\documentstyle[twoside,epsf]{article}

\input{ibvs2.sty}

\begin{document}

\IBVShead{5097}{30 May 2001}

\IBVStitle{Outburst Photometry of T\lowercase{mz}V36}

\IBVSauth{Kato, Taichi; Uemura, Makoto}

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

\IBVSobj{TmzV36}
\IBVStyp{ UG }
\IBVSkey{dwarf nova, photometry}

\begintext

TmzV36 is a variable star discovered by Takamizawa (1998).
The J2000.0 coordinates are 09\hr16\mm50\fsec7, +28\deg 49\arcm 42\arcs.
Takamizawa (1998) reported only two positive detections on 1994 November
29--30. He also reported that the star is visible at mag 18 on DSS 1.
Since Takamizawa's record suggested an outburst of a dwarf nova-type
variable, the object has been monitored since 1998 by VSNET
(http://www.kusastro.kyoto-u.ac.jp/vsnet/) members. No further outburst
had been reported until Schmeer's detection on 1999 November 17.528 UT,
at unfiltered CCD magnitude of 14.7 (Schmeer 1999). The rapid rise
reported by Schmeer (1999), together with the subsequent evolution of
the event, confirmed the suggested dwarf nova-type classification.
The lack of further outbursts until 2001 April supports the low frequency
of outbursts in TmzV36. We started time-resolved CCD photometry upon
this alert, only 1\fday3 after Schmeer's detection.

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.
A total of 621 useful frames were obtained. The images were dark-subtracted,
flat-fielded, and analyzed using the Java$^{\rm TM}$-based PSF photometry
package developed by one of the authors (TK)\@. The flux of the object was
determined relative to GSC 1957.358 (GSC magnitude 12.65), whose constancy
during the run was confirmed by comparison with anonymous fainter
stars. Barycentric corrections to the observed times were applied
before the following analysis. The log of observations together with
nightly average magnitudes is given in Table 1. The light curve drawn
from these data is presented in Figure 1.

As seen in Figure 1 and Table 1, TmzV36 rapidly faded following the
outburst maximum. The maximum rate of decline was 1.0 mag\,d$^{-1}$,
which is comparable to those of normal outbursts of SU UMa-type dwarf
novae. However, some of short-period SS Cyg-type dwarf novae also show
similar rapid declines. The exact classification of the dwarf nova
subtype awaits further observations. The object returned to quiescence
within 7 days of the outburst detection. The measured amplitude of the
outburst from this observation was 3\fmm0. Since Takamizawa's
detection in 1994 was 1\mm\ brighter than the present outburst, there
may be two types of outbursts, possibly suggesting the SU UMa-type
nature. Figure 2 shows the enlarged light curve of the first three
nights of the outburst. Only rapid fading was observed, and no
definitely periodic modulations attributable to superhumps were
detected.

\newpage

\begin{table}
\caption{Nightly averaged magnitudes of TmzV36}
\begin{center}
\begin{tabular}{ccccr}
\hline
start$^a$ & end$^a$ & mean mag$^b$ & error$^c$ & $N^d$ \\
\hline
51501.341 & 51501.349 & 2.970 & 0.044 & 12 \\
51502.141 & 51502.245 & 3.519 & 0.020 & 201 \\
51503.173 & 51503.340 & 4.512 & 0.029 & 264 \\
51504.108 & 51504.150 & 5.480 & 0.318 & 80 \\
51508.349 & 51508.365 & 6.258 & 0.946 & 23 \\
51509.358 & 51509.370 & 5.881 & 0.264 & 17 \\
51512.227 & 51512.230 & 5.780 & 0.492 & 10 \\
51513.222 & 51513.225 & 5.866 & 0.984 & 8 \\
51516.333 & 51516.337 & 6.425 & 0.949 & 6 \\
\hline
\end{tabular}

\normalsize
\begin{tabular}{l@{ }l}
$^a$ & BJD${}-{}$2400000 \\
$^b$ & Magnitude relative to GSC 1957.358 \\
$^c$ & Standard error of nightly average \\
$^d$ & Number of frames \\
\end{tabular}
\end{center}
\end{table}

\IBVSfig{10cm}{5097-f1.ps}{Light curve of TmzV36}

\clearpage

\IBVSfig{10cm}{5097-f2.ps}{Enlarged light curve of TmzV36. Each point
represents averages and errors of 0.004-d bins}

The authors are grateful to VSNET members for providing visual
observations covering years, and P. Schmeer for promptly and publicly
notifying the outburst. Part of this work is supported by a Research
Fellowship of the Japan Society for the Promotion of Science for Young
Scientists (MU).

\references

Schmeer, P., 1999, {\it VSNET alert circulation}, No.\ 3718 (available from \\
http://www.kusastro.kyoto-u.ac.jp/vsnet/Mail/alert3000/msg00718.html)

Takamizawa, K., 1998, {\it VSNET observations}, No.\ 10504 (available from \\
http://www.kusastro.kyoto-u.ac.jp/vsnet/Mail/obs10000/msg00504.html)

\end{document}

