A Rapidly Fading Star as a Type II Obscuring Intermediate Luminosity Optical Transient (ILOT) in a Triple-star System

Abstract

We propose a triple-star scenario where the merger of two pre-main-sequence low-mass stars, ≲0.5 M ⊙, ejects a dusty equatorial outflow that obscures and temporarily causes the disappearance of a massive star, ≳8 M ⊙. The merger of the low-mass inner binary powers a faint outburst, i.e., a faint intermediate luminosity optical transient (ILOT), but its main effect that can last for decades is to (almost) disappear the luminous massive star of the triple system. The typical orbital period of the triple system is about 1 yr. The merger process proceeds as the more-massive star of the two low-mass pre-main-sequence stars starts to transfer mass to the least-massive star in the triple system and as a result of that expands. This type II obscuring ILOT scenario in a triple-star system might account for the fading, rebrightening, and then refading of the massive post-main-sequence star M101-OC1. It might recover in about 20–100 yr. Our study strengthens the claim that there are alternative scenarios to account for the (almost) disappearing of massive stars, removing the need for failed supernovae. In these scenarios the disappearing is temporary, lasting from months to decades, and therefore at a later time the massive star explodes as a core collapse supernova, even if it forms a black hole.