A Tale of Two Impostors: SN2002kg and SN1954J in NGC 2403

TL;DR

This paper investigates two supernova impostors in NGC 2403, analyzing their spectral and photometric data to understand their nature, progenitors, and eruption mechanisms, revealing details about their stellar evolution and circumstellar environments.

Contribution

It provides new observational insights into the nature and progenitors of SN 1954J and SN 2002kg, including spectral analysis and evolutionary status, enhancing understanding of supernova impostors.

Findings

SN 1954J survivor is a hot supergiant with T ~ 20000 K and dense wind

SN 2002kg (V37) is a luminous LBV/S Dor variable with an initial mass of 60-80 Msun

V37's eruption was due to enhanced mass loss and wind formation

Abstract

We describe new results on two supernova impostors in NGC 2403, SN 1954J(V12) and SN 2002kg(V37). For the famous object SN 1954J we combine four critical observations: its current SED, its Halpha emission line profile, the Ca II triplet in absorption in its red spectrum, and the brightness compared to its pre-event state. Together these strongly suggest that the survivor is now a hot supergiant with T ~ 20000 K, a dense wind, substantial circumstellar extinction, and a G-type supergiant companion. The hot star progenitor of V12's giant eruption was likely in the post-red supergiant stage and had already shed a lot of mass. V37 is a classical LBV/S Dor variable. Our photometry and spectra observed during and after its eruption show that its outburst was an apparent transit on the HR Diagram due to enhanced mass loss and the formation of a cooler, dense wind. V37 is an evolved hot supergiant at ~10^6 Lsun with a probable initial mass of 60 -80 Msun.