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\IBVShead{4227}{14 August 1995}

\centerline{\ft DH AQUILAE -- A NEW SU UMa-TYPE DWARF NOVA}

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\begintext

   After discovery as a variable star, DH Aql was confirmed
to be a large-amplitude dwarf nova by Tsessevich (1969).  He
observed three outbursts from 268 Sternberg plates.  These outbursts
were all short-lived (lasting less than a few days), accompanied
by a rapid decline up to 1.3 mag day$^{-1}$.  He deduced from these
observations the outburst cycle length of DH Aql as 268 days.
The General Catalogue of Variable Stars (GCVS) adopted these
outburst parameters and UGSS-type classification.  Zhukov and
Solovjev (1972) also reported a similar short outburst in 1972.
A similar conclusion was obtained by more recent visual monitoring.
Vanmunster and Howell (1995) list only three confirmed outbursts for
the period 1991--1994.  A photoelectric photometry (V=18.25)
during quiescence (Bruch and Engel 1994) suggests a large outburst
amplitude of $\sim$ 5.7 mag.

   All the above facts -- 1) a large outburst amplitude,
2) existence of short outbursts with a rapid decline, 3) low outburst
frequency -- seem to suggest SU UMa-type classification rather than
SS Cyg-type suggested in GCVS, despite the fact that long outbursts
suggesting superoutbursts seem to be missing at least from available
literature.


   Szentasko, Vanmunster and others distributed alert notices
of a bright outburst of DH Aql via vsnet.  The peak brightness
(m$_v$=12.4) seemed to surpass most of the historical outbursts,
so we started
{\it V}-band CCD photometry in order to check whether this outburst
is a superoutburst.


   The observations were done on Sep. 23 and 25, 1994
using a CCD camera (Thomson, TH~7882CDA, $576 \times 384$ pixels
with 23 $\mu$m square pixel size) attached to the Cassegrain focus
of 0.6-m reflector (focal length=4.8m) 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 mode of $2 \times 2$ on-chip summation was employed.
The exposure time was 60$-$90 sec and saving dead time
of 13 sec throughout observations.

We reduced the data using the personal-computer-based aperture
photometry package developed by one of the authors (T.K.).
This package automatically subtracts bias-frames, applies flat
fielding and enables us to estimate the instrumental magnitudes.
The aperture size was 9$''$ in radius. The sky level was determined
from pixels whose distance from the individual objects are
between 24$''$ to 48$''$.

An identification chart of DH Aql based on our CCD image is drawn in Figure 1.
Figure 2 shows the light curve of DH Aql on Sep. 25, 1994
with the differential magnitude of DH Aql and the star \lq\lq C$_1$''
in Figure 1.  The detection of superhumps clearly seen in Figure 2
and the long duration (at least 14 days) of the present outburst
(Mattei 1995) indicate that this outburst is doubtlessly a superoutburst.
We analysed the  Sep. 25 light curve, using phase dispersion
minimization (PDM) method (Stellingwerf 1978) implemented in IRAF
package (IRAF is distributed by National Optical Astronomy
Observatories, U.S.A.) and obtained 0.0805 ($\pm$ 0.003) day
as the best estimation of superhump period.
The present observations first established DH Aql as an SU UMa-type
dwarf nova.

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\centerline{2}
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\begin{center}
Figure. 1. Field map of DH Aql.  The field of view is about
6$\times$9 arcmin.  The variable (DH) and comparison (C$_1$) are
marked.
\end{center}

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\centerline{\epsffile{4227-f2.ps}}
\begin{center}
Figure. 2. Time-resolved photometry at Ouda on Sep. 25, 1994.
Superhumps with a period of 0.0805 day are clearly seen.
\end{center}
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\centerline{3}
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The authors are grateful to VSNET members, especially L. Szentasko
and T. Vanmunster for notifying us of the outburst, and F. Ringwald
for searching the references using SIMBAD database.
We are also grateful to P. Schmeer and AFOEV (Schweitzer) for
supplying us with additional outburst records.
Part of this work is supported by a Research Fellowship of the Japan
Society for the Promotion of Science for Young Scientists (T.K).
\vskip 1cm
\beginauthors
\authorsrightcol
Daisaku NOGAMI
Taichi KATO
Dept. of Astron., Faculty of Sci.
Kyoto University
Sakyo-ku, Kyoto 606-01 Japan
\endauthors

\references


  Bruch, A., Engel, A., 1994, {\it Astron. Astrophys. Suppl.}, {\bf 104}, 79

  Ohtani, H., Uesugi, A., Tomita, Y., Yoshida, M., Kosugi, G.,
     Noumaru, J., Araya, S., and Ohta, K., 1992, {\it Mem. Fac. of Sci.,
     Kyoto Univ., Series A of Physics, Astrophysics,Geophysicsand
     Chemistry}, {\bf 38}, 167

  Mattei, J. A., 1995, Observations from the AAVSO International
         Database, private communication

  Stellingwerf, R. F., 1978, {\it ApJ}, {\bf 224}, 953

  Tsessevich, V. P., 1969, {\it Astron. Tsirk.}, No.\,529

  Vanmunster, T., Howell, S. B., 1995, ``Outburst Activity Data on Selected Cataclysmic
     Variables"

  Zhukov, G. V., Solovjev, V. Ya., 1972, {\it Astron. Tsirk.}, No.\,729

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