Boron as a Probe of the Formation of the Galactic Halo, and of Primordial Nucleosynthesis; CYCLE4 Medium

Details Boron as a Probe of the Formation of the Galactic Halo, and of Primordial Nucleosynthesis; CYCLE4 Medium Boron as a Probe of the Formation of the Galactic Halo, and of Primordial Nucleosynthesis; CYCLE4 Medium

Jul 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994hst..prop.5382d&link_type=abstract

HST Proposal ID #5382

Mathematics

Logic

Hst Proposal Id #5382 Cool Stars Evolution/Cosmology

Scientific paper

We propose to observe boron in 3 halo stars of extremely low metallicity ([Fe/H] = -3.1 to -3.5) and combine this data with our ground-based measurements of Be and Li. The evolution of Li, Be, and B has now been shown to be a powerful descriminant between different models of the chemical and dynamical evolution of the galaxy, and must be added to the evolution of [Fe/H] and [O/H] as the critical test of such models. Light element production depends on the intensity and shape of the cosmic ray spectrum, which in turn depends on the supernova rate and thus the star formation rate. It also depends on the rise of the (progenitor) CNO abundances, and the decline of the gas mass fraction, which is affected by rates of infall of fresh (unprocessed) material and outflow, e.g. by supernova heating. The greater efficiency of the post-COSTAR HST will allow us to probe more metal-poor stars than previously observed, so that we can study the earliest phases of formation of the halo. Already the first HST observations of B in halo stars CANNOT BE MATCHED by existing models of galactic chemical evolution. -- In addition, the search for primordial B and Be in the most metal-poor stars allows discriminating between standard and inhomogeneous big bang nucleosynthesis models. Pushing the search for a "plateau" in B and Be (similar to the plateau which demonstrates the cosmological origin of Li) to more metal-poor stars constrains the possiblities of nonstandard models.

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