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\input ibvs2.sty
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\IBVShead{4800}{15 November 1999}

\IBVStitletl{Photometry of the Eclipsing Binary Star}{ GSC\,0008\_324 = 1RXS J001309+053550}

\IBVSauth{R.M. ROBB$^1$, J. Wagg, A. Berndsen, and L. Desroches}

\IBVSinst{Guest User, Canadian Astronomy Data Centre, which is operated by
the Herzberg Institute of Astrophysics, National Research Council of
Canada}

\IBVSinsto{Climenhaga Observatory, Dept.\ of Physics and Astronomy, 
University of Victoria, Victoria, BC, Canada, V8W 3P6, 
e-mail: robb@uvic.ca}

\IBVSabs{ GSC 0008 324 is a near contact eclipsing binary star with deep eclipses and an orbital period of 0.30855 days.}

\SIMBADobj{GSC 0008-324}

\IBVStyp{ EB }

\IBVSkey{ stars: activity}
\IBVSkey{ binaries: close}
\IBVSkey{ binaries: eclipsing}

\begintext

The star GSC 0008\_324 (Jenkner et al., 1990) was found to have Ca H\&K
emission in a survey by Beers et al.\ (1994). Also called 1RXS J001309+053550, it was found to have significant X-Ray emission in a survey by the ROSAT satellite (Bade et al., 1998). In a survey of high proper motion stars it was classified as a K4-5 star by Stephenson (1986). Robertson and Hamilton (1987) measured $V = 10.59$, $B-V = 1.20$ and $V-I = 1.43$.

\IBVSfig{6.5cm}{4800-f1.eps}{Finder chart labeled with the GSC numbers.}

Plotted in Figure 1 is the field of stars observed with the automated 0.5-m telescope and reduced in a fashion identical to that described in Robb et al.\ (1997). Tabulated in Table 1 are the star's identification numbers, coordinates (J2000) and magnitudes from the Hubble Space Telescope Guide Star Catalog (GSC) (Jenkner et al., 1990). Our differential $\Delta R$ magnitudes are calculated in the sense of the star minus GSC\,0008\_789. For each star the mean of the nightly means is shown as $\Delta R$ in Table~1. The standard deviation of the nightly means is a measure of the night to night variations and is called ``Std Dev Between" in Table~1. Brightness variations during a night were measured by the standard deviation of the differential magnitudes during a night. The best night is tabulated in Table 1 as ``Std Dev Within". The star GSC\,0008\_324 had obvious variations during a night and is thus a new eclipsing binary star.

\begin{table}
\caption{Stars observed in the field of GSC\,0008\_324}
\begin{center}
\begin{tabular}{ccccccc}
\hline
\lower6pt\hbox{GSC No.} & R.A. & Dec. & GSC & $\Delta R$ & Std Dev & Std Dev \\[-3pt]
& J2000&J2000 & Mag. & Mag. & Between & Within \\
\hline
0008\_324&$00\hr13\mm09\sec$&$+05\deg$35\arcm47\arcs&10.3&0.913&0.019&0.067\\ 
0008\_789&$00\hr12\mm50\sec$&$+05\deg$37\arcm39\arcs& 9.9& ---   & ---   & --- \\
0008\_743&$00\hr13\mm05\sec$&$+05\deg$37\arcm53\arcs&11.4&1.872&0.007&0.005\\
0008\_949&$00\hr13\mm04\sec$&$+05\deg$34\arcm56\arcs&11.6&2.303&0.012&0.007\\
0008\_754&$00\hr12\mm53\sec$&$+05\deg$34\arcm02\arcs&13.8&4.789&0.005&0.024\\
0008\_865&$00\hr13\mm11\sec$&$+05\deg$35\arcm40\arcs&14.2&5.179&0.018&0.034\\
\hline
\end{tabular}
\end{center}
\end{table}

There is no ambiguity in the determination of the orbital period of 
GSC\,0008\_324 since three of the nights included more than one cycle. Using data points within 0\fday02 of the minimum, and the method of Kwee and van Woerden (1956), the heliocentric Julian Dates of minimum were found and are tabulated in Table~2. On some nights observations were made in more than one color and the separate times of minima are indicated.

\begin{table}[h]
\caption{Times of Minimum ($-\,2451400$) of GSC\,0008\_324}
\begin{center} 
\begin{tabular}{lllll}
\hline
JD & JD & JD & JD & JD \\
\hline
51.8770 $R$ & 54.9620 $R$ & 55.8858 $I$ & 60.9756 $I$ & 61.9009 $R$ \\
53.8792 $R$ & 55.7301 $I$ & 55.8883 $V$ & 60.9758 $B$ & 74.7081 $R$ \\
54.8043 $R$ & 55.7302 $V$ & 60.8232 $I$ & 61.7499 $R$ \\
\hline
\end{tabular}
\end{center}
\end{table}

A fit to these times gives the ephemeris:
$$
{\rm HJD~of~Minima} = 2451451\fday 7204(7) + 0\fday30855(3) \times E.
$$
where the uncertainties in the final digit are given in brackets and the mean square error of the fit is 0\fday0016.

The differential (GSC\,0008\_$324-GSC$\,0008\_789) $R$ magnitudes phased at this period are plotted in Figure~2 with different symbols for each of the nights. The asymmetry in the maxima is indicative of star spots, distributed asymmetrically over the surface of the star(s). 

CCD frames of the field were obtained with $B$, $V$ and $I_C$ filters to ascertain the temperature and brightness of the variable star. The star GSC\,0008\_789 has $B$ and $V$ magnitudes measured by the Hipparcos satellite (ESA 1997) to be $V_T = 9.832\pm.032$ and $(B-V)_T = 1.412 \pm .083$. Measurements of GSC\,0008\_324 relative to this star give $V=10.64\pm.05$ and $B-V= 1.07\pm.20$ at maximum light. This $(B-V)$ is in agreement with the measurements of the Hipparcos satellite (ESA 1997) and also with Robertson and Hamilton (1987). From this color we estimate the spectral class of GSC\,0008\_324 to be approximately K4V (Cousins 1981) in agreement with Stephenson (1986).

\IBVSfig{8.75cm}{4800-f2.ps}{$R$ band light curve of GSC\,0008\_324 for 1999}

\IBVSfig{9.5cm}{4800-f3.eps}{$R$ band normal points with curve from an example  model of the eclipsing system}

\vskip-22pt
The light curve leads us to expect this to be a near-contact system. Using Binmaker 2.0 (Bradstreet 1993), an example model light curve was made, assuming the temperature of the hot star to be 4300~K the mass ratio of 0.83 and the latitude of the spot of $0\deg$. The data are best fitted with an inclination of $71\deg$ and relative radii of 0.36 and 0.38. The temperature of the cool star was adjusted to 3650~K and a spot $20\deg$ in radius at a longitude of $270\deg$ was added to get the fit seen in Figure~3. Considering the cycle to cycle variations seen in the light curve, this is a satisfactory fit. The uncertainty in the inclination is about $\pm3\deg$ and the difference in temperature and spot diameter are known to about $\pm10\%$.

\IBVSfig{3.5cm}{4800-f4.ps}{Three-dimensional model of the near-contact system at phase 0.75}
 
The relative sizes and shapes of the components of the system and the spot
are shown in Figure~4, again using Binmaker 2.0 (Bradstreet 1993).

The star GSC\,0008\_324 is therefore a near-contact eclipsing system with late-type components and at least one spot. Photometric observations should be continued to monitor light curve changes due to spot migration, flares, and period changes. Spectroscopic observations have been started to determine a precise spectral class for the system and to measure radial velocities to determine the masses and the scale of the system. 

\references

Beers, T. C., Bestman, W. and Wilhelm, R., 1994, {\it AJ}, {\bf108}, 268

Bade, N., Engels, D., Voges, W., Beckmann, V.,  Boller, Th.,  Cordis, L.,
Dahlem, M., Englhauser, J., Molthagen, K., Nass, P., Studt, J., Reimers, D., 1998, {\it A\&A Sup.}, {\bf 127}, 145

Bradstreet, D.H., 1993, Binary Maker 2.0 User Manual, Contact Software,
Norristown, PA 19401-5505, USA

Cousins, A.W., 1981, {\it SAAO Circ.}, {\bf 6}, 4

ESA, 1997, The Hipparcos and Tycho Catalogues, ESA SP-1200

Jenkner, H., Lasker, B., Sturch, C., McLean, B., Shara, M., Russell, J., 1990, {\it AJ}, {\bf 99}, 2082

Kwee, K.K., van Woerden, H., 1956, {\it BAN}, {\bf 12}, 327

Robb, R.M., Greimel, R., Ouellette, J., 1997, {\it IBVS}, No.\,4504

Robertson, T.H., and Hamilton, J.E., 1987, {\it AJ}, {\bf 93}, 959

Stephenson, C.B., 1986, {\it AJ}, {\bf 92}, 139

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