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[vsnet-preprint 44] UZ Tau preprint
UZ Tau preprint
The following article is accepted for publication as IBVS No. 5121.
The figures are available at:
http://ftp.kusastro.kyoto-u.ac.jp/pub/vsnet/preprints/UZ_Tau/
Regards,
Taichi Kato
===
\documentstyle[twoside,epsf]{article}
\input{ibvs2.sty}
\begin{document}
\IBVShead{xxxx}{xx May 2001}
\IBVStitletl{Photometry of UZ Tau}
\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{UZ Tau}
\IBVStyp{INT}
\IBVSkey{T Tau star, photometry}
\begintext
UZ Tau is a well-known classical T Tau star which is considered to
be surrounded by a circumstellar disk (e.g. Ghez et al. 1994).
The object is also a famous multiple systems, composed of a visual
binary system UZ Tau E and UZ Tau W, both of which are known to be
spectroscopic and speckle binaries, respectively (Jensen et al. 1996;
Mathieu et al. 1996). The object is also considered as a member of
EXORs, or sub-FUORs (Herbig 1989), which show occasional outbursts
lasting $\sim$100 d. More recently, one of EXORs, V1143 Ori, showed
a short-term rise and fall with a time-scale an order of magnitude
shorter than those of the historically known outbursts of EXORs
(Baba et al., in preparation). We selected UZ Tau as one of our
long-term monitoring project of EXORs.
\vskip 3mm
The observations were done on 33 nights between 1996 November 14 and
1997 December 25, 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 20--30 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). UZ Tau is known to be a very close double
(the fainter component has a $B$ magnitude of 15.16, and a spectral
type of M4Ve), but the present photometry was done for the combined light,
since the separation of the components was impossible. The magnitudes
were determined relative to GSC 1833.587 ($V$=13.74), whose constancy
during the run was confirmed using GSC 1833.381 ($V$=13.80).
The magnitudes of comparison and check stars were determined using
HIP 21134 ($V$=9.74, $B-V$=+0.57). Table 1 lists the log of observations,
together with nightly averaged magnitudes.
\begin{table}
\begin{center}
Table 1. Nightly averaged magnitudes of UZ Tau \\
\vspace{10pt}
\begin{tabular}{cccc}
\hline
mid-JD$^a$ & mean mag$^b$ & error$^c$ & N$^d$ \\
\hline
50402.182 & -1.136 & 0.080 & 3 \\
50404.060 & -1.216 & 0.019 & 3 \\
50407.215 & -0.974 & 0.004 & 5 \\
50427.101 & -1.202 & 0.006 & 5 \\
50429.090 & -1.128 & 0.007 & 5 \\
50432.144 & -1.627 & 0.013 & 5 \\
50438.160 & -1.588 & 0.007 & 3 \\
50439.023 & -1.245 & 0.020 & 3 \\
50441.012 & -1.184 & 0.042 & 3 \\
50442.028 & -1.111 & 0.039 & 3 \\
50445.065 & -1.066 & 0.010 & 5 \\
50448.058 & -0.815 & 0.008 & 5 \\
50448.999 & -1.201 & 0.009 & 3 \\
50449.940 & -1.136 & 0.029 & 3 \\
50451.000 & -1.512 & 0.034 & 3 \\
50452.019 & -1.710 & 0.075 & 7 \\
50452.944 & -1.631 & 0.011 & 5 \\
50455.085 & -0.841 & 0.072 & 5 \\
50457.032 & -0.824 & 0.011 & 3 \\
50461.087 & -0.984 & 0.006 & 3 \\
50462.080 & -0.953 & 0.019 & 3 \\
50464.117 & -0.735 & 0.010 & 3 \\
50468.890 & -0.973 & 0.011 & 5 \\
50507.949 & -0.525 & 0.016 & 5 \\
50509.024 & -0.554 & 0.007 & 5 \\
50512.976 & -0.459 & 0.006 & 5 \\
50515.956 & -0.738 & 0.005 & 5 \\
50518.958 & -0.636 & 0.007 & 5 \\
50672.298 & -0.472 & 0.029 & 2 \\
50675.288 & -0.577 & 0.029 & 3 \\
50676.292 & -0.792 & 0.011 & 3 \\
50677.272 & -0.581 & 0.015 & 3 \\
50808.103 & -1.078 & 0.019 & 3 \\
\hline
\end{tabular}
\end{center}
\hskip 45mm $^a$ JD$-$2400000
\hskip 45mm $^b$ Magnitude relative to GSC 1833.587 ($V$=13.74)
\hskip 45mm $^c$ Standard error of nightly average
\hskip 45mm $^d$ Number of frames
\end{table}
\IBVSfig{10cm}{fig1.ps}{Overall light curve of UZ Tau}
\IBVSfig{10cm}{fig2.ps}{Flare (outburst) of UZ Tau}
\vskip 3mm
The light curve is shown in Figure 1. In average, the object was $\sim$0.5
magnitude brighter in 1996 than 1997, which suggest UZ Tau experienced
an active phase in 1996. The most remarkable phenomenon was a flare
peaking on JD 2450432. Figure 2 shows the enlarged light curve of the
flare. The rise of $\sim$0.6 mag took less than two days, and the overall
time scale of the event was $\sim$10 d. Although the amplitude of the
flare ($\sim$1.0 mag) is smaller than those of other small outbursts in
EXORs, the time scale of the event is comparable to the ``rapid" flare
observed in V1143 Ori. The presence of such rapid variation is difficult
to explain by the viscous accretion in the protostellar disk. This may be
another evidence of magnetically controlled accretion supposed in
EXORs stars.
\reference
Ghez, A. M., Emerson, J. P., Graham, J. R., Meixner, M., Skinner, C. J.,
1994, ApJ, 434, 707
Herbig, G. H., 1989, in {\it ESO Workshop on Low Mass Star Formation and
Pre-Main-Sequence Objects}, ed. B. Reipurth
Jensen, E. L. N., Koermer, D. W., Mathieu, R. D., 1996, AJ, 111, 2431
Mathieu, R. D., Martin, E. L., Maguzzu, A., 1996, AAS Meeting 188, 60.05
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
\end{document}
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