Electronic Telegram No. 906 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://cfa-www.harvard.edu/iau/cbat.html V2615 OPHIUCHI U. Munari, A. Siviero, and M. Valentini, Istituto Nazionale di Astrofisica, Padova Astronomical Observatory; and P. Ochner and S. Dallaporta, ANS ("Asiago Novae and Symbiotic stars") Collaboration, report that absolutely fluxed optical spectra (ranges 390-780 nm at 0.423 nm/pixel and 639-704 nm at 0.061 nm/pixel) of N Oph 2007 (cf. CBET 900; IAUC 8824) were obtained on Mar. 22.17 and 24.18 UT with the Asiago 1.82-m telescope (+ AFOSC). Large changes are seen to have occurred between these two dates: mainly a marked reduction in equivalent width of emission lines and reduction in outflow velocity of absorption components of P-Cyg profiles. On Mar. 22.17, the spectrum was characterized by emission lines of weak intensity, all displaying a P-Cyg profile. The strongest emission lines were due to Fe II multiplets 27, 28, 37, 38, 42, 48, 49, 55, and 74; Si II multiplets 2, 3, 4 and 5; N I multiplet 3; Ca II H and K; Na I D1 and D2; and O I 777.2-nm (the O I being the second strongest emission after H_alpha). The spectrum showed a large Balmer decrement, the observed H_alpha:H_beta:H_gamma emission ratio being 15.8:1.0:0.08. The integrated flux of the H_beta emission line was 3.2 x 10^(-12) erg cm^(-2) s^(-1). The emission component of H_alpha was gaussian in shape, with a FWHM of 940 km/s and an equivalent width of 3.73 nm. The absorption component had a flat bottom extending for 240 km/s, a width at half intensity of 540 km/s, and an equivalent width of 0.55 nm. With respect to the peak of the H_alpha emission, the absorption terminal velocity was -1415 km/s, and the mean velocity -910 km/s. In the Mar. 24.18 spectra, the lines have profoundly changed their appearance, with emission components of the P-Cyg profiles being just barely visible, and absorption components of Fe II lines having their equivalent widths reduced by 20 percent. The only emission lines apparent on a cursory inspection of the Mar. 24.18 spectra were O I 777.2-nm and H_alpha. The emission component of H_alpha shrank to 580 km/s in FWHM and to 0.75 nm in equivalent width. The terminal velocity of the absorption component remained stable around -1400 km/s, but its mean value slowed to -650 km/s, again with respect to the peak of the emission component. The H_alpha absorption component showed now a multi-component profile and, contrary to what is seen with the Fe II lines, the H_alpha component was not reduced in equivalent width, still holding at 0.55 nm. Diffuse interstellar bands were observed at 442.8, 578.0 (equivalent width 0.085 nm), 628.4 (0.27), and 661.4 (0.021) nm. CCD photometry for Mar. 22.16 gives V = 9.46 (+/- 0.02) and B-V = +0.89 (+/- 0.02). NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2007 CBAT 2007 March 25 (CBET 906) Daniel W. E. Green