Al-26: Origin, Variation, And Implications

Details Al-26: Origin, Variation, And Implications Al-26: Origin, Variation, And Implications

Sep 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008dps....40.5801g&link_type=abstract

American Astronomical Society, DPS meeting #40, #58.01; Bulletin of the American Astronomical Society, Vol. 40, p.502

Astronomy and Astrophysics

Astronomy

Scientific paper

We evaluated four scenarios for the incorporation of the short-lived radionuclide Al-26 from massive stars into circumstellar solids (represented in the Solar System by refractory inclusion in primitive meteorites). Injection into a disk during Class II protostellar evolution is highly unlikely (< 1%) to produce the canonical early Solar System abundance. Models of scenarios in which massive stars pollute the remaining gas of the embedded cluster or a host giant molecular cloud with radionuclides, and later-forming stars, can generate abundances closer to the Solar System value if the time delay between star formation and solid condensation is a million years or less. Inclusion of Bondi-Hoyle accretion increases the average abundance of Al-26 in disks but does not affect the estimated frequency of systems with an Al-26 abundance like the early Solar System. Our models predict an initial abundance of exogenous Al-26 in planetary systems from 0 to Al-26/Al-27 1E-4. The majority receive no Al-26 from massive stars because they formed before the most massive stars evolved away from the main sequence. A major uncertainty in all the models is the formation and transport of Al-26 as Al-bearing dust grains in winds or SN ejecta. Even if the primary mechanism of Al-26 production is, instead, irradiation by energetic particles from the central star, this source will also vary between stars by about two orders of magnitude. Planetesimals in disks with different abundances of Al-26 will experience different thermal histories. If the position of the boundary between dehydrated and hydrated bodies, located at 2.5 AU in the Main Asteroid Belt, is set by the relative rates of accretion and the decay of Al-26, the location of this "waterline” will depend on the initial abundance of Al-26 and affect the amount of water accreted by terrestrial planets in the habitable zone.

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