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\IBVShead{4163}{22 February 1995}


\centerline{\ft OBSERVATIONS OF A NEWLY DISCOVERED}
\centerline{\ft SU UMa-TYPE STAR HV AURIGAE}
\vspace{.4cm}
\begintext

HV Aurigae was discovered to be a dwarf nova by Hoffmeister (1964) in Dec.
1963.  He also found two outbursts on the Palomar charts occurred in March 1940 and March 1941 
on the Palomar charts.  After the discovery, the object has been little
studied except the additional observations of two outbursts and
a finding chart given by Bruch et al. (1987).  The quiescent
identification was made by Downes and Shara (1993).
\par

Many of the outbursts of HV Aur have probably been overlooked because of its
faintness, because the maximum visual magnitude in outburst is only about 15.
However, an outburst was recently noticed by M. Iida (Variable Star
Observers League in Japan) on Nov. 8, 1994, and announced a brightness
variation which was regarded to be superhumps (M. Iida 1995, in preparation).
\par

In order to confirm the superhumps and to determine the superhump period,
we made observations on Nov. 11 and 13, 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 observation lasted about six and eight hours on Nov. 11 and 13,
respectively, occasionally interrupted by clouds.
The exposure time was 120 sec with a read-out 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-flames, applies flat fielding
and enables us to estimate the instrumental magnitudes.
The aperture size was 8$''$ in radius. The sky level was determined from
pixels whose distance from the individual objects are between 16$''$ to 30$''$.


Figures 1 and 2 show short-term light curves of differential magnitude
between HV Aur and a comparison star (Table 1). The zero point of
the ordinate of figures corresponds to {\it V} = 13.6.  The abscissa is
Julian Day minus 2449660.


\vskip 1mm
\begin{center}
Table 1. The coordinates and magnitudes of the comparison and
check stars taken from Guide Star Catalog (GSC).
\end{center}
\vskip 1mm
 \begin{center}
  \begin{tabular}{|c||c|c|c|}
   \hline
           & R. A.(J2000) & Dec.(J2000) & m$_{\rm V}$ \\ \hline\hline
comparison & 04\fh 53\fmm 02\fss 97  &
	 +38\degr 18\farcmm 10\farcs 0 & 13.6 \\ \hline
check  1   & 04\fh 53\fmm 00\fss 06  &
	 +38\degr 14\farcmm 22\farcs 0 & 13.4 \\ \hline
check  2   & 04\fh 53\fmm 06\fss 31  &
	 +38\degr 13\farcmm 50\farcs 9 & 14.3 \\ \hline
check  3   & 04\fh 53\fmm 13\fss 20  &
	 +38\degr 18\farcmm 20\farcs 9 & 14.5 \\ \hline
  \end{tabular}
 \end{center}
\vfill \eject

\centerline{2}
\epsfysize=10cm
\centerline{\epsffile{4163-f1.ps}}
\centerline{Figure 1: The short term light curve of HV Aur on Nov. 11 1994}
\epsfysize=10cm
\centerline{\epsffile{4163-f2.ps}}
\centerline{Figure 2: The short term light curve of HV Aur on Nov. 13 1994}
\vfill \eject

\centerline{3}
\epsfysize=10cm
\centerline{\epsffile{4163-f3.ps}}
\centerline{Figure 3: Theta diagram by PDM; the minimum point corresponds
to 0.0855 day}
\vskip 2mm
Using three nearby check stars selected from GSC, we confirmed
the constancy of the comparison star (Table 1) within
0\fm 02, and the r.m.s. error for a single
measurement of the differential magnitude is 0\fm 02.
Although the error is a little bit large because of clouds,
the hump-like feature is considered to be real because its amplitude
is about 0.2 mag, being much larger than the estimated error.

By analyzing the light curve using PDM (Stellingwerf 1978) program within
IRAF package (IRAF is distributed by the National Optical Astronomy
Observatories, U.S.A.), after removing the trend of linear decline,
we obtained 0.0855 $\pm$ 0.0001 day as the best estimate of the period.
Figure 3 shows the $\Theta$ diagram, whose abscissa is frequency ($day^{-1}$).
We regarded the feature as superhumps, because the shape of the modulation,
rather rapid rise and following gradual decline, is characteristic of
a superhump of SU UMa-stars in superoutburst and only a superhump can
explain such large amplitude modulation in a dwarf nova in outburst.
We thus confirmed Iida's identification of HV Aur as a new member of
SU UMa-type dwarf novae, and obtained a superhump period of 0.0855 day.


The decline rate is 0.035 mag day$^{-1}$, which is about one fourth
of those typically observed in slow decline phase of usual SU UMa stars.
More observation is necessary to reveal the nature of this peculiarity.

The authors are grateful to M. Iida for notifying us of the outburst
and calling our attention to this interesting dwarf nova.
This research has been partly supported by Research Fellowship of the
Japan Society for the Promotion of Science for Young Scientists (T.K.).

\vskip 6mm

\beginauthors
Daisaku NOGAMI
Taichi KATO
Seiji MASUDA
Ryuko HIRATA
\authorsrightcol
Department of Astronomy,
Faculty of Science, Kyoto University
Sakyo-ku, Kyoto 606-01, Japan
\endauthors
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\centerline{4}
\vskip 4mm
\noindent e-mail address:

\noindent nogami@kusastro.kyoto-u.ac.jp                       %email


\noindent tkato@kusastro.kyoto-u.ac.jp                       %email


\noindent masuda@kusastro.kyoto-u.ac.jp                       %email

\vskip 8mm

\references

Bruch, A., Fischer, F. J., and Wilmsen, U., 1987, {\it Astron.
Astrophys. Suppl.}, {\bf 70}, 481

Downes, R. A., and Shara, M. M., 1993, {\it Publ. Astron. Soc.
Pacific}, {\bf 105}, 127

Hoffmeister, C., 1964, {\it Astron. Nachr.}, {\bf 288}, 49

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, Geophysics and Chemistry}, {\bf 38}, 167

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

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