On the Raman O VI and related lines in classical novae

¹ Dipartimento di Fisica “Enrico Fermi”, Università di Pisa, 56127 Pisa, Italy
e-mail: shore@df.unipi.it
² INFN – Sezione Pisa, largo B. Pontecorvo 3, 56127 Pisa, Italy
³ Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany
⁴ Instituut voor Sterrenkunde, KU Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium
⁵ Max-Planck-Institut fuer extraterrestrische Physik, Giessenbachstraβe 1, 85741 Garching, Germany

Received: 9 August 2014
Accepted: 10 September 2014

Abstract

We critically examine the recent claimed detection of Raman-scattered O VI at around 6830 Å in the iron curtain stage spectra of the classical CO nova V339 Del. The observed line variations are compatible in the profile and timing of emission line strength with an excited state transition of neutral carbon. Line formation in classical nova ejecta is physically very different from what it is in symbiotic binaries, in which the O VI emission line is formed within the wind of the companion red giant at low differential velocity. The ejecta velocity and density structure prevent the scattering from producing analogous features. High velocity gradient outflows, such as winds, are subject to the same constraints. There might, however, be a broadband spectropolarimetric signature of the Raman process and also Rayleigh scattering at some stage in the expansion. We show that the neutral carbon spectrum, hitherto underexploited for novae, is especially useful as a probe of the structure of the ejecta during the early, optically thick stages of the expansion.