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\IBVShead{5213}{20 December 2001}

\IBVStitle{ORBITAL ELEMENTS OF SB2 SYSTEM 66 E\lowercase{ri}}


\IBVSauth{YUSHCHENKO, A.V.$^1$;  GOPKA, V.F.$^1$; KHOKHLOVA, V.L.$^2$; TOMKIN, J. $^3$}

\IBVSinst{Astronomical observatory of Odessa National University,
          park Shevchenko, Odessa, 65014, Ukraine, e-mail: yua@lens.tenet.odessa.ua}
\IBVSinst{Institute of Astronomy, Russian Academy of Sciences,
          Pyatnitskaya 48, Moscow, Russia, e-mail: vlk@khokh.msk.ru}
\IBVSinst{Department of astronomy, University of Texas, Austin, TX 78712, USA}

\SIMBADobjAlias{EN Eri}{HD 32964}
\IBVStyp{ CWA }
\IBVSkey{photometry}
\IBVSabs{On the base of 5 high resolution spectra and previously published data}
\IBVSabs{we found a new set of orbital elements of this binary system. All }
\IBVSabs{ elements are in good agreement with previously }
\IBVSabs{published data. Additional observations of the star are necessary to }
\IBVSabs{confirm or reject the light variations of the system and to find the }
\IBVSabs{inclination of the orbit and the rotational periods of components.}

\begintext

The first orbit of 66~Eri (EN~Eri) was published by Frost \& Struve (1924).
They measured hydrogen-core lines and very few other lines.
Young (1976) on the base of 15 radial velocities obtained from 13~\AA/mm spectra
have found a new orbit (P$_{orb}$=5\fday 522731) and pointed that the chemical composition of the
components is different. He used Frost \& Struve (1924) radial velocities
in combination with his own data to improve the determination of period.
He used 24 separate line pairs for radial velocity measurements, including
Fe~II, Ti~II, Ni~II, Si~II, Sr~II, Ca~II, Mg~II lines.

   Schneider (1987) observed 66~Eri in $uvby$ photometric system and reported
finding of weak variability (0\fmm 002 in $v$ and 0\fmm 005 in $u$) with the
period of 7\fday 8586.
In GCVS EN~Eri is designated as a variable star of $\alpha{^2}$~CVn type.
The system has been observed in wide range of wavelengths from X-rays to
far infrared.

Yushchenko et al. (1998) found the effective temperatures and surface gravities
of the components
( T$_{effA}$=11100$\pm$100~K, T$_{effB}=$10900$\pm$100~K, $lg g$=4.2
 for both components)
and found preliminary chemical composition of the components.
Yushchenko et al. (1999) published detailed spectroscopic investigation of
66~Eri based on spectral observations with resolution
 $\Delta\lambda /\lambda$=36000.
They determined chemical composition of the components, and it
appeared that each component was a peculiar star, but each in a different way.
Secondary component showed strong lines of heavy elements, while the
primary one showed only a small overabundance of barium.
Woolf \& Lambert (1999) analyzed Hg abundances in a set of HgMn stars,
using spectra with resolution  $\Delta\lambda /\lambda$=160000-190000.
They included 66~Eri~B in their set of HgMn stars.
66~Eri~A was included for comparison with 66~Eri~B. Woolf \& Lambert (1999)
confirmed the different Hg abundances in the components of 66~Eri:  5.83 for
component B and less than 2.2 for A.

Yushchenko et al (1999) analyzed $HIPPARCOS$ photometry and found light
variation with an amplitude near 0\fmm 005.
They tried to find the period of light variation, it appears that the period
is equal to one half of orbital period and no significant peaks were found
near 7\fday 86.

The phase shift of $HIPPARCOS$ light curve  plotted with the period equal
to one half of the orbital period and two precision radial velocities obtained
from spectra with resolving power 36,000 and S/N$>$100 (see Yushchenko et al.,
1999) permit us to claim that our value of orbital period is more accurate than that given by Young (1976).

In this investigation we used 5 high-dispersion echelle spectra of 66~Eri
obtained at 2.7 meter telescope of McDonald observatory with a spectral
resolution
of 60,000 and S/N ratio $=>$100. We used URAN software (Yushchenko, 1998)
and synthetic spectra of the components calculated by Yushchenko et al. (1999)
for processing the spectra and line identification. Only unblended lines of
Fe~II were used for radial velocity measurements. The technique of
decomposition of a spectrum on Gaussian components was used (Casatella, 1976).
This method permits one to find wavelengths of spectral lines with high
precision.
The obtained radial velocities were averaged with weights inversely
proportional to the width of the spectral order contained a line used.
Results of radial velocity measurements are given in Table 1, where one can
find heliocentric Julian dates of the observations and
exposure times (in seconds),
mean radial velocities (in $km/s$), numbers of used lines and
errors of weighted means (in $km/s$) for each component of the system.
%
\vskip 1cm
%
\centerline{Table 1. Radial velocities}
\vskip 3mm
\begin{center}
\begin{tabular}{ccrccrcc}
\hline
 $HJD_{\odot}$ & Exposure & $V_{r1}$  &  $N$ & $\sigma$ &  $V_{r2}$  &  $N$ & $\sigma$ \\
\hline
 2450689.989 &    120   &    $-$79.5 & 19 & 0.2  &  +139.7 & 19 & 0.3  \\
 2450690.982 &    300   &     $-$4.6 & 17 & 0.2  &   +67.0 & 28 & 0.1  \\
 2450691.990 &    180   &    +96.3 & 22 & 0.3  &   $-$30.5 & 24 & 0.2  \\
 2450692.986 &    240   &   +124.6 & 14 & 0.2  &   $-$59.4 & 28 & 0.2  \\
 2450693.977 &    240   &    +57.7 & 27 & 0.2  &    +5.3 & 25 & 0.2  \\
\hline
\end{tabular}
\end{center}
%
\vskip 1cm

The orbital elements were obtained by a least-squares adjustment to our 5
radial velocities, 2 radial velocities obtained by Yushchenko et al. (1999)
and 15 values from Young (1976), with weights inversely proportional
to squares of their formal errors.
The results and their errors are given in Table 2 together with Young (1976)
results.
%
\vskip 1cm
%
\centerline{Table 2. Orbital elements of 66 Eri}
\vskip 3mm
\begin{center}
%
\begin{tabular}{lrrrr    }
\hline
                      & This work            &                      & Young (1976)& \\
\hline
 $P$, ~~$days$        &  5.522599            &              0.000006& 5.522731   & 0.000009 \\
 $T$, ~~$HJD_{\odot}$  &2441384.11            &                  0.05&2441384.13  & 0.1 \\
 $e$                  &     0.087            &                 0.004& 0.095      & 0.01 \\
 $w$, ~~$^o$          &     160.3            &                   3.4& 161        & 6    \\
 $K_{1}$,  ~$km/s$    &     102.7            &                   0.7& 103.8 & 1.3 \\
 $K_{2}$,  ~$km/s$    &     100.5            &                   0.7& 100.7 & 0.7 \\
 $\gamma$, ~~~$km/s$  &      32.4            &                   0.3& 32.6 & 0.8 \\
 $a_{1}sin~i$, ~$km/s$&~~~$7.77\times 10^{6}$&~~~$0.05\times 10^{6}$&~~~$7.85\times 10^{6}$&~~~$0.1\times 10^{6}$ \\
 $a_{2}sin~i$, ~$km/s$&~~~$7.60\times 10^{6}$&~~~$0.05\times 10^{6}$&~~~$7.61\times 10^{6}$&~~~$0.06\times 10^{6}$ \\
 $M_{1}sin^{3}i$      &     2.35             &                0.03  & 2.38 & 0.05 \\
 $M_{2}sin^{3}i$      &     2.40             &                0.03  & 2.45 & 0.05 \\
 $M_{1}/M_{2}$        &     0.98             &                      & 0.97  & \\
\hline
\end{tabular}
\end{center}
%
\vskip 1cm

The comparison of our results with Young's (1976) solution of the orbit
shows an excellent agreement for all elements.
The errors of our solution are significantly smaller.
Frost \& Struve (1924) data are well fitted by our elements.
Fig. 1 show all available observations of radial velocities of 66 Eri.
Phases were calculated with our elements.

\IBVSfig{8cm}{5213-f1.eps}{Radial velocity curves for 66 Eri. Solid lines are the velocity curves calculated with our new elements. Frost \& Struve's (1924) data are marked by points, Young's (1976) data - by circles, data from Yushchenko et al. (1999) and this work are marked by squares.}

\vskip 1cm

The inclination of the orbit and hence the question of synchronization
of rotation and orbital motion of the components of this binary still
remains doubtful until the light variation found by Yushchenko et al. (1999)
from $HIPPARCOS$ data will be confirmed by more precise photometry and more
reliable estimation of the distance will be available.
%

\vskip 1cm

%

\references

Casatella A., 1976, {\it Astron. Astrophys.}, {\bf 48}, 281
%    \BIBCODE{1976A&A....48..281C}

Frost E.B., Struve O., 1924, {\it Astrophys. J.}, {\bf 60}, 313
%    \BIBCODE{1924ApJ....60..313F}

Schneider H., 1987, {\it Hvar. Observ. Bull.}, {\bf 11}, 29

Woolf V.M.,  Lambert D.L. 1999, {\it Astrophys. J.}, {\bf 521}, 414
%    \BIBCODE{1999ApJ...521..414W}

Young A., 1976, {\it PASP}, {\bf 88}, 275  %  \BIBCODE{1976PASP...88..275Y}

Yushchenko, A.V., 1998, {\it Proc. on the 29th conf. on Variable star Research.
         Brno, Czech Republic}, p. 202  %  \BIBCODE{1998stel.conf..201Y}

Yushchenko, A.V., Gopka, V. F., Khokhlova, V. L., Musaev, F. A., Bikmaev, I. F.
        1998, {\it Contr. Astron. Obs. Skalnate Pleso}, {\bf 27}, 365
     %  \BIBCODE{1998CoSka..27..365Y}

Yushchenko, A.V., Gopka, V. F., Khokhlova, V. L., Musaev, F. A., Bikmaev, I. F.
 1999, {\it Astronomy Letters}, {\bf 25}, 453   % \BIBCODE{1999AstL...25..453Y}

\endreferences

\end{document}
