Sn 2006jc: a Wolf-rayet Star Exploding in a Dense He-rich Circumstellar Medium

We present optical photometry and spectra of the peculiar type Ib supernova (SN) 2006jc. Strong He I emission lines indicate the progenitor star exploded inside a dense circumstellar medium (CSM) rich in He. An exceptionally blue continuum persists from our first spectrum obtained 15 days after discovery through our last spectrum ∼1 month later. Based on the presence of isolated Fe II emission lines, we interpret the blue continuum as fluorescent Fe emission, although we do not understand the cause of this unusual fluorescence. The red He I line profiles are double peaked, suggesting that the CSM has a highly aspherical geometry. The He I lines that are superposed on the blue continuum show P-Cygni profiles, while the redder He I lines do not, implying that the blue continuum is related to the aspherical geometry. The He-rich CSM, aspherical geometry, and a recent coincident luminous outburst indicate that the progenitor star was a WNE Wolf-Rayet (WR) star, possibly transitioning from the luminous blue variable stage. We also present unpublished spectral and photometric data of SN 2002ao, which along with SN 1999cq, is very similar to SN 2006jc. We propose these three objects may represent a new and distinct class of SNe with dense environments around WR stars. Subject headings: circumstellar matter, stars winds, stars Wolf-Rayet, supernovae general, supernovae individual (SN 2006jc; SN 1999cq; SN 2002ao)