Numerical simulations of the production of extinct short-lived nuclides by magnetic flaring in the early solar system

Abstract

Using the X-ray flare observations of low-mass protostars, we developed numerical simulations of thermal processing and irradiation of protoCAIs in the magnetic reconnection ring within the X-wind formulation. Observed X-ray flare luminosities have been used to model various simulation flare characteristics. Several approximations have been made regarding the thermal evolution that involve condensation, evaporation, and coagulation of protoCAIs. Ensembles of refractory cores with ferromagnesian mantles were evolved for irradiation production of the short lived nuclides 7Be, 10Be, 41Ca, 36Cl, 26Al, and 53Mn. Three distinct grain-size distributions of protoCAIs with refractory cores in the ranges of 32 micrometer-20 mm, 125 micrometer-16 mm, and 500 micrometer-13 mm were thermally evolved for irradiation. The latter two size distributions were found to result in the accumulation of protoCAIs in the reconnection ring during an X-wind cycle, and hence can account for the total inventory of 26Al in the early solar system. The canonical value of ~5 x 10^(-5) for 26Al/27Al can be inferred from the impulsive flare simulations by a suitable choice of simulation parameters. However, in most of the remaining simulations, the irradiation of protoCAIs by superflare(s) with Lx > 10^32 ergs s^(-1) subsequent to their thermal processing in the reconnection ring would be required to explain the experimental abundances of the short-lived nuclides. These superflares have never been reliably observed in young stellar objects. If they are real, they would be extremely rare. The paucity of these superflares could impose stringent constraints on the validity of the X-wind irradiation scenario as the source of the short-lived nuclides.