[vsnet 2010] V844 Her preprint

[Taichi Kato <tkato>]

V844 Her preprint

Dear Colleagues,

   The following paper on V844 Her will appear as IBVS 4902.

   The figures are available under

   ftp://ftp.kusastro.kyoto-u.ac.jp/pub/vsnet/preprints/V844_Her/

Regards,
Taichi Kato
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\begin{document}

\IBVShead{xxxx}{xx April 2000}

\IBVStitletl{CCD PHOTOMETRY OF THE 1999 SUPEROUTBURST OF V844 HER}

\IBVSauth{T.~Kato$^1$, M.~Uemura$^1$}
\vskip 5mm

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

\IBVSobj{V844 Her}
\IBVStyp{UGSU}
\IBVSkey{Dwarf novae -- photometry}

\begintext

   V844 Her was discovered as a dwarf nova (Var43) by Antipin (1996).
Antipin (1996) 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 member 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$\pm$0.001 d, which made one of the shortest superhump periods
among SU UMa-type dwarf novae.  A more precise superhump period of
0.05597$\pm$0.00002 d is listed in 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 comparison 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.

\IBVSfig{8cm}{fig1.ps}{Overall light curve of V844 Her}

   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).

\IBVSfig{10cm}{fig2.ps}{Development of superhumps in V844 Her}

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{8cm}{fig3.ps}{Period analysis of 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 $\pm$ 0.00002 d,
corresponding to the frequency of 17.88 d$^{-1}$.  The present best period
well agrees with the previously determined period (Vanmunster 1997;
Patterson 1998).  The analysis for the period October 1 -- 3 yielded the
virtually same period (0.0559 $\pm$ 0.0001 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 yet
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.

\vskip 3mm

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

\begin{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 Wild Stars
    in the Old West}, p9, eds. S. Howell, E. Kuulkers, C. Woodward
    (ASP Conf. Series, 137)

Kato, T., Nogami, D., Baba, H., Masuda, S., Matsumoto, K., Kunjaya, C.,
    1999, {\it Disk Instabilities in Close Binary Systems}, p45, 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)

\end{references}

\end{document}

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