AAS 207th Meeting, 8-12 January 2006
Session 42 Element and Stellar Evolution
Oral, Monday, 10:00-11:30am, January 9, 2006, Wilson A/B

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[42.01] Beryllium in Ultra-Li-Deficient Halo Stars

A. M. Boesgaard (IfA, U. Hawaii)

The vast majority of low-metal halo dwarfs show a similar amount of Li; this has been attributed to the primordial Li that was produced in the Big Bang. However, there are nine known halo stars with T > 5900 K and [Fe/H] < -1.0 that are ultra-Li-deficient. We have looked for the Be II resonance lines in the near ultraviolet in several of these stars with high resolution,high signal-to-noise spectra from Keck 1 with HIRES and Subaru with HDS. There are at least two potential causes for the Li-deficiencies: 1) mass-transfer in a pre-blue straggler or 2) extra rotationally-induced mixing in a star that was initially a very rapid rotator. Most of the stars have very low upper limits on the Be abundance which favors the blue-straggler hypothesis. Two stars seem to have small, but detectable, amounts of Be. The comparison with Be spectra of Li-normal, Be-normal stars shows severe Be depletion in all cases. One consequence of this study relates to the interpretation of the ultra-Li-deficient, metal-poor stars in the context of the value for primordial Li. The Be deficiencies indicate that the Li-deficiencies result from mass-transfer events and not from Li depletion from internal mixing processes. Such processes might affect Li in all of the Li plateau stars (but to a smaller extent) which would have implied a lower primordial Li than that inferred by excluding the ultra-Li-deficient stars as outliers.

This work has been supported by grants from the National Science Foundation.

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