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\IBVShead{5775}{31 May 2007}

\IBVStitletl{The Ultra-Compact Binary Candidate}{ KUV~23182+1007 is a Bright Quasar}

\IBVSauth{Southworth, J.$^1$; Schwope, A.$^2$; G\"ansicke, B. T.;$^1$ Schreiber, M.$^3$}

\IBVSinst{Department of Physics, University of Warwick, Coventry, CV4 7AL, UK, 
email: j.k.taylor@warwick.ac.uk, Boris.Gaensicke@warwick.ac.uk}

\IBVSinst{Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany}

\IBVSinst{Departamento de Fisica y Astronomia, Universidad de Valparaiso, Avenida Gran Bretana
1111, Valparaiso, Chile}

\SIMBADobjAlias{KUV 23182+1007}{[DWS97] Peg 5}
\SIMBADobjAlias{KUV 23061+1229}{WD 2306+122}
\NEDobj{KUV 23182+1007}
\GCVSobj{ES Cet}
\IBVStyp{ CWA }
\IBVSkey{spectroscopy}

\IBVSabs{KUV 23182+1007 was identified as a blue object in the}
\IBVSabs{Kiso UV Survey in the 1980s. Classification-dispersion}
\IBVSabs{spectroscopy showed a featureless continuum except for}
\IBVSabs{a strong emission line in the region of He II 4686 A. This is}
\IBVSabs{a hallmark of the rare AM CVn class of cataclysmic variable}
\IBVSabs{star, so we have obtained a high-S/N blue spectrum of this}
\IBVSabs{object to check its classification. Instead, the spectrum}
\IBVSabs{shows a strong quasar-like emission line centred on 4662 A.}
\IBVSabs{Comparison with the SDSS quasar template spectra confirms that}
\IBVSabs{KUV 23182+1007 is a quasar with a redshift of z = 0.665.}

\begintext

The Kiso Ultraviolet Survey (Noguchi et al., 1980; Kondo et al., 1984)  identified 1186
objects with blue colours in a set of fields observed using the 1.0-m Schmidt telescope of
Kiso Observatory. Classification-dispersion spectroscopy of these objects were presented in a
series of papers by Wegner and colleagues. The spectra of three objects, KUV~01584$-$0939,
KUV~23182+1007 KUV~23061+1229, were given by Wegner et al.\ (1987) and Wegner \&
McMahan (1988). All three of these showed an interesting strong emission in the region of the
He~II 4686~\AA\ spectral line.

However, confusion arose between the objects KUV~23182+1007 and KUV~23061+1229 in Wegner \&
McMahan (1988). In that work, both objects were found to have He~II 4686~\AA\ emission lines
(with some night-to-night variability noted), but the names in the figure titles and figure
captions were in mutual disagreement. Koester et al.\ (2001) have since found that
KUV~23061+1229 is a white dwarf of type DA.

Strong He~II emission is a characteristic of the rare AM~CVn class of cataclysmic variable
stars (Warner, 1995; Southworth et al., 2006). These objects are particularly interesting
ultra-short period helium-rich systems which are thought to be interacting binaries composed
of two degenerate objects, the mass donor being a helium white dwarf. KUV~01584$-$0939 has
since been confirmed to be an AM~CVn star (Warner \& Woudt, 2002; Espaillat et al., 2005),
and is included in the {\em General Catalogue of Variable Stars} under the name ES~Ceti.

As very few AM~CVn systems are known we have obtained a spectrum of the second of the
objects, KUV~23182+1007, in order to investigate its classification as a cataclysmic
variable. We also obtained a spectrum of KUV~23061+1229 in order to confirm that it is a
white dwarf and to fully clear up the confusion over the identities of these two objects. For
these observations we adopted the object identifications and sky co-ordinates as given by the
CDS {\it Simbad} tool\footnote{\tt http://simbad.u-strasbg.fr/simbad/sim-fid}.

Two consecutive long-slit spectra of KUV~23182+1007, immediately followed by one spectrum of
KUV~23061+1229, were obtained on the night of 2007 May 19. We used the LDSS3 spectrograph
attached to the 6.5-m Magellan Clay telescope at Las Campanas Observatory, Chile. The
VPH\_Blue grism was used along with a slit width of 0.75\arcs, giving a useful
wavelength coverage of 4000--6130~\AA\ (depending on brightness) at a reciprocal dispersion
of 0.68~\AA/pixel. From the arc lamp and sky lines we estimate a resolution of
approximately 2~\AA. Wavelength and flat-field calibration was achieved using observations of
helium/neon/argon and quartz lamps, taken immediately after the science spectra and at the
same sky position. The two science spectra of KUV~23182+1007 have been combined and rebinned
to increase the signal-to-noise ratio, resulting in a single spectrum with a reciprocal
dispersion of 2~\AA/pixel. The effective midpoint of this observation is HJD
2~454~240.88628. The midpoint of the spectrum of KUV~23061+1229 occurred at HJD
2~454~240.90236.

\IBVSfig{10cm}{5775-f1.eps}{Magellan/LDSS3 spectrum of the second AM~CVn candidate,
KUV~23061+1229, confirming that this object is a DA white dwarf}
 \IBVSfigKey{5775-f1.eps}{KUV 23061+1229}{spectrum}

The spectrum of KUV~23061+1229 (Fig.~1) is clearly that of a DA white dwarf, in agreement
with the results of Koester et al.\ (2001) and its inclusion in the white dwarf catalogue of
McCook \& Sion (1999). We have therefore adopted the atmospheric parameters found by Koester
et al.\ (2001) to calculate a model spectrum (G\"ansicke et al., 1995)  of KUV~23061+1229 and
used this to divide out the wavelength-dependent response function of the spectrograph from
the spectrum of KUV~23182+1007.

The KUV~23182+1007 spectrum is plotted in Fig.~2 and shows a strong emission line at
4660~\AA\ which we identify to be the Mg 2800~\AA\ line which is a characteristic feature of
quasar spectra. In Fig.~2 we have also plotted a template quasar spectrum\footnote{The
spectrum was obtained from {\tt
http://www.sdss.org/dr5/algorithms/spectemplates/spDR2-029.fit}} from the {\it Sloan Digital
Sky Survey} to which we have applied a redshift of $z = 0.665$. It can be seen that several
additional quasar emission lines match the spectrum of KUV~23182+1007, confirming that this
object is a bright ($B = 16.8$) quasar with a redshift of $z = 0.665$.

As active galactic nuclei are often X-ray sources we have investigated the XMM-Newton and
ROSAT databases for sources at the position of KUV~23182+1007. This region of sky has not
been observed using pointed observations by these satellites. However, the ROSAT All-Sky
Survey\footnote{The ROSAT All-Sky Survey catalogue can be accessed using the CDS {\it VizieR}
service at {\tt http://cdsweb.u-strasbg.fr/viz-bin/VizieR-2?-source=IX/29}} (Voges et al.,
1999, 2000) includes an exposure of 444~s of this position, in which a source
RXS~J232044.6+102354 is detected with a count rate of $0.0249 \pm 0.0094$~counts~s$^{-1}$.
This is within 6\arcs\ of the position of KUV~23182+1007, and over 35\arcm\
from the next nearest X-ray source. Given the quoted ROSAT positional error of
15\farcs, this is a strong detection. The detected X-ray emission is consistent
with our identification of KUV~23182+1007 as a quasar.

\IBVSfig{10cm}{5775-f2.eps}{Magellan/LDSS3 spectrum of the main AM~CVn candidate,
KUV~23182+1007 (upper solid line), after combining and rebinning. A template quasar spectrum
from the SDSS is also shown (lower solid line) after applying a redshift of $z = 0.665$ to the
wavelength scale. The stronger quasar emission lines are labelled with their rest wavelengths,
taken from Vanden Berk et al.\ (2001)}
 \IBVSfigKey{5775-f2.eps}{KUV 23182+1007}{spectrum}

We have therefore clearly identified that KUV~23182+1007 is an X-ray emitting quasar with a
redshift of $z = 0.665$, and confirmed that KUV~23061+1229 is a normal DA white dwarf. The
classification of KUV~23182+1007 in {\it Simbad} and catalogues of cataclysmic variables
(Downes et al., 2001; Ritter \& Kolb, 2003) should be corrected. This report is intended to
avoid other researchers using valuable telescope time to investigate the basic properties of
KUV~23182+1007.

\newpage

\IBVSedata{5775-t1.txt}
\IBVSdataKey{5775-t1.txt}{KUV 23061+1229}{spectrum}
\IBVSedata{5775-t2.txt}
\IBVSdataKey{5775-t2.txt}{KUV 23182+1007}{spectrum}

\references

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Koester, D., et al., 2001, {\it A\&A}, {\bf 378}, 556

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McCook, G.P., Sion, E.M., 1999, {\it ApJS}, {\bf 121}, 1

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