| Discovery of Precursor LBV Outbursts in Two Recent Optical Transients: The Fitfully Variable Missing Links UGC 2773-OT and SN 2009ip (2009) | |||||||||
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| We present progenitor star detections, light curves, and spectra of SN 2009ip and the 2009 optical transient in UGC 2773 (U2773-OT), which were not genuine supernovae (SNe). In particular, precursor variability in the decade before outburst indicates that both of these progenitor stars were luminous blue variables (LBVs). Their pre-outburst light curves resemble the S Doradus phases that preceded giant eruptions of the prototypical LBVs eta Car and SN 1954J (V12 in NGC 2403), and their progenitor luminosities are between those of eta Car and V12. HST detections a decade before discovery indicate that the SN 2009ip and U2773-OT progenitors were supergiants with likely initial masses of 50--80 Msun and ~>20 Msun, respectively. Both objects had spectra befitting known LBVs, although in different physical states. The spectrum of U2773-OT shows a forest of narrow absorption and emission lines comparable to S Dor in its cool state, but also exhibits [Ca II] emission and infrared excess emission indicative of dust, similar to SN 2008S and the 2008 optical transient in NGC 300 (N300-OT), whereas SN 2009ip showed none of these features. Yet, both SN 2009ip and U2773-OT are clearly LBVs. We propose, therefore, that the presence of [Ca II] emission is tied to a dusty pre-outburst environment, which may or may not be present around any particular LBV, and is not a distinguishing property of the outburst mechanism. Infrared luminosities for the obscured progenitors of SN 2008S and N300-OT, while faint compared to eta Car, are comparable to the apparent progenitor luminosities of U2773-OT, V12, and other LBVs. Thus, the LBV nature of SN 2009ip and U2773-OT may provide a critical link between historical LBV eruptions and the unusual dust-obscured transients SN 2008S and N300-OT. (abridged). Comment: 15 pages, 10 Figures, submitted for publication | |||||||||
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