\documentstyle[epsfig,twoside]{article}

\input ibvs2.sty

\begin{document}
\IBVShead{5231}{31 January 2002}

\IBVStitle{GSC 0983.1044: A SHORT-PERIOD RS CV\lowercase{n} BINARY}


\IBVSauth{Kaiser, D.H.$^1$;  Pullen, A.C.$^2$; Henden, A.A.$^3$; Baldwin, M.E.$^4$; Guilbault, P. R.$^5$;\\ \indent Hager, T.$^6$; Terrell, D.$^7$}

\IBVSinst{2631 Washington Street, Columbus, Indiana 47201, USA,
e-mail: dhkaiser@sprynet.com}

\IBVSinst{10215 Davis Road, P.O. Box 930, Wilton, California
95693, USA, e-mail: cpullen@pacsafe.com}

\IBVSinst{Universities Space Research Association/U.S. Naval
Observatory, P.O.Box 1149, Flagstaff, \\ \indent Arizona
86002-1149, USA, e-mail: aah@nofs.navy.mil}

\IBVSinst{8655 N. Co. Road. 775E, Butlerville, Indiana 47223, USA,
e-mail: mbald00@hsonline.net}

\IBVSinst{P.O. Box 287, Chepachet, Rhode Island 02814, USA,
e-mail: pete1199@aol.com}

\IBVSinst{34 Mount Tom Road, New Milford, Connecticut 06776, USA,
e-mail: thager@pcnet.com}

\IBVSinst{Department of Space Studies, Southwest Research
Institute, 1050 Walnut Street, Suite 426, Boulder, \\ \indent
Colorado 80302, USA, e-mail: terrell@boulder.swri.edu}

\IBVSabs{We report on the nature of GSC 0983.1044}

\SIMBADobj{GSC 0983-1044}

\IBVStyp{ RS CVN }

\begintext

M. Baldwin, chairman of the AAVSO eclipsing binary committee,
initiated an observing program to study stars from the ROTSE 1 sky
survey (Akerlof et al., 2000). Baldwin chose those stars that were
likely eclipsing binaries and did not appear elsewhere in the
literature.  Once eclipses were confirmed visually, he asked AAVSO
CCD observers to time eclipses and to construct accurate light
curves so that periods, types and amplitudes could be defined.

One such star, GSC 0983.1044 = ROTSE 1 J165241.80 +124905.2, was
listed in the ROTSE catalogue as a 13$^{th}$ magnitude eclipsing
star with a period of 0\fday 40763 and an amplitude of 1.022
magnitudes. After eclipses were confirmed visually by Baldwin,
Henden used the USNO1.0-m telescope with a SITe 1024 $\times$ 1024 thinned,
backside illuminated CCD and Johnson-Cousins $BVR_{c}I_{c}$
filters along with Landoldt standards to determine standard
magnitudes for the variable at maximum and comparison stars. These
data are gathered in Table 1 and the errors in the last decimal
place are given in parenthesis. GSC 0983.1313 was chosen as the
comparison and GSC 0983.0566 as the check star. Astrometry is
based on USNO-A 2.0 and has less than 100mas internal errors.

{\small
\begin{center}

{\normalsize Table 1. Standard magnitudes and color
indices,Henden} \vskip2mm
\begin{tabular}{cccccccc}
\hline

Star & GSC & RA & DEC &$V$ & $B-V$ & $V-R_{c}$ & $R_{c}-I_{c}$\\
\hline
Variable$^1$ & 0983.1044 &  16:52:41.80 & +12:49:05.3 & 12.901(1) & 0.775(3)& 0.460(2)& 0.438(3)\\
Comparison & 0983.1313 & 16:52:33.70 & +12:47:37.9 & 13.015(1)& 0.627(2) & 0.380(2) & 0.366(4)\\
Check &0983.0556 & 16:52:19.09 & +12:50:44.2 & 12.218(1) & 0.943(3)& 0.534(2)& 0.431(3)\\
\\
\begin{tabular}{l p{13cm}}
{\small $1$ = at phase 0.11 }\\
\hline
\end{tabular}
\end{tabular}
\end{center}
}

More complete photometric information about all stars within 5
arcmin of the variable can be found in 5231-t4.txt at the $IBVS$
website.

\IBVSedata{5231-t4.txt}

Pullen observed GSC 0983.1044 with his 0.28-m SCT + ST-6 CCD + $V$
filter.  Kaiser used his 0.35-m SCT + ST-9E CCD + $V$ filter.  A
total of 6 times of minimum were obtained.

Guilbault and Hager visited the Harvard College Observatory and
examined 58 blue-sensitive plates. Observations were made by eye,
using a sequence of steps to estimate the changes in brightness.
Two instances of faint light were found.

\begin{center}

{\normalsize Table 2. Times of minimum, GSC 0983.1044} \vskip2mm
\begin{tabular}{p{1.8cm}p{0.1cm}ccccc}
\hline
\multicolumn{1}{c}{HJD} && Error & Cycle & $O-C$ & Observer     &  Type\\
\multicolumn{1}{c}{2400000\,+} && $+/-$ & Cycle & $O-C$ & Observer     &  Type\\
\hline

45901.652& &      &    $-$7195    & $-$0.002 &  PG/TH & pg\\
46116.891& &      &    $-$6931    & $+$0.001 &  PG/TH & pg\\
51738.7197&$\dagger$& (4)  &    $-$35.5    & $-$0.001  &  ACP    & CCD\\
51740.7594& & (4)  &    $-$33.0    & 0.000 &  ACP    & CCD\\
51747.6883&$\dagger$& (2)  &    $-$24.5    &  $-$0.001  & DHK &CCD\\
51753.8028& & (2)  &    $-$17      & $-$0.001 &  ACP    & CCD \\
51767.6641& & (1)  &      0        & 0.000 &  DHK   &CCD\\
52084.8118& & (1)  &    $+$389     & 0.000 &  DHK   & CCD\\

\begin{tabular}{l p{13cm}}
{\small $\dagger$ Secondary minimum }\\
\hline
\end{tabular}
\end{tabular}
\end{center}

The CCD times of minimum were determined with the software AVE
(Barbera 2000) based on the Kwee and Van Woerden method (Kwee -
Van Woerden 1956). The time of minimum from the Harvard data is
the mid-point of the exposure. A least squares solution with the
CCD minima weighted as 10 and the photographic data as 1 results
in the new elements:

$$ \begin{array}{r@{}r@{}l} {\rm Min.~I = HJD~} 2451767.6637 & {}
+ 0\fday81528987 & {} \times E.\\
\pm 0.0001 & {} \pm 0.00000006\\
\end{array} $$

This period is very close to twice the ROTSE 1 period. All data
are phased to these elements and are shown in Figure 1. The
maximum magnitudes at phases 0.25 and 0.75 differ by 0\fmm07 $V$
suggesting the possibility of spots.  Indeed when Kaiser's year
2000 observations are compared to his 2001 data at phase 0.9, they
differ on the order of 0.04 magnitudes in $V$. Such seasonal
variations are typical of RS CVn binaries.

\IBVSfig{10cm}{5231-f1.eps}{Phased light curve, GSC
0983.1044.}

Solutions to the 2000 light curve using equatorial spots were done with
the Wilson-Devinney light curve program (Wilson and Devinney,
1971; Wilson, 1979; Wilson, 1990). The effective temperature of
the primary (5300 K) was chosen to be consistent with our rough
spectral type estimate based on the outside-eclipse $B-V$ value.
The composite $B-V$ of the system at maximum light is about 0\fmm8
and the monochromatic luminosity ratio in $V$ from our light curve
solution is about 0\fmm6. Although we do not have full light curves
in $B$ to compute the color of the individual components
precisely, it is clear that the $B-V$ of the primary should be a
bit less than 0\fmm8 and the $B-V$ of the secondary should be a bit
more than 0\fmm8. {\it Astrophysical Quantities} (2000) gives a $B-V$
of 0\fmm74 for a G8 $V$ star and a $B-V$ of 0\fmm81 for a K0 star.
Therefore we estimate that the primary is mid-to-late G-type and
the secondary is an early K-type, making the system an RS CVn
binary (Morgan and Eggleton, 1979). A single-spot solution could
not achieve a fit to the light curve, but a two-spot model does
fit reasonably well as seen in Figure 2. The solution indicates
that the system is detached and has large spots on the secondary
component, again indicative of an RS CVn system.

\IBVSfig{10cm}{5231-f2.eps}{The two-spot light curve solution, GSC
0983.1044.}

Table 3 shows the various parameters from the best-fit solution
but with data in only one filter, the parameters should be
considered preliminary, especially the spot parameters as attested
by their large errors. High-precision $UBVRI$ photometry should
enable us to reliably determine the spot parameters (e.g., Samec
and Terrell, 1995) and a radial velocity study would be needed to
confirm that the mass ratio is near unity.

\begin{center}

{\normalsize Table 3. Parameter values and errors for the best-fit
solution} \vskip2mm
\begin{tabular}{cc}
\hline
Parameter &  Value  \\
\hline
$i$ & $89\fdeg$2 $+/-$$0\fdeg$5  \\
$\Delta$ $T$ & 417 K $+/-$88K \\
$q$ & 1.0 (assumed)\\
$\Omega_1$ & 5.71 $+/-$ 0.08\\
$\Omega_2$ & 5.94 $+/-$ 0.05\\
$L_1/(L_1 + L_2)$ & 0.628 $+/-$ 0.13\\
$g_1 = g_2$ & 0.32 (assumed)\\
$A_1 =A_2$ & 0.5 (assumed)\\
Spot 1 longitude & 1.09 rad $+/-$ 0.86\\
Spot 1 radius & 0.85 rad $+/-$ 0.52\\
Spot 1 temperature factor & 0.94 $+/-$ 0.02\\
Spot 2 longitude & 3.58 rad $+/-$ 2.89\\
Spot 2 radius & 0.26 rad $+/-$ 0.31\\
Spot 2 temperature factor & 0.87 $+/-$ 0.19\\

\hline
\end{tabular}
\end{center}

\vskip4mm

We wish to thank Alison Doane, acting Curator of the Astronomical
Photograph Collection at the Harvard College Observatory, for use
of the Harvard Patrol Plates.

\references

Akerlof, C., et al., 2000, {\it AJ}, {\bf 119}, 1901

{\it Allen's Astrophysical Quantities}, 4th edition, A. N. Cox
ed., Springer-Verlag, New York, 2000

Barbera, R., {\tt http://www.gea.cesca.es}

Kwee, K. K., and Van Woerden, H., 1956, {\it BAN}, {\bf 12},
No.\,464, 327

Morgan, J.G., and, Eggleton, P.P, 1979, {\it MNRAS}, {\bf 187},
661

Samec, R.G., and Terrell, D., 1995, {\it PASP}, {\bf 107}, 427

Wilson, R.E., and 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

\end{document}

