LITHIUM IN HALO DWARFS: THE UNDOING OF DIFFUSION BY MASS LOSS

摘要

It has been recognized for a decade that stellar models which account for the microscopic diffusion of lithium are not compatible with the nearly uniform lithium abundance, as a function of temperature, found in metal-poor halo dwarfs (the Spite plateau). The recent observations of Thorburn (1994) extend the Spite plateau by about 200 degrees (to higher temperatures) and thus significantly exacerbate the problem. Herein it is shown that microscopic diffusion can be compatible with the lithium observations if mild main-sequence mass loss occurs throughout the evolution of these halo dwarfs. Mass-loss rates of ～ -1 x 10~(-12) solar mass yr~(-1) are required. These models suggest that halo stars have depleted their initial lithium uniformly by a factor of ～1.6 or 0.2 dex. These models should also provide agreement with globular cluster color-magnitude diagrams superior to that of diffusion models without mass loss.