AAS 203rd Meeting, January 2004
Session 7 Star Formation
Poster, Monday, January 5, 2004, 9:20am-6:30pm, Grand Hall

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[7.01] An Interstellar Origin for the Beryllium 10 in CAIs and Implications for our Solar System's Star Formation Environment

S. J. Desch (Arizona State University), H. C. Connolly, Jr (Kingsborough College, CUNY), G. Srinivasan (University of Toronto)

Beryllium 10 is a short-lived radionuclide (1.5 Myr half-life) that was incorporated live, at the birth of the solar system, into calcium-aluminum-rich inclusions (CAIs) in meteorites. The initial ratio of 10Be/9Be was 1 x 10-3. Beryllium 10 differs from other radionuclides in meteorites (e.g., aluminum 26) in that it must be formed by spallation reactions and not by nucleosynthesis, e.g. a supernova. Previous analyses also ruled out galactic cosmic rays (GCRs) as the source of the beryllium 10 and concluded that spallation reactions must have occurred in the solar nebula, due to energetic particles from the early Sun. We re-examine this conclusion by calculating the contributions from GCRs, both from spallation reactions and from trapping of 10Be GCRs as they lose energy passing through the molecular cloud core from which our solar system formed. To do so, we constrain the flux and composition of GCRs 4.5 Gyr ago and use numerical magnetohydrodynamic simulations of star formation to calculate the time-varying rate of entry of GCRs into a molecular cloud core. We find that spallation reactions by GCRs can account for 20% of the meteoritic 10Be in CAIs, and trapping of 10Be GCRs can account for 80%. Our uncertainties are about a factor of three. We conclude that contributions to 10Be from GCRs cannot be ruled out, and are capable of explaining all the 10Be in CAIs. These findings, together with the recent discovery that meteorites contained live iron 60 when they formed, strongly imply that our solar system formed in a high-mass-star forming region, near a supernova.

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Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.