[vsnet-preprint 25] IS Del preprint

[Taichi Kato <tkato>]

IS Del preprint

Dear Colleagues,

   The following article is accepted for publication as IBVS No. 5092.

   The figures are placed under:
   http://ftp.kusastro.kyoto-u.ac.jp/pub/vsnet/preprints/IS_Del/

Regards,
Taichi Kato

===

\documentstyle[twoside,epsf]{article}

\input{ibvs2.sty}

\begin{document}

\IBVShead{xxxx}{xx May 2001}

\IBVStitletl{Outburst Photometry of IS Del}

\IBVSauth{Taichi~Kato$^1$}
\vskip 5mm

\IBVSinst{Dept. of Astronomy, Kyoto University, Kyoto 606-8502, Japan,
          e-mail: tkato@kusastro.kyoto-u.ac.jp}

\IBVSobj{IS Del}
\IBVStyp{UGSS}
\IBVSkey{dwarf nova, photometry}

\begintext

   IS Del (=S 10699) was discovered by Richter (1970).  Kazzenova and
Shugarov (1993) performed extensive photographic observations and
found that this dwarf nova undergoes outbursts very frequently.
The observation by Kazzenova and Shugarov (1993) also showed the
existence of long outbursts.  The above features are in part reminiscent
of an active SU UMa-type dwarf nova, like YZ Cnc.  The author started
CCD photometry in order to test this possibility, and found that
the object entered a long outburst on 1996 September 11.

\vskip 3mm

   The observations were done on seven nights between 1996 September
8 and 18, 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
90--120 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 PSF photometry package developed by the author.
The magnitudes were determined relative to GSC 1632.1157 (Tycho-2 magnitude:
$V=12.04\pm0.29, B-V=+0.29\pm0.28$), whose constancy during the run
was confirmed using two check stars GSC 1632.2126 and GSC 1632.1243.
Barycentric corrections to observed times were applied 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 IS Del \\
\vspace{10pt}
\begin{tabular}{ccccc}
\hline
start$^a$ & end$^a$ & mean mag$^b$ & error$^c$ & N$^d$ \\
\hline
50334.942 & 50334.944 & 6.430 & 0.152 &  3 \\
50337.981 & 50337.982 & 3.821 & 0.037 &  2 \\
50340.986 & 50341.149 & 3.556 & 0.102 & 75 \\
50341.951 & 50342.112 & 3.689 & 0.143 & 85 \\
50343.037 & 50343.058 & 3.593 & 0.142 & 15 \\
50344.095 & 50344.096 & 3.668 & 0.061 &  2 \\
50345.031 & 50345.033 & 4.263 & 0.028 &  2 \\
\hline
\end{tabular}
\end{center}
\hskip 35mm $^a$ BJD$-$2400000

\hskip 35mm $^b$ Magnitude relative to GSC 1632.1157

\hskip 35mm $^c$ Standard error of nightly average

\hskip 35mm $^d$ Number of frames

\end{table}

\IBVSfig{10cm}{fig1.ps}{Light curve of the 1996 September outburst
of IS Del}

\vskip 3mm

   The light curve drawn from these data is presented in Figure 1.
The outburst lasted at least for seven nights, and is comparable in
duration to long outbursts listed in Kazzenova and Shugarov (1993).
The outburst was flat-topped, which is not characteristic of
a superoutburst of an SU UMa-type dwarf nova.  Time-series photometry
on JD 2450341 and 2450342 did not show any hint of periodic modulations
attributable to superhumps (Figure 2).  An analysis using the Phase
Dispersion Minimization (PDM) method (Stellingwerf 1978) did not yield any
significant signal below 0.1 d.  Since the maximum length of each run was
0.16 d, the possibility of a longer period could not be excluded.
All the available observations supports that IS Del is an SS Cyg-type
dwarf nova (UGSS-type in the GCVS classification), with occasional
long outbursts.  The observed amplitude of outburst was 2.9 mag, which
corresponds to the range of 15.6--18.4 $V$, by adopting the Tyhco-2
magnitude for the comparison star.

\IBVSfig{8cm}{fig2.ps}{Enlarged light curve near maximum}

\references

Kazzenova, E. A., Shugarov, S. Yu., 1993, Perem. Zvezdy, 23, 157

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

Richter, G. A., 1970, MVS, 5, 99

Stellingwerf, R. F., 1978, ApJ, 224, 953

\end{document}

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