Luminous Blue Variable Star - Supernovae and Imposters

Supernovae and Imposters

Luminous blue variable stars can undergo "giant outbursts" with dramatically increased mass loss and luminosity. Eta Carinae is the prototypical example, with P Cygni showing one or more similar outbursts 300-400 years ago, but dozens have now been catalogued in external galaxies. Many of these were initially classified as supernovae but since re-examined because of unusual features. The nature of the outbursts and of the progenitor stars seems to be highly variable, with the outbursts most likely having several different causes. The historical Eta Carinae and P Cygni outbursts, and several seen more recently in external galaxies, have lasted years or decades while some of the supernova imposter events have declined to normal brightness within months. Well-studied examples are:

• SN 1954J
• SN 1961V
• SN 1997bs
• SN 2008S

Early models of stellar evolution had predicted that while the high mass stars that produce LBVs would often or always end their lives as supernovae, the supernova explosion would not occur at the LBV stage. Prompted by the progenitor of SN 1987A being a blue supergiant, and most likely an LBV, several subsequent supernovae have been associated with LBV progenitors. The progenitor of SN 2005gl has been shown to be an LBV apparently in outburst only a few years earlier, while SN 2009ip was first shown to be a giant outburst of an LBV star, followed by two more in quick succession, and finally a true supernova.