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A few particles of presolar Al2O3 grains with sizes above 0.5 mum arebelieved to have been produced in the ejecta of core-collapse supernovae (SNe).In order to clarify the formation condition of such large Al2O3 grains, weinvestigate the condensation of Al2O3 grains for wide ranges of the gas densityand cooling rate. We first show that the average radius and condensationefficiency of newly formed Al2O3 grains are successfully described by anon-dimensional quantity "Lambda_on" defined as the ratio of the timescale withwhich the supersaturation ratio increases to the collision timescale ofreactant gas species at dust formation. Then, we find that the formation ofsubmicron-sized Al2O3 grains requires at least ten times higher gas densitiesthan those presented by one-dimensional SN models. This indicates that presolarAl2O3 grains identified as a SN origin might be formed in dense gas clumps,allowing us to propose that the measured sizes of presolar grains can be apowerful tool to constrain the physical conditions in which they formed. Wealso briefly discuss the survival of newly formed Al2O3 grains against thedestruction in the shocked gas within the SN remnants.

Probing the Physical Conditions of Supernova Ejecta with the Measured Sizes of Presolar Al2O3 Grains