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\input ibvs2.sty

\begin{document}

\IBVShead{5381}{24 February 2003}

\IBVStitle{GSC 4288-186: a New Eccentric Binary}

\IBVSauth{Baki\c{s}, V.; Erdem, A.; Budding, E.; Demircan, O.}

\IBVSinsto{\c{C}anakkale Onsekiz Mart University Ulupinar Astrophysics Observatory, TR-17100, \c{C}anakkale, Turkey; email: bakisv@physics.comu.edu.tr}

\SIMBADobj{GSC 4288-0186}

\IBVSkey{stars: eccentric binary}

\begintext


During a campaign of photometry on XX Cep in the summer of 2002,
one of the stars in the field was discovered to be variable by VB.
We observed the star at the \c{C}anakkale Onsekiz Mart
University's Ulupinar Astrophysics Observatory (\c{C}OMU UAO)
(latitude, 40\deg 06\arcm 01\arcs\ North, longitude, 01\hr 45\mm
54\sec\ East, altitude, 410 m). We made the measurements with a
30 cm Meade LX200 Schmidt-Cassegrain telescope at f/10 and f/3.3,
and using an SBIG ST-237 CCD Camera without filters. Exposure
times ranged from 6 to 10 seconds.

\IBVSfig{6cm}{5381-f1.eps}{Identification map of GSC 4288-0186 (bars),
comparison star (No. 1) and check star (No. 2). The size of the
field is 16.6\arcm$\times$12.5\arcm , unfiltered CCD band, 6-seconds
exposure.}
%\IBVSfigKey{5381-f1.eps}{GSC 4288-0186}{finding chart}

The star has been observed over 20 nights to confirm the
variability and  determine the period. The Julian dates of
observations (+2452000) are 515, 535, 536, 537, 538, 539, 540,
551, 552, 553, 555, 571, 575, 576, 577, 579, 591, 593, 594, 602.
Catalogue information for the  variable, comparison and check
stars are given in Table 1. We show the finding chart for the
observed stars in Figure 1.

CCD images were processed by the MUNIDOS photometry software
package (Hroch, 1997). Our differential magnitudes are calculated
in the sense of star minus \hbox{GSC~4288-0241}. Times of minima of the
star were first found using the method of Kwee- van Woerden (1956)
and, depending on the nature of the data set, by the Taranis
programme, which is based on an artificial neural network
(Gaspani, 1995). The times of minima, with their uncertainties,
are presented in Table 2. From these times of minimum light we
find the ephemeris to be:

\vspace {3mm} \centerline{HJD of Primary Minimum =
2452591.2761(1)+5\fday63508(2)$\times$E.} \vspace {3mm}

\noindent where the uncertainties in the final digit are given in
brackets In Figure 2, the differential unfiltered magnitudes
phased at this period are plotted.

\begin{table}
\caption{Stars observed in the field of GSC 4288-0186}
\begin{center}
\begin{tabular}{cccc}
\hline
Type&Star's & R.A. & Dec.\\
    &GSC Id & J2000&J2000\\

\hline

Variable&0186&$23\hr37\mm43\fsec30$&$64\deg$18\arcm11\farcs6\\
Comparison&0241&$23\hr38\mm09\fsec00$&$64\deg$17\arcm56\farcs6\\
Check&0100&$23\hr37\mm55\fsec57$&$64\deg$18\arcm22\farcs3\\


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


\begin{table}
\caption{Times of Minimum Light $-$2400000}
\begin{center}
\begin{tabular}{ccc}
\hline
 HJD      &Error   &Type\\
52515.4800 & 0.0045 & II\\
52591.2761 & 0.0001 & I\\
52594.3713 & 0.0014 & II\\
\hline
\end{tabular}
\end{center}
\end{table}

\IBVSfig{6cm}{5381-f2.eps}{Unfiltered light curve of GSC 4288-0186.}
%\IBVSfigKey{5381-f2.eps}{GSC 4288-0186}{light curve}

Some of our initial raw data were compromised by moonlight, which
introduced non-linearities into the measurements. As well, the
broad bandwidth of the unfiltered observations can introduce other
non-linearities into the magnitude comparison process, especially
with larger air masses (cf., e.g. Golay, 1974). These facts should
be kept in mind in relation to the apparent out of eclipse
variation.

While a definitive model for the system has not been attempted at
this stage, there exist physically plausible parameters which fit
the data. For light curve modelling we used {\tt ILOT} (Banks, T.
\& Budding, E., 1990). From the spectral class, we assume a temperature 
for the hot star of 8100 K and we have then used standard theoretical
values for the limb darkening, gravity brightening and effective
albedo coefficients given this temperature and effective
wavelength (cf. e.g. Budding, 1993). The wavelength-independent
parameters we found are: the radius, relative to the mean
separation, of the hot star is 0.085~$\pm$~0.007, that of the cool
star is 0.081 $\pm$ 0.006, orbital inclination 88\deg\ $\pm$
0\fdeg5, eccentricity of the orbit 0.075 $\pm$ 0.01 and longitude of
the periastron $\varpi$=25\deg$\ \pm$ 1\deg. The well separated stars make
the mass ratio photometrically indeterminate, so we assumed a
value of 0.78, consistent with the temperature difference for a
Main Sequence model, given the respective luminosities. This well
separated model is then reasonably self-consistent in temperature
difference, mass ratio and ratio of the radii with a A5V+A7V Main
Sequence eclipsing binary system.

This type of modelling has proved effective in locating optimal
eccentricity and orientation parameters for well detached systems
like this. It will be interesting to check for secular variations
of the latter parameter ( $\varpi$ ) in future years.


\references

Banks, T., \& Budding, E., 1990, {\it Astrophys. Space Sci.}, 167,
221

Budding, E., 1993, \emph{An Introduction to Astronomical
Photometry, Cambridge University Press}

Gaspani, A., 1995, 3rd GEOS workshop on variable star data
acquisition and processing techniques, 13-14 May 1995, S.
Pellegrino Terme, Italy

Golay, M., 1974, \emph{Introduction to Astronomical Photometry,
Reidel Pub. Com}

Hroch, F., Nov\'ak, R., 1997, MUNIDOS, {\tt http://munipack.astronomy.cz/}

Kwee, K. K., \& van Woerden, H., 1956, {\it Bull. Astr. Inst.
Neth.}, {\bf 12}, 327

\endreferences

\bigskip
\bigskip
\bigskip

%From IBVS 5616
\IBVSerratum{5381}

Errata for the paper IBVS No. 5381 titled {\it ``GSC 4288-186: a New Eccentric Binary''}:
Minima times reported as

\begin{center}
\begin{tabular}{cc}
52515.4800 & II\\
52591.2761 & I\\
52594.3713 & II\\
\end{tabular}
\end{center}

should be changed as

\begin{center}
\begin{tabular}{cc}
52515.4840 & II\\
52591.2817 & I\\
52594.3767 & II\\
\end{tabular}
\end{center}

\vspace*{2cm}
 
\hfill {\it Volkan Bakis}


\end{document}
