Supernova 1954J (Variable 12) in NGC 2403 Unmasked

We have confirmed that the precursor star of the unusual supernova 1954J (also known as Variable 12) in NGC 2403 survived what appears to have been a superoutburst, similar to the 1843 Great Eruption of η Carinae in the Galaxy. The apparent survivor has changed little in brightness and color over the last 8 years, and a Keck spectrum reveals characteristics broadly similar to those of η Car. This is further suggested by our identification of the actual outburst-surviving star in high-resolution images obtained with the Advanced Camera for Surveys on the Hubble Space Telescope. We reveal this ``supernova impostor'' as a highly luminous (M⁰_V~-8.0 mag), very massive (M_initial>~25 M_solar) eruptive star, now surrounded 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 is operated by AURA, Inc., under NASA contract NAS5-26555.