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\IBVShead{6096}{24 February 2014}

\IBVStitle{Radial velocity solution of the system IP D\lowercase{ra}}


\IBVSauth{KJURKCHIEVA, D.; MARCHEV, D.}

\IBVSinsto{Department of Physics, Shumen University, 9700 Shumen,
Bulgaria}
\IBVSinsto{e-mail: d.kyurkchieva@shu-bg.net, d.marchev@shu-bg.net}


\SIMBADobjAlias{IP Dra}{Hip 99863}

\IBVStyp{ SB1 }

\IBVSkey{spectroscopy}

\IBVSabs{High-resolution spectroscopic observations around the H$_{\alpha}$ line of the star IP Dra covering the whole orbital period are presented.}
\IBVSabs{The first radial velocity solution of the primary corresponded to semiamplitude of $K_{1}\sin i$=65.7 km/s.}


\begintext

The light variability of IP Dra with an amplitude of 0\fmm06
and a period of 1.7184 days was detected by \emph{Hipparcos} (ESA
1997) and the star was classified as EB of $\beta$ Lyr type. The
available data for this star are: $V$=7\fmm76,
$B-V$=0\fmm535, $V-I$=0\fmm61, parallax 8.27 mas (distance
121 pc), spectral type F5, age 2.7 Gyr (ESA 1997; Kazarovets et al. 1999; Nordstr\"om et al. 2004; Malkov et al.
2006).

In order to obtain radial velocity solution of IP Dra we acquired
few tens of spectra with the 2-m telescope of the National
Astronomical Observatory at Rozhen (Table 1). We used a CCD
Photometrics AT200 camera with the SITe SI003AB 1024$\times$1024 pixels chip mounted on the coud\'e spectrograph (grating
B$\&$L632/14.7\deg). The exposure time was 15 min and the mean S/N
ratio was around 60-70.

\vskip 1cm

\centerline{Table 1. Journal of observations.} \vskip 3mm
\begin{center}
\begin{tabular}{cccc}
\hline
Year&Month, date & number of spectra  &Phase range \\
\hline
2004 & Aug 25  & 4           & 0.545-0.685            \\
2005 & Jul 29  & 2           & 0.675                 \\
2006 & Feb 03  & 2           & 0.295                  \\
2006 & Feb 04  & 4           & 0.805-0.825              \\
2006 & Feb 07  & 11          & 0.594-0.755        \\
2006 & Jun 21  & 8           & 0.524-0.60         \\
2006 & Jun 22  & 6           & 0.101-0.186  \\
2006 & Jul 18  & 3           & 0.31, 0.365        \\
2006 & Jul 19  & 14          & 0.792-0.956    \\
2007 & Feb 09  & 1           & 0.175              \\
2007 & Mar 24  & 5           & 0.282-0.322         \\
2007 & Aug 07  & 7           & 0.295-0.435      \\
2007 & Aug 08  & 4           & 0.006-0.030             \\
2007 & Dec 21  & 1           & 0.491                \\
2010 & May 03  & 2           & 0.96                \\
2013 & Aug 25  & 1           & 0.52                \\
\hline
\end{tabular}
\end{center}

\vskip 1cm

Most of the spectra were in the spectral range around the
H$\alpha$ line (6470-6670 ${\rm{\AA}}$) with 0.19
${\rm{\AA}}$/pixel resolution and they covered well the orbital cycle.
Moreover, several spectra around the CaII H $\&$ K and NaD lines
were obtained.

The spectral data were reduced in a standard way using the PCIPS
software packages (Smirnov et al. 1992) by bias subtraction,
flat-field division and wavelength calibration (with Th-Ar
comparison source exposures). $\beta$ Vir was used as a radial
velocity standard.

Our data were phased according to the ephemeris of \emph{Hipparcos} (ESA 1997):
\[{\rm MinI}=2448501.317+1.7184 \times {\rm E}\;.\]  
Normalized H$_\alpha$ spectra around characteristic orbital
phases are shown in Fig.\ 1.

The profiles of the H$\alpha$ line of IP Dra are single-shaped at
all phases and their strength is appropriate to the spectral type
F5 of the primary. The profiles of the CaII H $\&$ K and NaD
lines (Fig.\ 2) also correspond to the F5 primary and do not reveal
contribution of the secondary. These facts allowed us to classify
the target as a single-lined spectroscopic binary with a
low-luminosity secondary.

\IBVSfig{7cm}{6096-f1.eps}{The H$\alpha$ lines of IP Dra
around the eclipses and quadratures.}

\IBVSfig{4cm}{6096-f2.eps}{The spectra of IP Dra around the CaII H $\&$ K lines (left) and NaD line (right) from July 19 2006.}

The FWHM, EW and depth of the H$\alpha$ line change during the
cycle correspondingly in the ranges 3.2-3.9 ${\rm{\AA}}$, 2.1-3
${\rm{\AA}}$ and 0.48-0.63. Their variability do not reveal any
considerable trends with phase.

The Doppler shifts of the H${\alpha}$ line (Fig. 1) confirm that
IP Dra is a binary system. The measured radial velocities were
fitted by a sinusoid with a semi-amplitude $K_{1}\sin
i$=65.7$\pm$1.6 km/s and a systemic velocity $V_{0}$=3.6$\pm$2.1
km/s (Fig.\ 3).

In order to obtain estimations of the fundamental parameters of IP
Dra we made some speculations based on its photometric and
spectral observations.

The small-amplitude quasi-sinusoidal light curve of IP Dra (ESA
1997) implies ellipsoidal variations rather than eclipses because
even grazing eclipses would cause some sharp dips in the light
curve. The absence of spectral features from the secondary means
that its luminosity should be less than 10$\%$ of that of the
primary.

\IBVSfig{5.5cm}{6096-f3.eps}{Radial velocity data of IP Dra and their
fit.}

The solution of the available low-precision, quasi-sinusoidal (\emph{Hipparcos}) light curve is quite ambiguous, i.e.\ it may be reproduced with a great number of combinations of parameters whose values are within large ranges. The number of solutions can be reduced if one assumes that the two components are MS stars and uses the known empirical relations.

Thus the upper limit $L_{2}$=0.1$L_{1}$ allowed us to fix mass ratio
$q$=0.56, secondary temperature $T_{2}$=0.708$T_{1}$=4600 K and relative radius of the secondary $r_{2}$=0.65$r_{1}$. As
a result we obtained solutions within narrow ranges of the fitted
parameters $r_{1}$ (relative radius of the primary) and $i$ (orbital inclination), namely 0.39--0.43 and
50.5--37.5\deg.
For the reasonable low limit $L_{2}$=0.01$L_{1}$ we fixed
$q$=0.316, $T_{2}$=0.5$T_{1}$=3250 K, $r_{2}$=0.422$r_{1}$, and
obtained even narrower ranges of the fitted parameters $r_{1}$ and
$i$: 0.48--0.482 and correspondingly 50--40\deg.

The presented considerations led us to the conclusion that IP Dra
is (or almost is) a semidetached binary with a low-luminosity
secondary component.

The mean rotational broadening of the spectral lines of IP Dra
corresponds to \linebreak $V^{eq}_{1}\sin i$=73 km/s. This means $V^{eq}_{1} \geq $ 95 km/s (equality for $i=50$\deg). If IP Dra is a
synchronized binary (P$_{\rm orb}$=P$_{\rm rot}$) this result leads to an absolute radius $R_{1}\geq $ 3.24 R$_{\odot}$. Thus the primary is
oversized for an F5 MS star. This conclusion from our spectroscopy
supports the big relative radius of the primary derived from the
light curve solution.


\emph{Acknowledgement:} Based on spectral observations collected at the National Astronomical Observatory at Rozhen. The research was supported partly by funds of a project of Scientific Foundation of Shumen University. We are grateful to the anonymous referee, and the editor, L\'aszl\'o Moln\'ar, for the useful notes.

\references

ESA, 1997, {\it The Hipparcos and Tycho Catalogues}, vol. 11, Hipparcos Variability Annex, ESA SP-1200

Kazarovets A. et al., 1999, {\it IBVS}, No 4659

Malkov O., Oblak E., Snegireva E., Torra J., 2006, {\it A\&A},
{\bf 446}, 785

Nordstr\"om, B. et al., 2004, {\it A\&A}, {\bf 418}, 989

Smirnov O., Piskunov N., Afanasyev V., Morozov A., 1992, {\it ASP
Conf.\ Ser.}, {\bf 25}, 344

\endreferences


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