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[vsnet-preprint 48] TY Psc preprint
Dear Colleagues,
The following article is accepted for publication as IBVS No. 5128.
(Relayed by Kunjaya et al.)
---
\documentstyle[twoside,epsf]{article}
\input{ibvs2.sty}
\begin{document}
\IBVShead{xxxx}{xx May 2001}
\IBVStitle {Superhump in November 2000 Superoutburst of TY Piscium}
\IBVSauth{C.~Kunjaya$^{1,2}$,K.~Kinugasa$^1$,R.~Ishioka$^3$,
T.~Kato$^3$,H.~Iwamatsu$^3$, M.~Uemura$^3$}
\vskip 5mm
\IBVSinst{Gunma Astronomical Observatory, Takayama, Agatsuma, Gunma
377-0702, JAPAN, e-mail: kinugasa@astron.pref.gunma.jp}
\IBVSinst{Dept. of Astronomy, Institut Teknologi Bandung, Ganesa 10,
Bandung 40132, Indonesia, e-mail: kunjaya@as.itb.ac.id}
\IBVSinst{Dept. of Astronomy, Kyoto University, Kyoto 606-8502, Japan,
e-mail: ishioka@kusastro.kyoto-u.ac.jp, tkato@kusastro.kyoto-u.ac.jp,
iwamatsu@kusastro.kyoto-u.ac.jp, uemura@kusastro.kyoto-u.ac.jp}
\IBVSobj{TY Psc}
\IBVStyp{cataclysmic}
\IBVSkey{dwarf novae -- photometry}
\begintext
The SU UMa type dwarf nova TY Psc was found in bright state on 28 Nov
2000 by J. Ripero
(vsnet-campaign 545 :
http://vsnet.kusastro.kyoto-u.ac.jp/vsnet/Mail/vsnet-campaign/msg00545.html
and vsnet-superoutburst 66 :
http://vsnet.kusastro.kyoto-u.ac.jp/vsnet/Mail/vsnet-superoutburst/
msg00066.html). It was then observed photometrically using small
telescopes equipped with V filter, which resembles Johnson V filter and
cooled CCD camera in three sites:
\begin{enumerate}
\item Kyoto University on October 30, 2000, using 25 cm Schmidt Cassegrain,
with ST-7 CCD camera.
\item Ouda Station, Kyoto University, on November 1, 2000, using 60 cm Cassegrain with
PixelVision camera (SITe SI004AB, Cryo Tiger-cooled) and Rc filter.
\item Gunma Astronomical Observatory on November 3, 2000, using 25 cm
Newtonian with
cooled Bitran 11 CCD camera and V filter.
\end{enumerate}
The exposure time was 30 seconds in Kyoto and Ouda, and around 25 to 40
seconds in GAO observation depending on the altitude of the object.
Ouda data was reduced using IRAF APPHOT package. To correct for the read
out noise, the object frames was subtracted by bias frames and for flat
fielding we used twilight frames. GAO and Kyoto data was reduced by
Java$^{TM}$-based aperture photometry package developed by one of the
author (TK). The read out and thermal noise was removed by dark frame
subtraction and flat fielding was done using twilight frames.
Due to unstable weather condition, some of the Kyoto and Ouda data has
to be rejected.
The criterion for the rejection was one of the following condition, (1)
the count of the
comparison star drop to less than 25\% of the average count or (2) the
count is more than
25\% of average count but dropped suddenly more than 25\% of those in
the previous frame.
Figure 1 showed the resulting light curve, the ordinate is the magnitude
of the star
relative to a comparison star. The comparison star used for differential
photometry in
Ouda data is 12.36 mag star GSC 2296.1010, GAO and Kyoto data is a 12.49
mag star GSC 2296.1213.
\IBVSfig{8cm}{fig1.ps}{Light curves of TY Psc obtained at (a) Kyoto, (b)
Ouda, and (c) Gunma.}
The trend of the data from each site was removed using straight-line
fitting.
The three sets of data was then combined to form one data set. Similar
trend removal
procedure was applied once again to the combined data to remove the
influence of observational
environment difference. The final combined and corrected data was then
analyzed using
Phase Dispersion Minimization method (Stellingwerf, 1978), which was
implemented into
PDMWIN 3.0 computer program wrote by Widjaja (1996). The resulting
$\theta$ diagram is
presented in figure 2.
\IBVSfig{8cm}{fig2.ps}{$\theta$ diagram of the period analysis of the
combined data}
>From figure 2 we can estimate the most probable period, that is about
102 minutes.
To get a more precise period determination we took part of the figure 2
that is the valley
around 102 minutes period and fit it to a parabolic curve.
The minimum of the parabola occurs at the trial period 0.0708 day or
101.9 minute.
Using this value we construct the folded light curve and presented in
figure 3.
This graph shows a usual superhump light curve, that is steeper
brightening followed by shallower dimming.
\IBVSfig{8cm}{fig3.ps}{Folded curve of the combined data}
We used full width half maximum of the deepest valley of the $\theta$
diagram as the error
of the period determination. Then the estimated error of the superhump
period found is 0.4 minutes.
In this work we could confirm and refine previous superhump period
estimation of
TY Psc quoted by Szkody and Feinswog (1988). Despite unfavorable
weather in two
observation site, the period determination was relatively accurate. This
is the
consequence of long time covering (4 days) so that slight change in
trial period
will cause significant difference in $\theta$ (see figure 2). Therefore
long time
covering is recommended for accurate determination of superhump period,
provided there
is no phase change between observations. Recalling the 98.4 minutes
orbital period found
by Thorstensen et al. (1996), this superhump period is 3.6\% longer
than the orbital period
which is quite normal for SU UMa type dwarf novae.
\medskip
\begin{references}
Stelingwerf, R.F., 1978, {\it ApJ}, {\bf 224}, 953
Szkody, P., Feinswog L., 1988, {\it ApJ}, {\bf 334}, 422
Thorstensen, J.R., Patterson, J.O., Shambrook A., Thomas, G., 1996, {\it
PASP}, {\bf 108}, 73
Widjaja, A., 1996, http://vsnet.kusastro.kyoto-u.ac.jp/vsnet/
\end{references}
\IBVSefigure{fig1.ps}
\IBVSefigure{fig2.ps}
\IBVSefigure{fig3.ps}
\end{document}
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