Central Bureau for Astronomical Telegrams
IAUC 7678: WZ Sge
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Circular No. 7678
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions)
CBAT@CFA.HARVARD.EDU (science)
URL http://cfa-www.harvard.edu/iau/cbat.html ISSN 0081-0304
Phone 617-495-7440/7244/7444 (for emergency use only)
WZ SAGITTAE
T. Kato, H. Ohashi, R. Ishioka, M. Uemura and K. Matsumoto, Kyoto
University; G. Masi, Ceccano, Italy; D. Starkey, Auburn, Indiana;
J. Pietz, Erftstadt, Germany; and B. Martin, The King's University College,
Edmonton, Alberta, on behalf of the VSNET collaboration team, report:
"Our time-resolved CCD photometry revealed that WZ Sge started to show a
different type of prominent modulations (amplitude 0.10 mag) on Aug.
4.53 UT. Between Aug. 4.44 and 5.08 the oscillations had an initial period
of 0.057143 +/- 0.000046 day, which is 0.8 percent longer than the orbital
period (0.05669 day). Earlier observations, starting on Aug. 4.163, also
showed a suggestion of the growing signal. Later observations, between
Aug. 5.166 and 6.074, have shown further development of superhumps
up to 0.23 mag and give a mean period of 0.058876 +/- 0.000025 day.
The sharply defined profile and the period excess qualify the present
variations as genuine superhumps. The superhumps developed from the
secondary hump structure of the early superhumps (IAUC 7672).
The 12-day delay of superhump evolution since the start of the outburst is
the longest one measured among all known SU UMa-type dwarf novae. The
observed delay is consistent with the earliest time of detection of a
similar, but less distinct, signal during the 1978 outburst (Heiser and
Henry, IBVS 1559)."
H. Baba, National Astronomical Observatory of Japan; K.
Sadakane, Osaka-Kyoiku University; Y. Norimoto, Okayama
Astrophysical Observatory (OAO); and D. Nogami, K. Matsumoto,
M. Makita and T. Kato, Kyoto University, report:
"We constructed Doppler tomograms of WZ Sge using time-resolved
spectra (resolution about 3000) covering two binary orbits between
July 24.576 and 24.701 UT with the OAO 0.91-m telescope (IAUC
7672). The He II (468.6 nm) map shows that the emitting region on
the accretion disk is elongated along the ballistic stream, which
constitutes an asymmetric 'boomerang-like' one-armed spiral
structure. The present observation shows the earliest detection
of presence of the spiral structure of the emission line. Since
Steeghs et al. (IAUC 7675) reported that the He II and C III
emission lines were dominated by a two-armed spiral pattern four
days after the maximum, there must have been a dramatic change in
the emission pattern between our earlier observation and theirs.
Such a totally unprecedented, unexpected change may be responsible
for the growth of early superhumps."
(C) Copyright 2001 CBAT
2001 August 6 (7678) Brian G. Marsden
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