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\begin{document}
\IBVShead{5465}{16 October 2003}

\IBVStitle{The \boldmath{$\gamma$} Doradus Variable HD 19684 -- A Spectroscopic Binary}


\IBVSauth{Kaye, A. B.$^1$; Fekel, F. C.$^{2,3}$}

\IBVSinst{Los Alamos National Laboratory; X-5; MS F-663; Los Alamos, New Mexico 87545, USA; e-mail: kaye@lanl.gov}
\IBVSinst{Center of Excellence in Information Systems; Tennessee State University; 330 10th Avenue North; Nashville, Tennessee  37203, USA; e-mail: fekel@evans.tsuniv.edu}
\IBVSinst{Visiting Astronomer, Kitt Peak National Observatory, National 
Optical Astronomy Observatory, operated by the Association of Universities 
for Research in Astronomy, Inc., under cooperative agreement with the National 
Science Foundation.}

\SIMBADobj{HD 19684}
\IBVStyp{  F1 IV  }
\IBVSkey{spectroscopic binaries}

\begintext

Determining the question of duplicity is crucial for the study of 
$\gamma$ Doradus variables.  These late-A and early-F type stars are a 
recently discovered class of variables defined by Kaye et al. (1999).
Kumar, Ao, \& Quataert (1995) and Willems \&
Aerts (2002) showed that the presence of a close companion produces tidal
effects that can induce pulsation in a star.  Thus, it is important to
determine whether each $\gamma$ Doradus variable is a single star with 
intrinsic pulsation or a close binary with pulsation periods perhaps induced 
by tidal interactions.  As an example of the latter, Handler et al. (2002) 
recently found HD~209295 to be the first star that has light variability 
periods typical of both $\delta$ Scuti and $\gamma$ Doradus variables. 
However, they noted that its $\gamma$ Doradus pulsations are tidally excited.

Recent radial velocities combined with previously-published
data from the literature show that the $\gamma$ Doradus variable HD 19684 
(Henry \& Fekel, 2002) is a spectroscopic binary.

Henry \& Fekel (2002) published a mean radial velocity from three observations.
The individual spectra were obtained with the Kitt Peak National Observatory 
0.9-m coud\'e feed telescope, coud\'e spectrograph, and a 
TI CCD detector.  These spectra are centered at 6430~\AA, have a wavelength 
range of about 80~\AA, and a 2-pixel resolution of 0.21~\AA.  The typical 
signal-to-noise ratio for these spectra ranged from 150 to 250.  The six 
older spectra from Fehrenbach et al.\ (1987), obtained at Haute-Provence
Observatory have a dispersion of 80~\AA~mm$^{-1}$.  

The velocities of Fehrenbach et al.\ (1987) range from 3 to $-$23 km~s$^{-1}$.  
Our three KPNO velocities add to the temporal baseline and range from 0
to 20 km~s$^{-1}$, enabling us to establish that this star is indeed a 
binary and determine a preliminary orbit.

With a total of nine velocities (Table 1) we searched for periods between 1 and 40 days.
The results indicate several possible periods between 31 and 33 days.
With weights of 1.0 and 0.2 for the KPNO and Fehrenbach et al.\ (1987) 
velocities, respectively, orbital solutions were obtained starting with the
four best periods.  An orbit with the eccentricity fixed at zero and a 
period of 31.9456 days resulted in the smallest sum of the squared residuals,
and so we adopt it as the current best preliminary orbit of HD~19684. 
Table 2 lists the orbital elements of this solution and Figure 1 shows 
the velocities compared with the calculated orbit.



\IBVSfig{10cm}{5465-f1.eps}{A phased radial-velocity curve of the primary star comparing
the nine velocities with the computed orbit.  Phase zero is the time of maximum radial 
velocity.} 
%%\IBVSfigKey{5465-f1.eps}{HD 19684}{radial velocity curve}

\begin{table}[!ht]
\caption{Radial Velocities of HD 19684}
\begin{center}
\begin{tabular}{cccc}
\hline
                   &       &  Velocity      & O$-$C   \\
HJD $-$ 2,400,000  & Phase & (km s~$^{-1}$) & (km s$^{-1}$)  \\
\hline
45697.3549 &  0.2211   &     0.0  &    $-$1.3 \\
46001.5229 &  0.7425   &  $-$4.0  &    $-$0.4 \\
46003.5118 &  0.8048   &     3.0  &    $-$1.7 \\
46032.4868 &  0.7118   &  $-$7.0  &       0.7 \\
46060.3410 &  0.5837   & $-$23.0  &    $-$1.8 \\
46321.6451 &  0.7634   &     3.0  &       3.8 \\
52013.605  &  0.9400   &    19.8  &       2.3 \\
52326.620  &  0.7384   &     0.0  &       4.2 \\
52328.610  &  0.8007   &     0.1  &    $-$4.1 \\
\hline
\end{tabular}
\end{center}
\end{table}

\clearpage

\begin{table}[!ht]
\caption{Preliminary Circular Orbital Elements of HD 19684}
\begin{center}
\begin{tabular}{lc}
\hline
Orbital Element &   Value   \\
\hline
Period (fixed) & 31.9456 days\\
Time of maximum velocity &  2,452,015.5 $\pm$ 0.7 days \\
Center of mass velocity  & $-$2.3 $\pm$ 3.1 km s$^{-1}$\\
Semi-amplitude            & 21.8 $\pm$ 3.3  km s$^{-1}$\\
Mass Function & 0.03 $\pm$ 0.02 $M_{\odot}$ \\
$a \sin i$ & 0.06 $\pm$ 0.01 AU\\
$\sigma$ & 4.3  km s$^{-1}$\\
\hline
\end{tabular}
\end{center}
\end{table}



Acknowledgements:

Astronomy at Tennessee State University is supported by NASA grant  
and NCC5-511 as well as NSF grant HRD 97-06268.  This research has made use 
of the SIMBAD database, operated at CDS, Strasbourg, France. This work was supported in a part by the Department of Energy under contract W-7405-ENG-36 with the University of California for operation of Los Alamos National Laboratory.


\references


Fehrenbach, C., Duflot, M., Burnage, R., Mannone, C., Peton, A., \& Genty, V., 
1987, {\it A\&AS}, {\bf 71}, 275

Handler, G., et al., 2002, {\it MNRAS}, {\bf 333}, 262

Henry, G.\ W.\ \& Fekel, F.\ C.,  2002, {\it PASP}, {\bf 114}, 988

Kaye, A. B., Handler, G., Krisciunas, K., Poretti, E., \& Zerbi, F. M., 1999,
{\it PASP}, {\bf 111}, 840

Kumar, P., Ao, C. O., \& Quataert, E. J., 1995, {\it ApJ}, {\bf 449}, 294

Willems, B, \& Aerts, C., 2002, {\it A\&A}, {\bf 384}, 441

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