Exact mechanism producing the Li-dip remains unknown

Identify the exact physical mechanism that moderates transport processes and inhibits surface lithium depletion in stars cooler than the Li-dip (effective temperatures approximately 6400–6850 K), thereby producing the Li-dip, distinguishing among proposed explanations such as internal gravity waves, atomic diffusion, rotationally induced mixing, and mass loss.

Background

The Li-dip is a well-known depletion of lithium in a narrow effective temperature range near the main-sequence turn-off. The authors map lithium equivalent widths across the HR diagram and clearly delineate the Li-dip, including signs of its evolutionary extension into the subgiant branch.

They attribute the phenomenon to moderation of material transport that normally leads to lithium depletion. However, despite several proposed mechanisms in the literature (internal gravity waves, diffusion, rotationally induced mixing, mass loss), the precise cause of this moderation is still unknown, making the determination of the dominant process an explicit open question.