\fday2677, making it the smallest of this rare group of binaries.  
Consequently, we included it as an important target on our observing run at 
CTIO in Chili. Our B,V,R,I light curves were taken at  using a 0.9-m reflector
with the CFIM T2K CCD camera (quad mode) and standard $UBVR_cI_c$ filters. 
The observations were taken by RGS and DRF on 6,7 and 9 June 2002; 130 in B, 
160 in V, 147 in Rc, and  148 in Ic in the Johnson-Cousins system.

The stars GSC 5119 964 ($\alpha(2000)$ = 18\hr 58\mm 55\fsec0, $\delta(2000)$ = $-$03\deg02\arcm52\arcs) and \\
GSC~5119~358 ($\alpha(2000)$ = 18\hr 58\mm 45\fsec9, $\delta(2000)$ = $-$03\deg04\arcm25\arcs) were used as comparison and check stars, respectively. 
A finding chart of V802 Aql (V), the comparison (C) and check star (K) are 
given in Figure 1. The light curves and color curves of the variable are given
in Figure 2 as normalized flux versus phase. In addition to the 
characteristics mentioned above, our curves display a depressed primary 
maxima, (0.06 mag in B), suggesting the presence of heavy spot activity 
which would drive the coalescence via magnetic breaking.              
 
\vspace*{-1.1cm}

\IBVSfig{10cm}{5527-f1.eps}{}
\IBVSfigKey{5527-f1.eps}{V802 Aql}{finding chart}

\IBVSfig{10cm}{5527-f2.ps}{}
\IBVSfigKey{5527-f2.eps}{V802 Aql}{light curve}

\IBVSfig{10cm}{5527-f3.ps}{}
\IBVSfigKey{5527-f3.eps}{V802 Aql}{light curve}

Three mean epochs of minimum light were determined from U,B,V,R,I eclipse timing using parabola fits:
\begin{center}
\begin{tabular}{l@{=}c@{$\pm$}l}
HJD MIN I  & 2452432.7562 & 0.0002\\
HJD MIN II & 2452431.8216 & 0.00081\\
           & 2452434.8976 & 0.0011\\
\end{tabular}
\end{center}

We calculated the following linear ephemeris from our observations:
\begin{equation}
{\rm HJD\ Tmin\ I} = 2452432.7571(2) + 0.267532 \pm 0.000042\ {\rm d} \times {\rm E},
\end{equation}
A linear fit to all available timings of minimum light gave: 
\begin{equation}
{\rm HJD\ Tmin\ I} = 2452432.7570(4) + 0.26769479 \pm 0.00000011\ {\rm d}\times{\rm E}
\end{equation}
Equation 1. is not consistent with Equation 2. and may indicate that the 
period is decreasing.  This is the expected scenario, since the period should 
decrease as the mass ratio becomes more extreme.  

Photometric spectral types have been determined from standard star 
observations on the June 9 2002. V802 Aql is of K0 to K2V type, its comparison 
star is G8 to G9V type ($V=12.645\pm 0.008,\ B-V =0.762\pm 0.006$) and the 
check star is G9 to K2V type ($V = 13.418\pm 0.006,\ B-V = 0.842\pm 0.007$). 
The $V$ and $B-V$ magnitudes for the variable was 12.547$\pm$0.003 and 0.810$\pm$0.004 at phase 0.25 and 12.860$\pm$0.004, and 0.827$\pm$0.004 at phase 0.5, 
respectively. From this we fixed the surface temperature of the more massive 
component in light curve synthesis to be 5000 K. 

Our preliminary Binary Maker 2.0 (Bradstreet, 1992) fits gave a mass ratio of 
0.16.  The results of the modeling provided input parameters for a complete 
simultaneous 5 color synthetic light curve solutions with the Wilson Code 
(Wilson \& Devinney, 1971; Wilson, 1990, 1994). Our curves have not been 
transformed to the standard system but experience has shown that this 
introduces only minor changes in the models. Our results include a secondary 
temperature of 5120 K making the system, surprisingly, of W-type. 
The Roche-lobe fill-out was 30\% and the mass ratio was 0.1608 $\pm$ 0.0002. 
The spotted region had a colatitude of 67\deg, a longitude of 281\deg, a spot 
radius of 20\deg\  and a temperature factor of 0.918. The spot was modelled on 
the more massive component.  Our solution is shown overlaying the data in 
Figure 1. A geometrical representation of V802 Aql is given in Figure 3. 

We would expect that the period is undergoing a constant decrease and the 
mass ratio is becoming more extreme.  Plate archival searches and future 
monitoring of this system are needed to confirm the behavior of the system's 
orbital period. 

\IBVSfig{10cm}{5527-f4.eps}{}
\IBVSfigKey{5527-f4.eps}{V802 Aql}{}

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

\references 

Bradstreet, D. H., 1992, {\it BAAS}, {\bf 24}, 1125

Van Cauteren, P. and Wils, P., 2001, {\it IBVS}, 5057

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

\endreferences

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