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\input ibvs2.sty

\begin{document}
\IBVShead{5627}{24 May 2005}

\IBVStitle{On the orbital period of KQ M\lowercase{on}}

\IBVSauth{Schmidtobreick, L.$^1$; Tappert, C.$^2$; Galli, L.$^3$; Whiting, A.$^4$}

\IBVSinst{European Southern Observatory, Casilla 19001, Santiago 19, Chile}
\IBVSinst{Departamento de Astronom\'{\i}a y Astrof\'{\i}sica, 
          Pontificia Universidad Cat\'olica, Casilla 306, Santiago 22, Chile}
\IBVSinst{Colorado College, 14 East Cache La Poudre St.,
          Colorado Springs, CO 80903 USA.}
\IBVSinst{Cerro Tololo Inter-American Observatory, 
          Casilla 603, La Serena, Chile}

\SIMBADobj{KQ Mon}
\IBVStyp{ UXUMa }
\IBVSkey{stars: spectroscopy - stars: variables: cataclysmic variables}

\IBVSabs{We present time-resolved, medium resolution, optical spectroscopy}
\IBVSabs{of the nova-like variable KQ Mon. The H_alpha emission line }
\IBVSabs{is present in the observed part of the spectrum and shows strong} 
\IBVSabs{orbital variation. Although several aliases remain for the orbital}
\IBVSabs{period, we tentatively determine it as P_orb = 3.08(4) h.}


\begintext

KQ\,Mon was detected as a variable star by Hoffmeister (1943).
It received a first classification as an irregular variable with the 
spectral type
of a carbon star (Cameron \& Nassau 1956), which was changed to
a cataclysmic variable of UX\,UMa subtype by Sion \& Guinan 
(1982) who discussed IUE spectra of this object. 
The latter authors also discuss parallel high speed photometry, which 
showed variation in the form of low amplitude flickering, but no apparent
orbital modulation. 
This classification was later confirmed by Zwitter \& Munari (1994) 
whose optical 
spectrum of KQ\,Mon shows a blue continuum and a strong H$\alpha$ emission line.
Hoard et al. (2002) identified the object in the 2MASS survey and found that 
it is a close visual triple star which was resolved in the 2MASS images.
This might explain the earlier ambiguous spectral classification.

In the framework of the REU (Research Experiences for Undergraduates) 
observation campaign at CTIO (Cerro Tololo Inter-American Observatory)
in February 2004, we performed time-resolved medium resolution
spectroscopy of KQ\,Mon with the aim of obtaining its orbital period.

\begin{table}[b]
\normalsize
\caption{Observational details of the individual spectra.}
\centerline{
\begin{tabular}{c c c c}
\\
\hline
\hline
 \noalign{\smallskip}
\multicolumn{2}{c}{Date \& UT at start of first exposure} & number of exposures & individual exposure time [s]  \\
 \noalign{\smallskip}
\hline
 \noalign{\smallskip}
2004-02-08 & 01:18:38 &  5 & 600 \\
2004-02-08 & 02:17:59 & 41 & 300 \\
2004-02-11 & 00:19:49 & 23 & 300 \\
 \noalign{\smallskip}
\hline
\hline
\end{tabular}}
\end{table}

We observed the object in two nights with the R-C spectrograph at the 
1.5\,m telescope at CTIO, covering about 8.5\,h in total (see Table 1
for details on the observations).
Standard data reduction was performed with IRAF
including bias and flatfield correction and wavelength calibration.
The spectra have a FWHM resolution of 0.26\,nm and a spectral range of
590--710\,nm, thus including the H$\alpha$ 
emission line. No flux calibration has been performed.
All subsequent analysis of the data has been done using MIDAS.

We have averaged the individual spectra, 
for each pixel disregarding the ten values farthest from the median value.
The resulting
average spectrum of KQ\,Mon is plotted in Fig. 1. It mainly shows
a narrow (FWHM = 1.068(2)\,nm) H$\alpha$ emission line with an equivalent width
of -0.46(3)\,nm.
Some absorption features might be due to the secondary star. No low excitation
emission lines are found in the spectrum, thus
confirming the previous classification as UX\,UMa type star.

\IBVSfig{4.7cm}{5627-f1.eps}{The average spectrum of KQ\,Mon.\vspace*{-1cm}}
\IBVSfigKey{5627-f1.eps}{KQ Mon}{spectrum}

\IBVSfig{7cm}{5627-f2.eps}{The radial velocities are plotted against the time of their observation.}
\IBVSfigKey{5627-f2.eps}{KQ Mon}{radial velocity curve}

\vspace*{-0.5cm}

The radial velocities have been determined by fitting a broad
Gaussian to the H$\alpha$ emission line in the individual spectra. 
They have been corrected for
the motion of the observer towards the object. In Fig. 2
the radial velocities are plotted against the heliocentric Julian date.
A clear sinusoidal variation is seen in the data.

We have used the Scargle algorithm (Scargle, 1982) and the 
analysis-of-variance method (Schwarzenberg-Czerny, 1989) 
as implemented in MIDAS, to find the
period in the radial velocities. The resulting periodograms are plotted
in Fig. 3. From these we derive four possible values
for the orbital period at 2.83(4)\,h, 2.95(4)\,h, 3.08(4)\,h, and 3.22(5)\,h,
the most probable alias being the period $P=3.08(4)$\,h.

Using this value for the orbital period and arbitrarily setting the first 
data point (HJD = 2453043.5626) to $\phi = 0$,
we have derived the orbital phase for the time of the observations.
In Fig. 4, the radial velocities are plotted against this orbital
phase. 

\IBVSfig{6cm}{5627-f3.eps}{The periodograms of the radial velocities are 
calculated by Scargle and AOV method, see text for details.}
\IBVSfigKey{5627-f3.eps}{KQ Mon}{periodogram}

\vspace*{-0.4cm}

They were fitted using a minimum of variance method on
the sinusoidal fitting function 
\IBVSeqfig{
\begin{equation}
v(\phi) = \gamma + K_1 \cdot \sin{\left( 2 \pi \left( \phi + 0.5 - \phi_0\right) \right) }
\end{equation}
}{\IBVSalteqfig{5627-e1}}
where $v$ is the measured radial velocity and $\phi$ the orbital phase as
derived above. The fitting parameters are the system velocity $\gamma$, the
semi-amplitude $K_1$ of the radial velocity, and the phase shift $\phi_0$
for the red-to-blue crossing on the velocity curve which in the absence
of discrete
emission sources in the disc corresponds to the inferior
conjunction of the secondary. 

\IBVSfig{7cm}{5627-f4.eps}{The radial velocities are plotted against the orbital phase with respect to the period $P=3.08$\,h, the first data point
being arbitrarily set to phase zero. The best sinusoidal fit is overplotted.}
\IBVSfigKey{5627-f4.eps}{KQ Mon}{radial velocity curve}

\vspace*{-0.4cm}

The stability of the fit has been tested using
Monte-Carlo simulations which also yield the uncertainties of the
individual quantities.
We thus derive the following parameters: $\gamma = 56 \pm 2 $\,km/s, 
$K_1 = 50 \pm 2$\,km/s, and $\phi_0 = 0.111 \pm 0.008$.

An orbital period $P=3.08$\,h would place KQ\,Mon at a position just above the
period gap for cataclysmic variables. Novalike variables in this period bin
tend to be strong candidates for being physical SW\,Sex type stars 
(G\"ansicke, 2005; Rodr{\'{\i}}guez--Gil 2005). We did find some hints for
variable high velocity wings in the individual spectra of KQ\,Mon which would 
confirm this classification, but the
S/N is not sufficient for an unambiguous statement on the presence
of this feature. Furthermore, the presence of absorption features in the
average spectrum might hint towards KQ\,Mon being a magnetic system.

We conclude that further data are needed to a) confirm the present choice of
the orbital period and b) to ascertain a possible magnetic and/or 
SW\,Sex type nature of KQ\,Mon.


\references
Cameron D., Nassau J.J., 1956, {\it  ApJ}, {\bf 124}, 346
%\BIBCODE{1956ApJ...124..346C}

G\"ansicke B.T., 2005, {\it ASP Conf. Ser.}, {\bf 330}, 3, {\it The astrophysics of cataclysmic variables and related objects}

Rodriguez-Gil P.,  2005, {\it ASP Conf. Ser.}, {\bf 330}, 335, {\it The astrophysics of cataclysmic variables and related objects}

Hoard D.W., Wachter S., Clark L.L., Bowers, T.P., 2002, {\it  ApJ}, {\bf 565}, 511
%\BIBCODE{2002ApJ...565..511H}

Hoffmeister C., 1943, {\it  Astron. Nachr.}, {\bf 274}, 36
%\BIBCODE{1943AN....274...36H}

Scargle J.D., 1982, {\it ApJ}, {\bf 263}, 835
%\BIBCODE{1982ApJ...263..835S}

Schwarzenberg-Czerny 1989, {\it MNRAS}, {\bf 241}, 153
%\BIBCODE{1989MNRAS.241..153S}

Sion E.M., Guinan E.F., 1982, in {\it NASA. Advances in Ultraviolet Astronomy}, 460
\ADSBIBCODE{1982auva.nasa..460S}

Zwitter T., Munari U., 1994, A\&AS, {\bf 107}, 503
%\BIBCODE{1994A&AS..107..503Z}

\endreferences

\end{document}

