DISCOVERY OF PRECURSOR LUMINOUS BLUE VARIABLE OUTBURSTS IN TWO RECENT OPTICAL TRANSIENTS: THE FITFULLY VARIABLE MISSING LINKS UGC 2773-OT AND SN 2009ip

Abstract

We present progenitor-star detections, light curves, and optical spectra of\nSN2009ip and the 2009 optical transient in UGC2773 (U2773-OT), which were not\ngenuine SNe. Precursor variability in the decade before outburst indicates that\nboth of the progenitor stars were LBVs. Their pre-outburst light curves\nresemble the S Doradus phases that preceded giant eruptions of eta Carinae and\nSN1954J (V12 in NGC2403), with intermediate progenitor luminosities. HST\ndetections a decade before discovery indicate that the SN2009ip and U2773-OT\nprogenitors were supergiants with likely initial masses of 50-80 Msun and\n$\\ga$20 Msun, respectively. Both outbursts had spectra befitting known LBVs,\nalthough in different physical states. SN 2009ip exhibited a hot LBV spectrum\nwith characteristic speeds of 550 km/s, plus faster material up to 5000 km/s,\nresembling the slow Homunculus and fast blast wave of eta Carinae. U2773-OT\nshows a forest of narrow absorption and emission lines comparable to that of S\nDor in its cool state, plus [CaII] emission and an IR excess indicative of\ndust, similar to SN2008S and N300-OT. [CaII] emission is probably tied to a\ndusty pre-outburst environment, and not the outburst mechanism. SN2009ip and\nU2773-OT may provide a critical link between historical LBV eruptions, while\nU2773-OT may provide a link between LBVs and SN2008S and N300-OT. Future\nsearches will uncover more examples of precursor LBV variability of this kind,\nproviding key clues that may help unravel the instability driving LBVs.\n