2010CBET.2204....3M

U. Munari and A. Siviero, Istituto Nazionale di Astrofisica, Astronomical Observatory of Padova; and P. Valisa and S. Dallaporta, "Asiago Novae and Symbiotic Stars" (ANS) collaboration, report that they obtained absolutely fluxed, low-resolution spectra of V407 Cyg on Mar. 13.09 UT with the Asiago 1.22-m telescope (range 325-753 nm; 0.23 nm/pixel) and the Varese 0.6-m telescope (380-840 nm; 0.21 nm/pixel), and echelle spectroscopy (range 395-865; resolving power 10000) with the latter instrument also. The spectral appearance is a highly peculiar one. The spectrum is completely different from those ever recorded for this object and other symbiotic Mira variables in outburst. The absorption spectrum of the Mira star is completely overwhelmed by the blue continuum from the outbursting component, with Balmer continuum in emission. The profiles of the emission lines belong to two distinct groups, the first originating from the ionized slow wind of the Mira, the other from the fast expanding ejecta of the nova outburst, a scenario reminiscent of the symbiotic recurrent nova RS Oph. The first emission-line group is made by sharp (FWHM 60 km/s) and weaker lines, similar to those usually visible in quiescence. The Balmer emission lines display the classical central absorption usually observed in symbiotic stars – and in V407 Cyg, in particular. He I lines are present, too, in this group without the central reversal. In addition, the outburst brought a huge forest of sharp Fe II lines (not normally present in quiescence) and the disappearance of [O III] and [N II] nebular lines. The second group of lines is characterized by a wide Gaussian profile (FWHM 2300 km/s) and is present in the Balmer series and He I lines. Thus, the Balmer and He I lines display simultaneously both type of profiles: the broad component, with on top the sharp one. The integrated flux of the H_beta broad component is ten times that of the sharp one, and three times for H_alpha. The broad component looks closely similar to the spectrum of He/N classical novae. The authors believe that the white dwarf companion to the Mira variable is experiencing an outburst similar to that of classical novae, and its ejecta are moving in the circumstellar environment already filled by the ionized wind of the Mira, with associated shocks and presumably hard x-ray emission. The typical outbursts of known symbiotic binaries, and symbiotic Miras in particular, are characterized by a very slow rise (months) and no significant mass ejection, with the notable exceptions of RS Oph and T CrB. Perhaps V407 Cyg will join them in an special class of objects; if so, we might anticipate a very rapid evolution and the necessity of a fast observational response. On Mar. 13.1 UT, the authors measured V = 8.671, B-V = +0.988, V-R_c = +1.582, V-I_c = 2.635.