[IAUC] CBET 775: 20061218 : V2362 CYGNI

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                                                  Electronic Telegram No. 775
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
M.S. 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
IAUSUBS en CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions)
CBAT en CFA.HARVARD.EDU (science)
URL http://cfa-www.harvard.edu/iau/cbat.html


V2362 CYGNI
     U. Munari, M. Valentini, and A. Siviero, Istituto Nazionale di
Astrofisica, Padova Astronomical Observatory; A. Henden, AAVSO; and P.
Valisa, A. Stanzione, S. Dallaporta, G. Cherini, S. Moretti, and S.
Tomaselli, ANS ("Asiago Novae and Symbiotic stars") Collaboration, report
that, following the conclusion on Nov. 30 (cf. CBET 769) of the long-
lasting re-brightening phase that started in July (cf. CBET 671), V2362
Cyg (= N Cyg 2006) has entered a rapid decline that has reached its
fastest speed around Dec. 11.5 UT, when the decline rate had peaked at
0.7 mag/day in the B band.  Since then, the decline has slowed, and the
rate around Dec. 15.0 is only 0.1 mag/day in the B band.  Overall, the
recent decline phase has taken the nova from B = 10.46, B-V = +0.48,
V-R_c = +0.62, and R_c-I_c = +0.54 on Nov. 30.2 to B = 13.75, B-V = +0.41,
V-R_c = +1.16, and R_c-I_c = +0.53 on Dec. 15.73.  The sudden acceleration
in the photometric evolution has been parallelled by dramatic and rapid
changes in the spectral appearance, as well.  Echelle-mode, high-S/N,
absolutely-fluxed spectra (range 350-890 nm), obtained with the Asiago
1.82-m telescope (+ AFOSC) on Dec. 14.7, show that the nova has now
entered the nebular stage and that the ionization is increasing.  Observed
emission lines include He I 706.5-, 667.8-, 587.6-, 501.6-, and 447.1-nm;
O I 777.2- and 844.6-nm; [O I] 630.0- and 636.4-nm; [O II] 732.5-nm; [O
III] 436.3-, 495.9-, and 500.7-nm; C II 426.7- and 723.4-nm; N I 821.2-
and 868.3-nm; N II 500.1- and 567.4-nm; [N II] 575.5-nm; N III 453.4- and
464.4-nm; Ca II 854.2-nm; and various Fe II and [Fe III] at 464.4 and
527.0 nm.  The Balmer series is fully developed from H_alpha to H_9, and
higher terms merge into the Balmer continuum in emission.  The integrated
H_beta flux is 9.5^(-12) erg/cm^2/s.  Emission lines present saddle-like
profiles, with a velocity separation of the blue and red peaks of 860 km/s
for He I and [NII], 820 km/s for Balmer and O I, 760 km/s for [O III], and
620 km/s for [O I].  The FWHM of a Gaussian fit to the whole emission line
profile is 1130 km/s for [O I], 1250 km/s for He I, 1330 km/s for the
Balmer lines, 1400 km/s for [N II], and 1610 km/s for [O II].


NOTE: These 'Central Bureau Electronic Telegrams' are sometimes
      superseded by text appearing later in the printed IAU Circulars.

                         (C) Copyright 2006 CBAT
2006 December 18                 (CBET 775)               Daniel W. E. Green