Electronic Telegram No. 1379
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
M.S. 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://www.cfa.harvard.edu/iau/cbat.html


V2491 CYGNI
     L. A. Helton and C. E. Woodward, University of Minnesota; and K.
Vanlandingham and G. J. Schwarz, West Chester University, report on
Boller-and-Chiven spectroscopic observations (range 380.0-900.0 nm;
resolution about 0.28 nm) of V2491 Cyg (cf. IAUC 8934, CBET 1354) obtained
at the Steward Observatory Bok 2.29-m telescope on Apr. 27.3 and 28.4 UT.
The spectra show strong emission from the Balmer series of hydrogen with
very high velocity widths:  4200 km/s for H_alpha, 4700 km/s for H_beta,
and 5400 km/s for the weaker Balmer transitions.  The velocity width of
H_alpha has continued to decline, while the width of H_beta has increased
relative to that reported by Tomov et al. (http://www.astronomerstelegram.org/
?read=1475).  The strongest non-Balmer line is the He II 468.6-nm/N III
464.0-nm blend, with other He/N blending at He I 447.1-nm/N II 448.9-nm
and He I 501.6-nm/N II 500.1-nm, thus supporting the conclusions of Tomov
et al. (http://www.astronomerstelegram.org/?read=1485) that this is a 'He/N'
nova of type Pn.  There also appears to be broad Na I D emission at 589.0
nm and O I at 844.6 nm.  The line profiles are no longer flat-topped and
symmetric but appear rounded with a strong blue peak.  The O I 844.6-nm/
H_beta flux ratio has declined to 0.46 (op.cit.).  P-Cyg profiles are
no longer present.  Using the reddening of E(B-V) = 0.43 reported by Rudy
et al. (IAUC 8938), a distance of 10.5 kpc is estimated using the MMRD
relation of Della Valle and Livio (1995, Ap.J. 452, 704).
     Photoelectric and CCD magnitudes (unfiltered unless otherwise noted):
Apr. 21.023 UT, 10.0 (L. Urbancok, SAO Observatory Sid, Slovakia); 24.052,
9.3 (Urbancok); 27.017, V = 9.937 +/- 0.015, B-V = -0.06 +/- 0.03 (M. M. M.
Santangelo, Capannori, Italy, 0.30-m telescope + SSP-5A photometer;
comparison star HDE 331152);
      Visual magnitude estimates (cf. IAUC 8935; CBET 1354):  Apr. 24.075 UT,
9.6 (K. Hornoch, Vohancice, Czech Republic); 24.949, 9.5; 26.137, 9.6 (P.
Schmeer, Bischmisheim, Germany); 27.132, 10.1 (Schmeer); 28.135, 10.8
(Schmeer); 28.913, 11.4 (Hornoch); May 3.941, 11.6 (Hornoch); May 6.917, 11.9
(Hornoch);.


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      superseded by text appearing later in the printed IAU Circulars.

                         (C) Copyright 2008 CBAT
2008 May 17                      (CBET 1379)              Daniel W. E. Green