Discovery of Precursor Luminous Blue Variable Outbursts in Two Recent Optical Transients: The Fitfully Variable Missing Links UGC 2773-OT and SN 2009ip

We present progenitor-star detections, light curves, and optical spectra of supernova (SN) 2009ip and the 2009 optical transient in UGC 2773 (U2773-OT), which were not genuine SNe. Precursor variability in the decade before outburst indicates that both of the progenitor stars were luminous blue vari...

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Bibliographic Details
Published in:The Astronomical journal 2010-04, Vol.139 (4), p.1451-1451
Main Authors: Smith, Nathan, Miller, Adam, Li, Weidong, Filippenko, Alexei V, Silverman, Jeffrey M, Howard, Andrew W, Nugent, Peter, Marcy, Geoffrey W, Bloom, Joshua S, Ghez, Andrea M, Lu, Jessica, Yelda, Sylvana, Bernstein, Rebecca A, Colucci, Janet E
Format: Article
Language:English
Subjects:
Links
Outbursts
Precursors
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Summary:We present progenitor-star detections, light curves, and optical spectra of supernova (SN) 2009ip and the 2009 optical transient in UGC 2773 (U2773-OT), which were not genuine SNe. Precursor variability in the decade before outburst indicates that both of the 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 Delta *h Carinae and SN 1954J (V12 in NGC 2403), with intermediate progenitor luminosities. Hubble Space Telescope detections a decade before discovery indicate that the SN 2009ip and U2773-OT progenitors were supergiants with likely initial masses of 50-80 M and 20 M , respectively. Both outbursts had spectra befitting known LBVs, although in different physical states. SN 2009ip exhibited a hot LBV spectrum with characteristic speeds of 550 km s--1, plus evidence for faster material up to 5000 km s--1, resembling the slow Homunculus and fast blast wave of Delta *h Carinae. In contrast, U2773-OT shows a forest of narrow absorption and emission lines comparable to that of S Dor in its cool state, plus [Ca II] emission and an infrared excess indicative of dust, similar to SN 2008S and the 2008 optical transient in NGC 300 (N300-OT). The [Ca II] emission is probably tied to a dusty pre-outburst environment, and is not a distinguishing property of the outburst mechanism. The LBV nature of SN 2009ip and U2773-OT may provide a critical link between historical LBV eruptions, while U2773-OT may provide a link between LBVs and the unusual dust-obscured transients SN 2008S and N300-OT. Future searches will uncover more examples of precursor LBV variability of this kind, providing key clues that may help unravel the instability driving LBV eruptions in massive stars.
ISSN:1538-3881
0004-6256
1538-3881
DOI:10.1088/0004-6256/139/4/1451