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\input ibvs2.sty

\begin{document}

\IBVShead{5724}{1 September 2006}

\IBVStitletl{GSC 3576-0170: A New Near-Contact Solar-Type Binary,}{ Period Analysis and Classification}

\IBVSauth{Nelson, R.H.$^1$; Robb, R.M.$^2$; Henden, A.A.$^3$; Krajci, T.$^4$; Quester, W.$^5$}

\IBVSinst{1393 Garvin Street, Prince George, BC, Canada, V2M 3Z1,
e-mail: bob.nelson@shaw.ca}

\IBVSinst{Department of Physics and Astronomy, Univ.\ of Victoria, 
Victoria, B.C., Canada, V8P 5C2,\\ e-mail: robb@uvic.ca}

\IBVSinst{U.S. Naval Observatory, P.O. Box 1149, Flagstaff, AZ, 86002-1149,
USA, e-mail: aah@nofs.navy.mil}

\IBVSinst{P.O. Box 1351, Cloudcroft, NM 88317, USA,
e-mail: tom\_krajci@tularosa.net}

\IBVSinst{Wilhelmstr.\ 96, D-73730 Esslingen, BAV, Germany,
e-mail: wquester@aol.com}

\SIMBADobj{GSC 3576-0170}

\begintext

GSC 3576-0170 (at 20\hr23\mm38\sec, +46\deg 55\arcm52\arcs, J2000.0) was 
discovered to be
variable by one of us (RHN) while doing CCD observations of ZZ
Cyg at his private observatory (see Nelson, 2003) in early June 2003.  
Several stars were included in the aperture photometry to serve
as check stars and one of them displayed the features of an eclipsing
binary.  During that period, RMR obtained a full light curve in $R_C$ (525
points) (see Robb \& Greimel, 1999) and four times of minima.  The light
curves shown in Figure 1 show that the system is a close binary. Since the
maxima are of different height, we expect spots on one or both stars.

\IBVSfig{8cm}{5724-f1.ps}{}
\IBVSfigKey{5724-f1.ps}{GSC 3576-0170}{light curve}

At the USNO Flagstaff Station 1.00-m telescope (see Nelson, 2002), AAH
observed the GSC 3576-0170 and ZZ Cyg field in the standard Johnson--Cousins
$BVR_CI_C$ passbands on 2003-08-10 (UT){}.  This photometry is summarized in
Table 1 with magnitude errors, in millimagnitudes, appearing in brackets.

\begin{table}
\begin{center}
\caption{Positions and magnitudes}
\vskip 2mm
\begin{tabular}{lcccccc}
\hline
Star & GSC       & Phase & $V$ & $B-V$ & $V-R_C$ & $R_C-I_C$ \\
\hline
Var  & 3576-0170 & 0.39&12.496(5)& 0.737(3)&0.438(3)& 0.398(5)\\
Var  & 3576-0170 & 0.68&12.484(5)& 0.735(3)&0.432(3)& 0.411(5)\\
C    & 3576-0964 & na           & 11.014(3)&0.138(6)&0.090(1)&0.100(2)\\
K    & 3576-0702 & na&11.561(6)  & 0.432(8)&0.265(4)& 0.256(5)\\
\hline
\end{tabular}
\end{center}
\end{table}

All known times of minima were collected (Table 2) and an $O-C$ plot
constructed (Fig.~2).


\begin{table}
\begin{center}
\caption{Observed minima of GSC 3576-0170}
\vskip 2mm
\begin{tabular}{llccrr}
\hline
Observer & HJD${}-{}$ & Error & Type & Cycle & $O-C$ \\
         &2400000     & (days)&      &       &   (days)\\
\hline
Nelson  & 52794.863  & 0.0040 & II & $-2.5$   &  0.0009\\
Nelson  & 52795.8716 & 0.0005 & I  & 0\phantom{.0}      & $-0.0030$\\
Robb    & 52799.9230 & 0.0005 & I  & 10\phantom{.0}     & $-0.0016$\\
Quester & 52802.554  & 0.0020 & II & 16.5   & $-$0.0032\\
Robb    & 52806.8076 & 0.0003 & I  & 27\phantom{.0}     & $-0.0021$\\
Robb    & 52807.821  & 0.0010 & II & 29.5   & $-$0.0012\\
Quester & 52812.478  & 0.0020 & I  & 41\phantom{.0}     & $-0.0018$\\
Nelson  & 52826.860  & 0.0010 & II & 76.5   &  0.0025\\
Krajci  & 53263.8659 & 0.0005 & II & 1155.5 &  0.0081\\
Krajci  & 53264.6735 & 0.0002 & II & 1157.5 &  0.0057\\
Robb    & 53305.7787 & 0.0004 & I  & 1259\phantom{.0}   &  0.0029\\
Krajci  & 53837.9506 & 0.0002 & I  & 2573\phantom{.0}   & $-0.0018$\\
Krajci  & 53852.937  & 0.0002 & I  & 2610\phantom{.0}   & $-0.0006$\\
Krajci  & 53900.7278 & 0.0002 & I  & 2728\phantom{.0}   & $-0.0004$\\
Robb    & 53939.8099 & 0.0005 & II & 2824.5 & $-0.0012$\\
Robb    & 53941.8337 & 0.0004 & II & 2829.5 & $-0.0025$\\
Robb    & 53943.8605 & 0.0008 & II & 2834.5 & $-0.0007$\\
\hline
\end{tabular}
\end{center}
\end{table}

Assigning equal weights, the following ephemeris (in days) was obtained,
and the above tabular $O-C$ values were calculated from the linear least
squares best fit relation:
$${\rm Min.~I = HJD}~24 52795.8746(22)  +   0.40500(1) \times E.$$

\IBVSfig{8cm}{5724-f2.ps}{}
\IBVSfigKey{5724-f2.ps}{GSC 3576-0170}{O-C diagram}

\IBVSfig{8cm}{5724-f3.ps}{}
\IBVSfigKey{5724-f3.ps}{GSC 3576-0170}{spectrum}

\vspace{-24pt}
It is clear from Figure 2 that deviations from the line of best fit far
exceed the internal error estimates and we suspect there is some
systematic effect(s).  A quadratic fit can be invoked; however that still
leaves the rms error at 0.0020 days.  Clearly more times of minima are
required to sort out the true period and any period variation and we will
reserve a full discussion of the subject to a future paper. Therefore
although the period is quoted to five figures, the last figure is
uncertain. The error in the period has been estimated by the difference in
period between the period obtained from the first (2003) and second (2004)
groups of data only, and the period from all the data.

A spectrum of GSC 3576-0170 observed with 1.8-m telescope of the Herzberg
Institute of Astrophysics (by RMR) is shown in Figure 3.  The dispersion
was 0.96 \AA\ per pixel. By comparing the H$\gamma$ to the FeI 4384 and the H$\delta$ to the CaI 4227
lines we classify this star as G1V with an uncertainty of one sub class.
Therefore we estimate its temperature to be 5865 K (Cox, 2000).

Wilson--Devinney modelling (Wilson \& Devinney, 1971) was attempted, but
since (based on the low depths of the minima) the eclipses were obviously
partial, it was not possible to determine the mass ratio based on
photometric data alone (Terrell \& Wilson, 2005).

Nevertheless, modelling runs were made for a range of mass ratios using
detached, overcontact, semi-detached with a bright spot on star 2, and
double contact.  However, detached consistently gave smaller residuals by
10% or more.  The mass ratio $q = M_2/M_1$ was assumed to lie in the range
$0.15 < q < 0.35$ (because of steeply rising residuals outside this range)
giving an inclination in the range of 65--70°.  The temperature of the
secondary is 4800-4900 K, giving it a spectral type of K2 $\pm$ one
subclass. One G1V and one K2V star would have an absolute magnitude of $V =
4.37$ with a $(B-V)_0$ of 0.67.  Therefore the reddening or colour excess,
$E(B-V) = (B-V)-(B-V)_0$ would be 0.07 and, assuming an $R$ of 3.0, the
absorption would be $A_V = 0.21$ and the distance becomes approximately 400
parsecs.

{\bf Acknowledgements.}
Thanks are due to Environment Canada for the website satellite images (see
Satellite images below) that were essential in predicting clear times
for observing runs in this cloudy locale. Thanks are also due to Attilla
Danko for his Clear Sky Clocks, (see below).

\references

Cox, A.N., ed., 2000, Allen's Astrophysical Quantities, 4th ed., (Athlone
Press, London)

Danko, A., Clear Sky Clocks, http://cleardarksky.com/

Nelson, R.H. et al., 2002, {\it IBVS}, No.\ 5228

Nelson, R.H., 2003, {\it IBVS}, No. 5371

Robb, R.M., Greimel, R., 1999, {\it ASP Conf.\ Ser.}, 189, 198

Satellite images for North America,
http://www.cmc.ec.gc.ca/cmc/htmls/satellite.html

Terrell, D., Wilson, R.E., 2005, {\it Ap\&SS}, 296, 221

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

\endreferences

\bigskip
\bigskip
\bigskip

\IBVSerrata{5557, 5586}

Sebastian Otero reported the following errors:

\begin{table}[h!]
\begin{tabular}{c l l l}
\hline
IBVS No. & item & printed & correct \\
\hline

5557 & identifier (NSV 233) & GSC 0013-0919 & GSC 0013-0976 \\

5586 & filter (NSV 15024) & 13.20(12.80) & 13.20(12.80)* \\

\hline
\end{tabular}
\end{table}

\end{document}
