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\IBVShead{4902}{15 May 2000}

\IBVStitle{CCD Photometry of the 1999 Superoutburst of V844 H\lowercase{er}}

\IBVSauth{Kato, T.; Uemura, M.}

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

\SIMBADobjAlias{V844 Her}{Antipin V43}
\IBVStyp{ UGSU }
\IBVSkey{Dwarf novae - photometry}

\begintext

V844 Her was discovered as a dwarf nova (Var43) by Antipin (1996).  He
reported that the duration of the best-observed outburst is between 12
and 18 days, whose light curve closely resembled that of a
superoutburst of an SU UMa-type dwarf nova.  A systematic search for
further outbursts was carried out by members of various variable star
organizations, yielding the first ever detection by Scovil (1996) on
1996 Oct.~12.  Time-resolved CCD photometry by Vanmunster (1996) during
this outburst unambiguously detected superhumps, leading to a secure
classification of an SU UMa-type dwarf nova.  The determination of the
superhump period was first achieved during the next superoutburst in
1997 (Vanmunster 1997; Jensen 1997), yielding a period of
$0.056\pm0.001$ d, which resulted in one of the shortest superhump
periods among SU UMa-type dwarf novae.  A more precise superhump period
of $0.05597\pm0.00002$ d is listed by Patterson (1998).

Upon the detection by McGee (1999) of a bright outburst at visual
magnitude of 12.3 on 1999 September 29.824 UT, we started time-resolved
CCD photometry.  The observations were done using an unfiltered ST-7
camera attached to the Meade 25-cm Schmidt-Cassegrain telescope.  The
exposure time was 30 s.  The images were dark-subtracted, flat-fielded,
and analyzed using the Java$^{\rm TM}$-based aperture and PSF
photometry package developed by one of the authors (TK).  The flux of
the variable was measured relative to GSC 3062.32 (Tycho-2 magnitudes:
$V=10.57$, $B-V=1.25$), whose constancy was confirmed by comparing with
GSC 3062.281 ($V=12.79$, $B-V=1.03$, Henden and Sumner(1999)).  A total
of 1566 observations were obtained.  Heliocentric corrections were
applied to all observations before the following analysis.

Figure 1 illustrates the overall light curve of the present
observation.  Each point represents a nightly averaged magnitude with
an error bar indicating the standard error.  The light curve is
characteristic of an SU UMa-type superoutburst, showing the slowly
fading ``plateau'' stage, followed by an abrupt decline, and the final
fading.  The superhump signal was first detected on October 1
observation ($\sim 1.7$ d after the outburst detection), when the
amplitude of the signal was 0.09 mag.  Further observation on October 3
clearly showed fully grown superhumps with an amplitude of 0.3 mag (see
Figure~2).

The object entered a rapid decline stage on October 13 according to
observations reported to VSNET.  The data during the superoutburst
plateau (October 3--12) were analyzed, after subtracting the linear
decline, using the Phase Dispersion Minimization (PDM) method
(Stellingwerf 1978).

\IBVSfig{9cm}{4902-f1.ps}{Overall light curve of V844 Her}

\IBVSfig{12cm}{4902-f2.ps}{Period analysis of V844 Her}

\IBVSfig{9cm}{4902-f3.ps}{Development of superhumps in V844 Her}

The result of period analysis is given in Figure 3.  Although
unavoidable one-day aliases exist, we can safely choose, with the help
of previous period determinations, the correct period of
$0.05592\pm0.00002$~d, corresponding to the frequency of
17.88~d$^{-1}$.  The present best period agrees with the previously
determined period (Vanmunster 1997; Patterson 1998).  The analysis for
the period October 1--3 yielded practically the same period
($0.0559\pm0.0001$~d), which indicates the absence of a remarkable
period change during the superhump growth.

Besides superhumps, we examined the post-superoutburst behavior, during
which some SU UMa-type dwarf novae, especially systems with short
orbital systems (Kato et al.\ 1998), are known to show rebrightenings.
No evidence of rebrightening was observed, both in our CCD monitoring
until 15~d past the steep decline, and visual monitoring reported to
VSNET.

Aside from V485 Cen, almost all of SU UMa-type dwarf novae with the
shortest superhump (orbital) periods belong either to what is called
WZ Sge-type dwarf novae (Bailey 1979; Downes, Margon 1981; O'Donoghue
et al.\ 1991) and ER UMa-type dwarf novae (for a review, see Kato et al.\
1999).  The former category contains WZ Sge, AL Com, HV Vir, EG Cnc,
and related members LL And, SW UMa, WX Cet and T Leo.  The latter group
contains DI UMa and RZ LMi.  From available photometric materials
(Antipin (1996) and observations to VSNET), long and bright outbursts
(presumably superoutbursts) are separated by 220--290 d, without
detectable normal outbursts.  Such a low frequency of normal outbursts
resembles that of SW UMa, another SU UMa-type dwarf nova with a short
orbital period, but the relatively regular occurrence of superoutbursts
in V844 Her makes a slight difference.  It may be that V844 Her occupies
a previously unknown extension of WZ Sge-type dwarf novae toward
the short recurrence period.

\bigskip
The authors are grateful to all observers who reported observations to VSNET,
and especially to Hazel McGee who timely notified the outburst detection.

\references

Antipin, S. V., 1996, {\it IBVS}, No.\ 4360

Bailey, J., 1979, {\it MNRAS}, {\bf 189}, 41P

Downes, R. A., Margon, B., 1981, {\it MNRAS}, {\bf 197}, 35P

Jensen, L. T., 1997, {\it vsnet-obs circulation}, No.\ 5854 \\
(http://www.kusastro.kyoto-u.ac.jp/vsnet/Mail/obs5000/msg00854.html)

Henden, A., Sumner, B., 1999 \\
(ftp://ftp.nofs.navy.mil/pub/outgoing/aah/sequence/sumner/v844her.seq)

Kato, T., Nogami, D., Baba, H., Matsumoto, K., 1998, 
{\it ASP Conf. Series}, {\bf 137}, 9, {\it Wild Stars
in the Old West}, eds. S.\ Howell, E. Kuulkers, C. Woodward
%Changed: Fri Jun  3 09:50:40 MEST 2005

Kato, T., Nogami, D., Baba, H., Masuda, S., Matsumoto, K., Kunjaya, C.,
1999, {\it Disk Instabilities in Close Binary Systems}, p.\ 45, eds.\
S. Mineshige, J. C. Wheeler (Universal Academy Press, Tokyo)

McGee, H., 1999, {\it vsnet-alert circulation}, No.\ 3533 \\
(http://www.kusastro.kyoto-u.ac.jp/vsnet/Mail/alert3000/msg00533.html)

O'Donoghue, D., Chen, A., Marang, F., Mittaz, J. P. D., Winkler, H., 1991,
{\it MNRAS}, {\bf 250}, 363

Patterson, J., 1998, {\it PASP}, {\bf 110}, 1132

Scovil, C., 1996, {\it vsnet-obs circulation}, No.\ 4061 \\
(http://www.kusastro.kyoto-u.ac.jp/vsnet/Mail/obs4000/msg00061.html)

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

Vanmunster, T., 1996, {\it vsnet-obs circulation}, No.\ 4075 \\
(http://www.kusastro.kyoto-u.ac.jp/vsnet/Mail/obs4000/msg00075.html)

Vanmunster, T., 1997, {\it Cataclysmic Variables Circular}, No.\ 141 \\
(also http://www.kusastro.kyoto-u.ac.jp/vsnet/Mail/vsnet-alert/msg00935.html)


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