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[vsnet-preprint 33] FX Cep preprint
Dear Colleagues,
The following article on FX Cep is accepted for publication as IBVS 5103.
The figures are available at:
http://ftp.kusastro.kyoto-u.ac.jp/vsnet/preprints/FX_Cep/
Regards,
Taichi Kato
===
\documentstyle[twoside,epsf]{article}
\input{ibvs2.sty}
\begin{document}
\IBVShead{xxxx}{xx May 2001}
\IBVStitletl{Outburst Photometry of FX Cep}
\IBVSauth{Taichi~Kato$^1$, Daisaku~Nogami$^{2,1}$, Hajime~Baba$^{3,1}$}
\vskip 5mm
\IBVSinst{Dept. of Astronomy, Kyoto University, Kyoto 606-8502, Japan,
e-mail: tkato@kusastro.kyoto-u.ac.jp}
\IBVSinst{Hida Observatory, Kyoto University, Gifu 506-1314, Japan,
e-mail: nogami@kwasan.kyoto-u.ac.jp}
\IBVSinst{Astronomical Data Analysis Center, National Astronomical
Observatory, Mitaka, Tokyo 181-8588, Japan,
e-mail: hajime.baba@nao.ac.jp}
\IBVSobj{FX Cep}
\IBVStyp{UGSS}
\IBVSkey{dwarf nova, photometry}
\begintext
FX Cep (= GR 95) was discovered by Rosino (1962) as a dwarf nova.
Rosino (1962) reported frequent outburst, with the shortest interval
between them being 11 d, and the presence of a long outburst.
The pattern of outburst is thus somewhat reminiscent of a active
SU UMa-type dwarf nova. The detection of an outburst was announced
by T. Vanmunster (1995). We started time-resolved CCD photometry
in order to search for possible superhumps.
\vskip 3mm
The outburst observations were done between 1995 July 31 and August 5,
using a CCD camera (Thomson TH~7882, 576 $\times$ 384 pixels,
on-chip 2 $\times$ 2 binning adopted) attached to the Cassegrain focus of
the 60 cm reflector (focal length=4.8 m) at Ouda Station, Kyoto University
(Ohtani et al. 1992). An interference filter was used which had been
designed to reproduce the Johnson {\it V} band. The exposure time was
60--90 s, depending on the transparency. The frames were first corrected
for standard de-biasing and flat fielding, and were then processed by a
microcomputer-based aperture photometry package developed by one of the
authors (TK). A total of 134 useful frames were obtained during this
outburst. In addition to this, we observed this star in quiescence in two
occasions on 1990 August 10 and 1995 February 27. The magnitudes were
determined relative to GSC 4259.2106 (GSC magnitude 12.00), whose constancy
during the run was confirmed using GSC 4259.690 (GSC magnitude 11.64).
Barycentric corrections were applied to the observed times before the
following analysis. Table 1 lists the log of observations, together with
nightly averaged magnitudes.
\begin{table}
\begin{center}
Table 1. Nightly averaged magnitudes of FX Cep \\
\vspace{10pt}
\begin{tabular}{ccccc}
\hline
start$^a$ & end$^a$ & mean mag$^b$ & error$^c$ & N$^d$ \\
\hline
48114.167 & 48114.168 & 6.82 & 0.73 & 2 \\
49776.329 & 49776.329 & 6.71 & - & 1 \\
49930.124 & 49930.243 & 2.790 & 0.003 & 100 \\
49931.279 & 49931.284 & 2.571 & 0.111 & 5 \\
49932.281 & 49932.292 & 2.745 & 0.046 & 13 \\
49933.309 & 49933.312 & 2.779 & 0.114 & 6 \\
49934.307 & 49934.312 & 2.749 & 0.070 & 6 \\
49935.305 & 49935.309 & 3.148 & 0.092 & 4 \\
\hline
\end{tabular}
\end{center}
\hskip 35mm $^a$ BJD$-$2400000
\hskip 35mm $^b$ Magnitude relative to GSC 4259.2106
\hskip 35mm $^c$ Standard error of nightly average
\hskip 35mm $^d$ Number of frames
\end{table}
\IBVSfig{10cm}{fig1.ps}{Light curve of the 1995 July-August outburst
of FX Cep. Nightly averaged magnitudes and errors are given except
for the first night.}
\vskip 3mm
The 1995 July-August outburst lasted at least six days, which is
comparable to the long outburst reported by Rosino (1962). The outburst
rose and faded slowly, and did not resemble a superoutburst of
an SU UMa-type star, which has a linear plateau portion. Figure 2
depicts the detailed light curve obtained on 1995 July 31. A 3.8 hour
continuous run did not reveal any hint of superhumps. This object is
thus classified as an SS Cyg-type dwarf nova (UGSS type in GCVS).
The object was spectroscopically observed by Liu et al. (1998).
They reported the detection of features of the secondary, which implies
that FX Cep is a relatively long-period system. This finding is
consistent with our classification as an SS Cyg-type star.
\IBVSfig{10cm}{fig2.ps}{Enlarged light curve on the 1995 July 31}
\vskip 3mm
The average of three frames taken in quiescence has yielded an averaged
magnitude (relative to GSC 4259.2106) of 6.78$\pm$0.50. The total amplitude
of the outburst is thus 4.2$\pm$0.5 mag. This value is remarkably larger
than was originally reported (2.5 mag), which may have been due to the
confusion with the close companion by Rosino (1962). The correct
identification is given in Downes et al. (1997).
\references
Downes, R., Webbink, R. F., Shara, M. M., 1997, PASP, 109, 345
Liu, Wu, Hu, J. Y., Zhu, X. H., Li, Z. Y., 1998, ApJS, 122, 243
Ohtani, H., Uesugi, A., Tomita, Y., Yoshida,
M., Kosugi, G., Noumaru, J., Araya, S., Ohta, K.
1992, Memoirs of the Faculty of Science, Kyoto University,
Series A of Physics, Astrophysics, Geophysics and Chemistry,
38, 167
Rosino, L., 1962, Asiago Contr. No. 132
Vanmunster, T., 1995, Cataclysmic Variables Circular, No. 49
\end{document}
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