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\IBVShead{5236}{12 February 2002}

\IBVStitle{New Elements of the contact binary V839 Ophiuchi}

\IBVSauth{Pazhouhesh, R.$^{1}$; Edalati, M.T.$^{2}$}

\IBVSinst{Physics Department, School of Sciences, Ferdowsi University, Mashad, Iran; \\e-mail: rpazhouhesh@science1.um.ac.ir}

\IBVSinst{Physics Department, School of Sciences, Ferdowsi University, Mashad, Iran; \\e-mail: tedalati@science1.um.ac.ir}

\SIMBADobj{V839 Oph}

\begintext

 V839 Oph as a W UMa type contact binary system was first detected
by R. Rigollet in 1947. According to the \textit{General Catalogue
of Variable Stars}\, (GCVS Kholopov~et~al., 1985) the
spectral type of the system is F$8V$ with the period
P=$0\fday40899532$. So far a lot of studies have been conducted on
the period variation and light curve analysis of V839~Oph (see
especially Akalin \& Derman, 1997). The first spectroscopic
observations of this system were done by Rucinski and Lu in 1999.
They found that the mass ratio of the system ($q$=$m_{2}$/$m_{1}$) is
 0.305 with the spectral type of F7V.

The authors made new photoelectric observations of V839 Oph in
2000. The light curves and times of minima resulted from our
observations are given in IBVS (No. 5190, 2001). We used the
latest version of Wilson program (2001) in order to find
simultaneous radial velocity and light curves solutions of the
system.

The $B$, $V$
magnitude differences were converted to intensities and used as a
photometric input data. For radial velocity analysis we used the
29 observations provided by Rucinski \& Lu (1999). The radial
velocity curves along with the two ($B$, $V$) light curves were utilized
simultaneously to determine the geometric and physical elements of
the system.

 For detailed analysis mode 3 of Wilson's (2001) program was used with
constraints for gravity-darkening exponents $g_{1}$=$g_{2}$, the
bolometric albedos $A_{1}$=$A_{2}$, the modified surface
potentials of two components $\Omega_{1}$=$\Omega_{2}$, the limb
darkening coefficients $x_{1}$=$x_{2}$, $y_{1}$=$y_{2}$. We
supposed that there is neither a third light, $l_{3}=0.0$, nor any
spot.

 The parameters of Akalin \& Derman (1997) were taken as a starting
point. We used  the bolometric logarithmic law of limb darkening
for both components and the $x$ and $y$ parameters of the components
were fixed to their theoretical values, as interpolated with VLimp
program by Van Hamme (1993). Since the spectral type of this system
is
 F7V, the temperature of the primary component was assumed to be
$T_{1}$=6550K.
 The following parameters were free to be adjusted: the
orbital inclination $i$; the mass ratio $q$; the temperature of
secondary component $T_{2}$; the potential function $\Omega_{1}$;
the gravity darkening~$g_{1}$; the bolometric albedos $A_{1}$;
the monochromatic luminosity of primary component $L_{1}$; the
semi-major axis ${\it a}$; and the systemic velocity $V_{\gamma}$.
These nine parameters were varied until the solution converged.

\IBVSfig{10cm}{5236-f1.eps}{Open squares show the observed points
and continuous lines show the model fit.}
\IBVSfig{10.2cm}{5236-f2.eps}{The same as Fig.~1 for radial velocity data.}

\vspace*{-0.74cm}

Table~1 summarizes the adopted solution while Table~2 lists the
values of the absolute dimensions of V839 Oph. Similarly Fig.~1 and
Fig.~2 represent the light curves and radial velocity curves,
respectively.

  In a nutshell, the present study of the V839 Oph showed that
 the system posseses partial eclipses and is a A-type contact binary with a degree
of overcontact of $f$ = $(\Omega_{in} - \Omega_{1,2})/(\Omega_{in}
- \Omega_{out}) \cong 23\%$. According to Kopal (1959), the
relation $r_{1} + r_{2}$= 0.75 should be fulfilled for contact
system; therefore, taking the mean values of $r_{1}$ and $r_{2}$,
we have $r_{1} + r_{2} = 0.79$. As a result, V839 Oph is an
overcontact system which has two stars overfilling their
respective Roche lobes.

\begin{table}

\center \caption{The Geometric and Physical elements of the
contact binary system V839 Oph (most quantities are defined in the
text).}

\begin{tabular}{llll}

\hline

Element & Value & \hspace{0.5cm} Element & Value \\

\hline

i & $80.059 \pm 0.378$ & \hspace{0.7cm}  q & $0.305 \pm 0.001$  \\
$a(R_{\odot})$ & $2.982 \pm 0.005$ & \hspace{0.7cm}  $V_{\gamma}(km/s)$ & $-63.76 \pm 0.33$ \\
$x_{1(bol)}$=$x_{2(bol)}$ & 0.641 & \hspace{0.7cm}  $y_{1(bol)}$=$y_{2(bol)}$ & 0.242 \\
$g_{1}=g_{2}$ & $0.630 \pm 0.044$ & \hspace{0.7cm}  $l_{3}$ &  0.00 \\
$\Omega_{1}= \Omega_{2}$ & $2.434 \pm 0.007$ & \hspace{0.7cm}  $A_{1}=A_{2}$ & $0.984 \pm 0.115$ \\
$T_{1}(K)$ & $6650 $ & \hspace{0.7cm}  $T_{2}(K)$ & $6554 \pm 15$ \\
$L_{1B}/(L_{1}+L_{2})$ & $0.756 \pm 0.004$ & \hspace{0.7cm}  $L_{2B}/(L_{1}+L_{2})$ & $0.243 \pm 0.004$ \\
$L_{1V}/(L_{1}+L_{2})$ & $0.753 \pm 0.004$ & \hspace{0.7cm}  $L_{2V}/(L_{1}+L_{2})$ & $0.243 \pm 0.004$ \\
$r_{1(pole)}$ & $0.463 \pm 0.004$ & \hspace{0.7cm}  $r_{2(pole)}$ & $0.271 \pm 0.005$ \\
$r_{1(side)}$ & $0.500 \pm 0.006 $& \hspace{0.7cm}  $r_{2(side)}$ & $0.284 \pm 0.006$ \\
$r_{1(back)}$ & $0.528 \pm 0.088$ & \hspace{0.7cm}  $r_{2(back)}$ & $0.325 \pm 0.012$ \\

\hline

\end{tabular}

\end{table}

\begin{table}

\center \caption{Absolute dimension of V839 Oph calculated for
mean values of Table 1.}

\begin{tabular}{lcc}

\hline  Element & \hspace{2mm} Primary & \hspace{2mm} Secondary  \\

\hline
$Mag_{(bol)}$ & \hspace{2mm} 3.31 & \hspace{2mm} 4.51 \\

$M(M_{\odot})$ & \hspace{2mm} 1.64 & \hspace{2mm} 0.5 \\
$R(R_{\odot})$ & \hspace{2mm} 1.48 & \hspace{2mm} 0.88 \\
$L(L_{\odot})$ & \hspace{2mm} 3.51& \hspace{2mm} 1.14 \\
\hline
\end{tabular}

\end{table}

\references

Akalin, A., and Derman E., 1997, {\it A\&AS}, {\bf 125}, 407.

Kholopov, P.N., 1985, {\it {``General Catalogue of Variable
Stars''}}, {\bf Vol.~II}, Fourth Edition.

Kopal, Z., 1959, Close Binary Systems, Chapman and Hall Ltd.,
London.

Pazhouhesh, R., Edalati, M.T., and Bagheri, M., 2001, {\it IBVS} No. 5190.

Rigollet, A., 1947, {\it l`Astronomie,} {\bf 61}, 54.

Rucinski, S. M., and Lu, W., 1999, {\it AJ}, {\bf 118}, 2451 (paper II).

Van Hamme, W., 1993, {\it AJ}, {\bf 106}, 2096.

Wilson, R. E., 2001 ``The program for eclipsing binary stars''.
Available online  at:
{\tt ftp://ftp.astro.ufl.edu/pub/wilson/lcdcprog/}

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