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Discovery of coronal emission lines in V407 Cyg

ATEL # 2546; U. Munari, A. Siviero (INAF Padova-Asiago), P. Valisa (ANS Collaboration)
on 11 Apr 2010; 22:05 UT
Password Certification: Ulisse Munari (ulisse.munari@oapd.inaf.it)

Subjects: Optical, Binaries, Cataclysmic Variables, Nova, Variables

We report about discovery of [FeX] 6375, [FeXI] 7890, [ArX] 5535 and [NiXII] 4233 Ang coronal emission lines in V407 Cyg, which are steadily increasing in intensity with time.

V07 Cyg is a symbiotic binary harboring a Mira variable, of 745 day pulsation and a possible orbital period of 43 years, at a distance of 2.5/3.0 kpc and a reddening of E(B-V)=0.5/0.6 (Munari et al. 1990, MNRAS 242, 653). Mira of such a long pulsation period are generally OH/IR sources, with a thick dust envelope which prevents direct observation of the central star. In addition to a possible previous one in 1936 (when the object was noted for the first time by Hoffmeister 1949, VVS 1, 295), V407 Cyg has been recently discovered in outburst by Nishiyama and Kabashima (2010, CBET #2199) on Mar 10.8 UT. Spectroscopic confirmation was first provided by Munari et al. (2004, CBET #2204) on Mar. 13.1 UT. They noted the emergence of the spectrum of a He/N nova that overwhelmed the absorption spectrum of the Mira. Numerous and strong emission lines were observed, which belonged to two distinct groups. The first group, composed by sharp profiles with even narrower central absorptions, originated from the ionized slow wind of the Mira. The second group, characterized by much broader profiles for helium, nitrogen and hydrogen lines , originated from the nova fast expanding ejecta. Such a scenario was highly reminiscent of the recurrent nova RS Oph. The outburst of V407 Cyg has since then been detected also in gamma-rays (ATel #2487) and at radio wavelengths (ATel #2506, ATel #2511, ATel #2514, ATel #2536), and observed in the infrared (CBET #2210).

Our tight Echelle high-resolution monitoring of the spectral evolution of V407 Cyg traces the first appearance of the coronal emission lines around March 17, when [FeX] 6375 Ang had an equivalent width of about 4 Ang. Since then its equivalent width has steadily increased, reaching 17, 24, 36, 49 and 61 Ang on Mar 23, 28, Apr 2, 7 and 10, respectively. The FWHM has remained moderately stable around 600 km/sec over. Other coronal lines present in V407 Cyg are [FeXI] 7890, [ArX] 5535 and [NiXII] 4233. As of April 10, [NiXIII] 5116 and [FeXIV] 5303 are not detected. The coronal line spectrum of V407 Cyg resemble quite closely that observed in RS Oph during its 2006 outburst.


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