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IAUC 7669: WZ Sge

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                                                  Circular No. 7669
Central Bureau for Astronomical Telegrams
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions)
URL http://cfa-www.harvard.edu/iau/cbat.html  ISSN 0081-0304
Phone 617-495-7440/7244/7444 (for emergency use only)

     R. Ishioka, M. Uemura, K. Matsumoto, and T. Kato, Kyoto
University; K. Ayani, Bisei Astronomical Observatory (BAO); and H.
Yamaoka, Kyushu University, on behalf of the VSNET collaboration
team and the Variable Star Observers League in Japan, report:  "WZ
Sge is undergoing its first outburst since 1978 (cf. IAUC 3311), as
indicated by the following visual magnitude estimates:  July 23.565
UT, 9.7 (T. Ohshima, Gifu, Japan); 23.597, 9.4 (H. Itoh, Tokyo,
Japan); 23.600, 9.6 (H. Maehara, Saitama, Japan); 23.622, 9.8 (T.
Watanabe, Shizuoka, Japan); 23.716, 8.6 (Itoh); 23.843, 8.7.  CCD
time-resolved photometry at Kyoto University on July 23.6-23.8
showed a rapid brightening from mag 9.7 to 8.7 within 5 hr.  Short-
term modulations with timescales of 0.01-0.03 day were superimposed
on the rapidly rising trend.  These modulations will grow into
'early superhumps', which are observed in early stages of the
outburst of WZ Sge-type stars (cf. IAUC 6164, 6517, 7552).  A
preliminary spectrum (range 450-670 nm) of WZ Sge on July 23.74
(taken by Ayani with the BAO 1.01-m telescope) shows H-alpha and
H-beta lines in absorption on a blue continuum.  This feature
differs from one at 1978 outburst (Brosch et al. 1980, Ap.J. 236,
L29; Oltorani et al. 1980, A.Ap. 87, 31), when the H-alpha line was
observed as emission (on the day that the outburst was detected)
and became stronger in its intensity with time."
     J. A. Mattei, AAVSO, also reports that, according to
observations in the AAVSO International Database, the last outburst
of WZ Sge occurred on 1978 Dec. 1, when the star reached mag 8.0;
it slowly faded to mag 10.8 by Dec. 30, with prominent superhump
oscillations of several tenths of a magnitude throughout.  On 1978
Dec. 31, the variable faded abruptly to mag 12.5 and then recovered
to 11.1 by 1979 Jan. 3, before slowly fading to minimum by Apr.
1979.  Earlier outbursts of WZ Sge include 1913 (when it reached
m_pg = 7.0) and 1946 (when it reached m_v = 8.0).  Recent visual
magnitude estimates of WZ Sge submitted to the AAVSO and/or to the
Central Bureau:  July 20.061 UT, 15.4 (G. Poyner, Birmingham,
England); 22.969, 15.3 (M. Reszelski, Szamotuly, Poland); 23.030,
[13.6 (H. McGee, West Clandon, Surrey, England); 23.876, 8.1 (C.
Jones, Laindon, Essex, England); 23.886, 8.4 (P. Schmeer,
Bischmisheim, Germany); 23.895, 8.6 (R. J. Bouma, Groningen, The
Netherlands); 23.922, 8.6 (Poyner); 24.013, 7.9 (F. Vohla,
Altenburg, Germany); 24.050, 8.1 (G. Comello, Groningen,
Netherlands; 24.105, 8.0 (J. Bortle, Stormville, NY); 24.244, 8.2
(R. Royer, Lakewood, CA).  CCD V magnitudes by J. D. West, Mulvane,
KS:  July 24.110, 7.95; 24.126, 8.41 (comparison star HD 191083, V
= 8.76).

                      (C) Copyright 2001 CBAT
2001 July 24                   (7669)            Daniel W. E. Green

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