[vsnet-alert 7557] V844 Her outburst

[Taichi Kato <tkato@kusastro.kyoto-u.ac.jp>]

V844 Her outburst

   The short-period SU UMa-type (superhump period 0.05592 d) dwarf nova
V844 Her is undergoing a relatively rare outburst as reported by
Eddy Muyllaert, Patrick Schmeer and Hazel McGee.

   The all recorded outbursts of V844 Her have been superoutbursts.
Intensive time-series coverage of the present outburst is highly encouraged!

   The last outburst (superoutburst) was in 2002 May.  The interval of
the outbursts has become shorter than the pervious values.
If this outburst turns out to be a normal outburst, this makes the first
occasion in V844 Her.

[excerpt from Kato and Uemura (2000) IBVS 4902]

   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.

   See also Thorstensen et al. (2002) PASP in press, astro-ph/0206426
for radial-velocity studies.

Regards,
Taichi Kato
VSNET Collaboration team

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