2002MNRAS.330..844S

We report the detection of a very narrow P Cygni profile on top of the broad emission Hα and Hβ lines of the Type IIn Supernova 1997eg. A similar feature has been detected in SN 1997ab, SN 1998S and SN 1995G. The detection of the narrow P Cygni profile indicates the existence of a dense circumstellar material (CSM), into which the ejecta of the supernova is expanding. From the analysis of the spectra of SN 1997eg we deduce (i) that such CSM is very dense (n ≳5x10⁷ cm^–3), (ii) that it has a low expanding velocity of about 160km.s^–1. The origin of such dense CSM can be either a very dense progenitor wind (M{dot} ∼10^–2 M_☉yr^–1) or a circumstellar shell product of the progenitor wind expanding into a high-pressure environment.