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

It has been recognized for a decade that stellar models which account for the microscopic diffusion of lithium are not compatible with the n early uniform lithium abundance, as a function of temperature, found i n metal-poor halo dwarfs (the Spite plateau). The recent observations of Thorburn (1994) extend the Spite plateau by about 200 degrees (to h igher temperatures) and thus significantly exacerbate the problem. Her ein 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 approximately - 1 x 10(-12) M(.) yr-1 are required. These models suggest that halo s tars have depleted their initial lithium uniformly by a factor of appr oximately 1.6 or 0.2 dex. These models should also provide agreement w ith globular cluster color-magnitude diagrams superior to that of diff usion models without mass loss.