On the Raman O VI and related lines in classical novae

TL;DR

This paper critically evaluates the claimed detection of Raman scattered O VI in a classical nova, arguing that observed features are more consistent with neutral carbon emission and discussing implications for nova ejecta analysis.

Contribution

The study refutes previous claims of Raman O VI detection in novae and highlights the diagnostic potential of neutral carbon spectra for ejecta structure analysis.

Findings

Observed line variations match neutral carbon transitions, not Raman scattering.

Ejecta velocity and density prevent Raman scattering features in classical novae.

Neutral carbon spectra can probe early ejecta structure during expansion.

Abstract

We critically examine the recent claimed detection of Raman scattered O VI at around 6830\AA\ in the iron curtain stage spectra of the classical CO nova V339 Del. The observed line variations are compatible in 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 that 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. 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 under-exploited for novae, is especially useful as a probe of the structure of the ejecta during the early, optically thick stages of the expansion