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\IBVShead{0000}{30 June 2009}

\IBVStitletl{Spectroscopy of eclipsing binary HD~65498}{Third component detected}

\IBVSauth{S\c{E}KALSKA, JUSTYNA$^1$; DIMITROV, WOJCIECH$^1$; KRUSZEWSKI, ADRIAN$^1$; PRZYBYSZEWSKA, ANNA$^1$; KURZAWA, KRYSTIAN$^1$; \.ZYWUCKA, NATALIA$^1$; BORCZYK, WOJCIECH$^1$; BARTCZAK, PRZEMYS\L{}AW$^1$; HIRSCH, ROMAN$^1$; FAGAS, MONIKA$^1$; KAMI\'NSKI, KRZYSZTOF$^1$; KWIATKOWSKI, TOMASZ$^1$; SCHWARZENBERG-CZERNY, ALEKSANDER$^{1,2}$; RO\.ZEK, AGATA$^1$}

\IBVSinst{Astronomical Observatory, Adam Mickiewicz University, S\l{}oneczna 36, 60-186 Pozna\'n, Poland}
\IBVSinst{Nicolaus Copernicus Astronomical Center, Bartycka 18, 00-716 Warsaw, Poland}

\SIMBADobj{HD 65498}

\begintext


This paper presents results of spectroscopic observations of HD65498. HD65498 (DY Lynx) is listed in Simbad database as eclipsing binary of Algol type with $V=9\fmm67$ and $(B-V)=0\fmm56$.
Eclipsing nature of HD65498 was detected by SAVS (Semi Automatded Variability Search) (htp://www.astri.uni.torun.pl/~gm/SAVS) (Maciejewski et al., 2003). The light curve is typical for detached binaries and suggests similar components and partial eclipses with amplitude 0.4 mag. Period of HD65498 is 31.5 hour and the ephemeris is:
$Min.I=HJD 2452704.48836 + 1\fday31324 \times E $
$\pm 0.00054\pm 0.00006$.
They observed the star spectroscopically to determine spectral type. Obtained spectrum corresponds to F5V star.
We have observed the object spectroscopically with PST (Poznan Spectroscopic Telescope),
described in Baranowski et al. 2009, which is equipped with 0.5m mirror and fiber-fed echelle spectrograph. The exposure times were 1800s and the spectra cover range from 4500 to 8250 \AA. The thorium argon lamp provides calibration of the spectra with sigma RV of 100m/s. The spectrograph box is thermally stabilized on the level of 0.1 deg.
Data reduction was performed with IRAF echelle package based script. For the RV measurement we have used IRAF FXCOR task. Cross correlation functions reveal three peaks Two of them broad and ... are connected with the eclipsing pair and the central one - the detected third component (the peak is high and narrow). We examined the line profile of the star and its shape is also tripple.

The light curve and radial velocities allow us to obtain Wilson-Devinney model (Wilson 1971) of the system. We treat the third body as a third light. The time span of our spectra is about two months so they are not affected by the light time efect changes.
The eclipsing pair consists of two similar components with masses $1.017 M_{\odot}, 1.048 M_{\odot}$ and radii $1.280R_{\odot}, 1.260 R_{\odot}$, respectively (Table 2).

The components are slightly evolved. Let us try to reconstruct the system using available observations and evolutionary tracks. The color index of the system is $B-V=0.48$ corresponding to temperature of 6450K (F6.5). It's a result of mixing the light of treee components. The masses and radii of the eclipsing pair components corespond to the age of ? Gyr. We applied temperatures to the eclipsing pair from evolutionary tracks.
Using simple equation and basing on the system B-V index we found the color of the third component.
We estimate the masses and radii of the component taking into account this color index and age of the system.

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\centerline{Table 1. Radial velocities measurements}
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\begin{center}
\begin{tabular}{cccc}
\hline
HJD (+2454900) & RV1 (km/s) & RV2 (km/s) & RV3 (km/s)\\
\hline
$12.319274$ & $-103.9$ & 1$45.7$ & $58.0$\\
12.474967 & -54.6 & 91.6 & 58.3\\
12.504987 & -37.2 & 95.7 & 59.3\\
16.330385 & -81.7 & 121.4 & 56.6\\
16.356517 & -70.6 & 111.0 & 57.2\\
16.383448 & -61.0 & 120 & 58.4\\
24.527291 & 91.8 & -14.4 & 55.4\\
24.569706 & 93.1 & -45.8 & 55.6\\
25.413819 & -110.1 & 155.3 & 55.6\\
25.440946 & -114.6 & 157.3 & 55.5\\
35.327167 & 133.0 & -100.7 & 52.3\\
35.353276 & 128.1 & -93.4 & 51.9\\
35.379281 & 117.5 & -79.4 & 52.5\\
\hline
\end{tabular}
\end{center}

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\centerline{Table 2. Preliminary solution for the eclipsing pair.}
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\begin{center}
\begin{tabular}{cccc}
\hline
parameter & component 1 & component 2\\
\hline
$i$ & \multicolumn{2}{c}{$89^{\circ}.2\pm1^{\circ}.5$}\\
$q$ & \multicolumn{2}{c}{$1.03\pm0.13$}\\
$\Omega$ & $6.07\pm0.22$ & $6.27\pm0.62$\\
$l$ & $4.01\pm0.20$ & $3.72\pm0.20$\\
$T(K)$ & $5400$ & $5340\pm10$\\
$M(M_{\odot})$ & $1.017\pm0.050$ & $1.048\pm0.050$\\
$R(R_{\odot})$ & $1.280\pm0.054$ & $1.260\pm0.123$\\
\hline
\end{tabular}
\end{center}

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\IBVSfig{10cm}{LC_en_obr.ps}{Light curve of HD 65498. Compare with the synthetic curve.}

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\IBVSfig{10cm}{RV_en_obr.ps}{Radial velocity curve for the three components of HD65498. The solid line presents RV measurements for the eclipsing pair and the dashed line for the third component.}

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%\centerline{Table 3}
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%\begin{center}
%\begin{tabular}{cccc}
%\hline
%parameter & component 1 & component 2\\
%\hline
%$R_{pole}(R_{\odot})$ & $1.270\pm0.053$ & $1.247\pm0.119$\\
%$R_{point}(R_{\odot})$ & $1.299\pm0.074$ & $1.272\pm0.162$\\
%$R_{side}(R_{\odot})$ & $1.281\pm0.054$ & $1.256\pm0.123$\\
%$R_{back}(R_{\odot})$ & $1.295\pm0.054$ & $1.268\pm0.111$\\
%\hline
%\end{tabular}
%\end{center}

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\references

Maciejewski, G.,Czart, K., Niedzielski, A., Karska, A., 2003, {\it IBVS}, No. 5431

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

Pr\v{s}a, A., Zwitter, T., 2005 {\it ApJ}, {\bf 628}, 426

Baranowski, R., et al., 2009, {\it MNRAS}, {\bf 396}, 2194

\endreferences


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