Despite both being outbursts of luminous blue variables ( LBVs ) , SN 2009ip and UGC 2773 OT2009-1 have very different progenitors , spectra , circumstellar environments , and possibly physical mechanisms that generated the outbursts .
From pre-eruption HST images , we determine that SN 2009ip and UGC 2773 OT2009-1 have initial masses of \gtrsim 60 and \gtrsim 25 M _ { \sun } , respectively .
Optical spectroscopy shows that at peak SN 2009ip had a 10,000 K photosphere and its spectrum was dominated by narrow H Balmer emission , similar to classical LBV giant outbursts , also known as “ supernova impostors. ” The spectra of UGC 2773 OT2009-1 , which also have narrow H \alpha emission , are dominated by a forest of absorption lines , similar to an F-type supergiant .
Blueshifted absorption lines corresponding to ejecta at a velocity of 2000 – 7000 km s ^ { -1 } are present in later spectra of SN 2009ip — an unprecedented observation for LBV outbursts , indicating that the event was the result of a supersonic explosion , rather than a subsonic outburst .
The velocity of the absorption lines increases between two epochs , suggesting that there were two explosions in rapid succession .
A rapid fading and rebrightening event concurrent with the onset of the high-velocity absorption lines is consistent with the double-explosion model .
A near-infrared excess is present in the spectra and photometry of UGC 2773 OT2009-1 that is consistent with \sim 2100 K dust emission .
We compare the properties of these two events and place them in the context of other known massive star outbursts such as \eta Car , NGC 300 OT2008-1 , and SN 2008S .
This qualitative analysis suggests that massive star outbursts have many physical differences which can manifest as the different observables seen in these two interesting objects .