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BZ Cam paper
Dear Colleagues,
The following article is accepted for publication as IBVS No. 5078.
The figures are placed at:
http://ftp.kusastro.kyoto-u.ac.jp/pub/vsnet/preprints/BZ_Cam/
Regards,
Taichi Kato
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\documentstyle[twoside,epsf]{article}
\input{ibvs2.sty}
\begin{document}
\IBVShead{xxxx}{xx May 2001}
\IBVStitletl{Photometric Periodicity of BZ Cam during the 1999 Fading}
\IBVSauth{Taichi~Kato$^1$, Makoto~Uemura$^1$}
\vskip 5mm
\IBVSinst{Dept. of Astronomy, Kyoto University, Kyoto 606-8502, Japan,
e-mail: tkato@kusastro.kyoto-u.ac.jp,\\
uemura@kusastro.kyoto-u.ac.jp}
\IBVSobj{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
0.153693(7) d.
\vskip 3mm
Another noteworthy characteristics 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 observed in 1999
(Watanabe 2000, 2001). We performed CCD observations during this fading.
\vskip 3mm
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 ($V=12.87, B-V=+0.78$) whose 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.
\IBVSfig{10cm}{fig1.ps}{Overall light curve of BZ Cam}
\vskip 3mm
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 0.15634(1) d, which is 1.7\% longer than the orbital period.
The averaged amplitude at the orbital period is less than 0.03 mag, which
excludes the orbital period as the origin of variations.
\IBVSfig{8cm}{fig2.ps}{Period analysis of BZ Cam}
\vskip 3mm
\IBVSfig{8cm}{fig3.ps}{Phase-averaged light curve at P=0.15634 d}
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 0.2 mag)
is much larger than those (0.03 mag) 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.
\vskip 3mm
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, PASP, 100, 1522
Henden, A. A., Honeycutt, R. K., 1995, PASP, 107, 324
Hollis, J. M., Oliversen, R. J., Wagner, R. M., Feibelman, W. A.,
1992, ApJ, 393, 217
Krautter, J., Radons, G., Klaas, U., 1987, A\&A, 181, 373
Lu, W., Hutchings, J. B., 1985, PASP, 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, AJ, 111, 2422
Ringwald, F. A., Naylor, T., 1998, AJ, 115, 286
Stellingwerf, R. F., 1978, ApJ, 224, 953
Watanabe, T., 2000, {\it VSOLJ Variable Star Bull.}, 37, 1
Watanabe, T., 2001, {\it VSOLJ Variable Star Bull.}, 38, 1
\end{document}
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