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[vsnet-preprint 21] CI Cam preprint
CI Cam preprint
Dear Colleagues,
The following paper on CI Cam is accepted for publication as IBVS No. 5081.
The figure is placed at:
http://ftp.kusastro.kyoto-u.ac.jp/pub/vsnet/preprints/CI_Cam/
Regards,
Taichi Kato
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\documentstyle[twoside,epsf]{article}
\input{ibvs2.sty}
\begin{document}
\IBVShead{xxxx}{xx May 2001}
\IBVStitletl{Quiescent Photometry of CI Cam in 1999}
\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{CI Cam}
\IBVStyp{XN}
\IBVSkey{X-ray nova, microquasar, photometry, B[e] star}
\begintext
CI Cam is the optical counterpart of the intense, rapidly fading X-ray
nova XTE J0421+560 in 1998 (Smith et al. 1998; Paciesas and Fishman 1998;
Wagner and Starrfield 1998). An ejection of relativistic jets was observed
(Hjellming and Mioduszewski 1998a, 1998b), which has made CI Cam =
XTE J0421+560 one of the most renowned Galactic microquasars.
Before the giant outburst in 1998, CI Cam had been known as a variable star,
classified as a possible symbiotic star. The variability of this star was
discovered by Miroshnichenko (1994). Miroshnichenko (1994) reported that
spectroscopy of the CI Cam = MWC 84 revealed absorption features typical
for late-type stars. Miroshnichenko (1994) also reported a photometric
period of 11.7 d with an amplitude of 0.3 mag. In order to confirm this
suggested periodicity, we performed CCD photometry.
\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 3723.54,
whose Tycho-2 magnitude is $V=10.50\pm0.04$ and $B-V=+0.79\pm0.07$.
The constancy of comparison star during the run was confirmed by comparison
with GSC 3723.65 and GSC 3723.80.
\IBVSfig{10cm}{fig1.ps}{Light curve of CI Cam. Each point represents nightly
averaged magnitudes.}
\vskip 3mm
A total of 259 useful frames between 1999 October 22 and 1999 December 28
were obtained. The light curve drawn from the resultant data is presented
in Figure 1. The light curve shows relatively irregular variation, with
a total amplitude of 0.2 mag. Small, nightly variations are superimposed
on a general, slowly declining trend. A period analysis has yielded no
coherent periodicity between 1 and 30 d. There was no indication of the
11.7-d periodicity. Post-outburst photometry between 1998 August and
1999 February (Clark et al. 2000) reported small variations, but the
small number of data points made it impossible to analyze the possible
periodicity or the time scale of variations. Clark et al. (2000) suggested
a possible effect of the 1999 event in their post-outburst data. Our
photometry at later epochs than theirs is expected to more closely reflect
the quiescent activity.
\vskip 3mm
The most remarkable short-term variation in our data was observed
on JD 2451485 (1999 November 2), when a 0.10 mag jump was observed within
one day. The brightening lasted less than one day, and the object faded by
0.09 mag on the subsequent night. The time scale of the variation was
comparable to the $e$-folding time of $\sim$0.5 d of the 1999 event.
Since CI Cam was observed to be X-ray active even during quiescence
(cf. Parmar et al. 2000), it is not surprising if a ``miniature"
outburst may have been responsible for the transient optical brightening.
The BATSE earth-occultation light curve
(http://vsnet.batse.msfc.nasa.gov/batse/) does not show a marked increase
of the X-ray flux on the corresponding day, but has a slightly increased
detections 5 to 10 days after the optical brightening. The optical
brightening thus may have been a precursor to the weak X-ray activity.
\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
Clark, J. S., Miroshnichenko, A. S., Larionov, V. M., Lyuty, V. M.,
Hynes, R. I., Pooley, G. G., Coe, M. J., McCollough, M., Dieters, S.,
Efimov, Yu. S., Fabregat, J., Goranskii, V. P., Haswell, C. A.,
Metlova, N. V., Robinson, E. L., Roche, P., Shenavrin, V. I.,
Welsh, W. F., 2000, A\&A, 356, 50
Hjellming, R. M., Mioduszewski, A. J., 1998a, IAUC No. 6857
Hjellming, R. M., Mioduszewski, A. J., 1998a, IAUC No. 6872
Miroshnichenko, A. S., 1994, Odessa Publ., 7, 76
Paciesas, W., Fishman, G., 1998, IAUC No. 6856
Parmar, A. N., Belloni, T., Orlandini, M., Dal Fiume, D., Orr, A.,
Masetti, N., 2000, A\&A, 360, 31L
Smith, D., Remillard, R., Swank, J., Takeshima, T., Smith, E., 1998,
IAUC No. 6855
Wagner, R. M., Starrfield, S. G., 1998, IAUC 6857
\end{document}
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