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\IBVShead{5077}{14 May 2001}

\IBVStitletl{Photometric Periodicity of BZ C\lowercase{am}}{ During the 1999 Fading}

\IBVSauth{Kato, Taichi; Uemura, Makoto}

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

\SIMBADobj{BZ Cam}
\IBVStyp{ NL }
\IBVSkey{cataclysmic variables; VY Scl-type stars}

\begintext

BZ Cam is a well-known cataclysmic variable of novalike (NL) category,
which does not show dwarf nova-type outbursts.  BZ Cam is renowned for
its surrounding bow shock nebula (Krautter et al.\ 1987; Hollis et al.\ 1992),
and highly variable appearance of P Cyg profiles in its spectra (originally
discovered by J. R. Thorstensen and presented in Patterson et al.\ 1996;
Ringwald and Naylor 1998).  BZ Cam has been playing an important role in
understanding the formation of high-speed winds from cataclysmic variables.
The binary nature of BZ Cam was studied by Lu and Hutchings (1985) and
Patterson et al.\ (1996).  The best determined orbital period is
0\fday153693(7).

Another noteworthy characteristic of BZ Cam is its occasional fadings,
which makes BZ Cam as one of VY Scl-type novalike variables.  The first
historical fading was discovered on Harvard Plates by Garnavich and
Szkody (1988).  The second ever-observed fading was in 1999 (Watanabe
2000, 2001).  We performed CCD observations during this fading.

The CCD observations were done using an unfiltered ST-7 camera attached
to the Meade 25-cm Schmidt--Cassegrain telescope.  The exposure time
was 30 s.  The images were dark-subtracted, flat-fielded, and analyzed
using the Java$^{\rm TM}$-based aperture photometry package developed
by one of the authors (TK)\@.  The magnitudes were determined relative
to GSC 4362.125 ($V=12.87$, $B-V=+0.78$) which constancy was confirmed
using GSC 4362.861 ($V=14.00$, $B-V=+0.67$).  The magnitudes of the
comparison and check stars are taken from Henden and Honeycutt (1995).
A total of 957 observations between 1999 October 3 and 1991 December 8
were obtained.  Our observations were done at the bottom of the
fading.  Barycentric corrections were applied to the observed times
before the following analysis.

The resultant light curve is shown in Figure 1.  The object showed
short-term variations but little long-term variation, which is consistent
with that the observations were done at the bottom of the fading.
The period analysis using the Phase Dispersion Minimization (PDM) method
(Stellingwerf 1978) has revealed a clear (more than 5-sigma) periodicity
close to the reported orbital period (Figure 2).  The strongest period
is 0\fday15634(1), which is 1.7\% longer than the orbital period.
The averaged amplitude at the orbital period is less than 0\fmm03, which
excludes the orbital period as the origin of variations.

\IBVSfig{10cm}{5077-f1.ps}{Light curve of BZ Cam}

\IBVSfig{10cm}{5077-f2.ps}{Periodogram of BZ Cam}

\clearpage

\IBVSfig{10cm}{5077-f3.ps}{Phase-averaged light curve at $P=0\fday15634$}

The detection of a strong period slightly longer than the orbital
period strongly suggests the presence of superhumps.  Observations in
the high state by Patterson et al.\ (1996) also suggested the presence of
signals close to, but slightly different from the orbital period, but
the amplitude of present observation (slightly larger than 0\fmm2)
is much larger than those (0\fmm03) suspected by Patterson et al.\ (1996).
The profile of the light curve (Figure~3) is also characteristic
to those of usual superhumps, but has a shoulder on the fading branch,
which is reminiscent of some of low-amplitude superhump candidates
reported by Patterson et al.\ (1996).  Our observation suggests that
superhumps in BZ Cam is enhanced during its low state ({\it transient\/}
permanent superhumps?), phenomenologically contrary to SU UMa-type dwarf
novae, which usually show superhumps during superoutbursts.
The fractional superhump excess of 1.7\% is relatively small for objects
of this orbital period (e.g.\ Patterson 1999).  Different excitation
mechanisms may be responsible for superhumps in BZ Cam, from other novalike
systems with permanent superhumps.

\bigskip

Part of this work is supported by a Research Fellowship of the
Japan Society for the Promotion of Science for Young Scientists (MU).

\references

Garnavich, P., Szkody, P., 1988, {\it PASP}, {\bf 100}, 1522

Henden, A. A., Honeycutt, R. K., 1995, {\it PASP}, {\bf 107}, 324

Hollis, J. M., Oliversen, R. J., Wagner, R. M., Feibelman, W. A.,
1992, {\it ApJ}, {\bf 393}, 217

Krautter, J., Radons, G., Klaas, U., 1987, {\it A\&A}, {\bf 181}, 373

Lu, W., Hutchings, J. B., 1985, {\it PASP}, {\bf 97}, 990

Patterson, J., 1999, in: Disk Instability in Close Binary Systems,
eds.\ S. Mineshige and J. C. Wheeler (Universal Academy Press, Tokyo),
p.\ 61

Patterson, J., Patino, R., Thorstensen, J. R., Harvey, D., Skillman, D. R.,
Ringwald, F. A., 1996, {\it AJ}, {\bf 111}, 2422

Ringwald, F. A., Naylor, T., 1998, {\it AJ}, {\bf 115}, 286

Stellingwerf, R. F., 1978, {\it ApJ}, {\bf 224}, 953

Watanabe, T., 2000, {\it VSOLJ Variable Star Bull.}, {\bf 37}, 1

Watanabe, T., 2001, {\it VSOLJ Variable Star Bull.}, {\bf 38}, 1

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