Galactic Twins of the Nebula Around SN 1987A: Hints that LBVs may be supernova progenitors

Abstract

I discuss outstanding questions about the formation of the ring nebula around SN1987A and some implications of similar ring nebulae around Galactic B supergiants. There are notable obstacles for the formation of SN1987A's bipolar nebula through interacting winds in a transition from a red supergiant to a blue supergiant. Instead, several clues hint that the nebula may have been ejected in an LBV-like event. In addition to the previously known example of Sher25, there are two newly-discovered Galactic analogs of SN1987A's ringed nebula. Of these three Galactic analogs around blue supergiants, two (Sher25 and SBW1) have chemical abundances indicating that they have not been through a red supergiant phase, and the remaining ringed bipolar nebula surrounds a luminous blue variable (HD168625). Although SK-69 202's initial mass of 20 Msun is lower than those atributed to most LBVs, it is not far off, and the low-luminosity end of the LBV phenomenon is not well defined. Furthermore, HD168625's luminosity indicates an initial mass of only 25 Msun, that of SBW1 is consistent with 20 Msun, and there is a B[e] star in the SMC with an initial mass of 20 Msun that experienced an LBV outburst in the 1990s. These similarities may be giving us important clues about Sk-69 202's pre-SN evolution and the formation mechanism of its nebula.