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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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