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\IBVShead{5358}{20 December 2002}

\IBVStitle{Detection of Short-Period Oscillation in V592 C\lowercase{as}}

\IBVSauth{Kato,~Taichi$^1$; Starkey,~Donn, R.$^2$}

\IBVSinst{Dept. of Astronomy, Kyoto University, Kyoto 606-8502, Japan; e-mail: tkato@kusastro.kyoto-u.ac.jp}

\IBVSinst{AAVSO, 2507 County Road 60, Auburn,, Auburn, Indiana 46706, USA; e-mail: starkey73@mchsi.com}

\SIMBADobj{V592 Cas}
\IBVStyp{ NL }
\IBVSkey{cataclysmic variables, oscillations}


\begintext

   V592 Cas was originally discovered as a blue, luminous object
(LS I +55\deg8) in the northern Milky Way.  Greenstein et al. (1970)
suggested that this object may be a cataclysmic variable (CV), based on
their spectroscopy.  On the blue spectrum by Greenstein et al. (1970)
broad Balmer lines were in absorption, while He~{\sc ii} and
C~{\sc iii}/N~{\sc iii} were in emission, which made UX UMa-type CV
classification likely (Warner 1976).  Africano and Quigley (1978)
obtained high-speed photometry of this object, and concluded that rapid,
non-periodic variations (up to amplitudes of 0.4 mag) were present.
With this finding, the object received a variable star designation of
V592 Cas (Kholopov et al. 1981).  Zwitter and Munari (1994) presented
a CCD spectrum, which showed H$\alpha$ and possibly He~{\sc i} in
emission, confirming the CV nature.  Downes et al. (1995) reported
a temporal variation of the emission lines, particularly in the appearance
of the C~{\sc iii}/N~{\sc iii} lines.

   Huber et al. (1998) obtained time-resolved photometry and spectroscopy,
and obtained an orbital period of $P_{\rm orb}$ = 0.114 d.
Huber et al. (1998) suggested
that V592 Cas appears to be a nova-like CV in the period gap.
Taylor et al. (1998) reported a radial-velocity study and long-term
photometry of this object, and reported a refined orbital period of
0.115063(1) d.  Taylor et al. (1998) also reported the presence of
superhumps with periods of 0.12228(1) and possibly 0.11193(5) d, qualifying
V592 Cas as a permanent superhump system.

   Here we report on the detection of short-term, coherent photometric
oscillations in V592 Cas taken on 2002 October 21.  The observation was
performed with a 36-cm Schmidt--Cassegrain telescope and an unfiltered
SX-10XE camera.  The exposure time was 45 s, and the errors of a single
exposures was estimated to be 0.007 mag.  The zero-point calibration
(approximately on the $R_{\rm c}$ system) was performed using the comparison
stars by Henden and Honeycutt (1995).  The raw data are publicly available
in vsnet-obs 41976 and 41977.\footnote{
{\tt http://www.kusastro.kyoto-u.ac.jp/vsnet/obs41000/msg00976.html} and
{\tt http://www.kusastro.kyoto-u.ac.jp/vsnet/obs41000/msg00977.html}}

   The resultant light curve is shown on Figure 1.  The existence of
short-period recurrent brightenings is apparent.  Such strong short-term
oscillations were not apparent at the time of the observations by
Taylor et al. (1998).

\IBVSfig{10cm}{5358-f1.eps}{Light curve of V592 Cas on 2002 October 21.
Short-period recurrent brightenings were observed.
}

   Figure 2 shows the power spectrum of the light curve.  A strong signal
at a frequency of 66.6(4) d$^{-1}$, corresponding to a period of
0.0150(1) d, is present.  There was no indication of superhumps
close to a period of 0.112--0.122 d as shown by Taylor et al. (1998).

\IBVSfig{10cm}{5358-f2.eps}{Power spectrum of V592 Cas on 2002 October 21.
}

   Figure 3 shows the averaged profile of this 0.0150-d oscillation.
The profile more resembles those of quasi-periodic oscillations (QPOs)
rather a sinusoid.  The variation looked almost coherent within
the length of this observation.

\IBVSfig{10cm}{5358-f3.eps}{Averaged profile of the 0.0150-d oscillation.
}

   From this observation and the available literature, V592 Cas appears
to have two distinct states: (1) state with prominent superhumps and less
prominent short-term variations (cf. Taylor et al. 1998) and (2) state
with prominent short-term, seemingly coherent, variations, almost lacking
superhump-type variations (this study).  It is not yet clear whether
these states correspond to different excitation states observed in
spectroscopy (Downes et al. 1995).  According to Patterson et al. (2002),
short-period high-amplitude QPO-like oscillations in novalike variables
may be a signature of weakly magnetized white dwarf as in intermediate
polars (IPs).  The presently observed ratio of
$P_{\rm oscillation}/P_{\rm orb}$ = 0.13, similar to those of typical
equilibrium spin rates of IPs (cf. King 1993; Wu and Wickramasinghe 1991),
is also suggestive of this interpretation.  If this possibility is
confirmed, V592 Cas may be a unique object in the period gap showing
both properties of permanent superhumps and occasional IP-like, nearly
coherent, photometric oscillations.

\vskip 3mm

This work is partly supported by a grant-in-aid (13640239)
from the Japanese Ministry of Education, Culture, Sports, Science and
Technology.

\newpage

\references

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\endreferences

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