Supernova 1954J (Variable 12) in NGC 2403 Unmasked

Abstract

We have confirmed that the precursor star of the unusual supernova 1954J(also known as Variable 12) in NGC 2403 survived what appears to havebeen a superoutburst, similar to the 1843 Great Eruption of {η}Carinae in the Galaxy. The apparent survivor has changed little inbrightness and color over the last 8 years, and a Keck spectrum revealscharacteristics broadly similar to those of {η} Car. This is furthersuggested by our identification of the actual outburst-surviving star inhigh-resolution images obtained with the Advanced Camera for Surveys onthe Hubble Space Telescope. We reveal this ``supernova impostor'' as ahighly luminous (M^{0}_{V}~-8.0 mag), very massive(M_{initial}{\gt}~25 M_{solar}) eruptive star, nowsurrounded by a dusty (A_{V}~4 mag) nebula, similar to {η}Car's famous Homunculus.Based in part on observations with the NASA/ESA Hubble Space Telescope,obtained at the Space Telescope Science Institute (STScI), which isoperated by AURA, Inc., under NASA contract NAS5-26555.