The plausible sources of 26Al in the early solar system: A massive star or the X-wind irradiation scenario?

Abstract

A quantitative analysis is presented for the irradiation contributions of the short-lived nuclides, specifically 26Al, by the X-wind scenario in the early solar system. The analysis is based on the comprehensive numerical simulations of the scenario that involves thermal processing of protoCAIs during the decades long X-wind cycle. It would be difficult to explain the canonical value of 26Al/27Al in Ca-Al-rich inclusions on the basis of its inferred irradiation yields. Hence, the bulk inventory of 26Al in the early solar system was not produced by the X-wind scenario. We suggest the predominant occurrence of gradual flares compared to impulsive flares in the early solar system as in the case of the modern solar flares. One tenth of the bulk 26Al was only produced by irradiation in case the entire solar inventory of 10Be was produced by local irradiation. The bulk 26Al inventory along with 60Fe was probably synthesized by a massive star. We present a qualitative model of the astrophysical settings for the formation of the solar system on the basis of a survey of the presently active star forming regions. We hypothesize that the formation of the solar system could have occurred almost contemporaneously with the formation of the massive star within a single stellar cluster. As the massive star eventually exploded as supernova Ib/c subsequent to Wolf-Rayet stages, the short-lived nuclides were probably injected into the solar proto-planetary disc. The dynamically evolving stellar cluster eventually dispersed within the initial ~10 million years prior to the major planetary formation episodes.