Halo and thick-disc giants Li and rotation

Because stars presenting IR excesses are distributed across the majority of metallicity values, we suggest this mechanism is at work throughout an important part of the evolutionary history of the Galaxy. Based on these IR excesses, we identified three Li thresholds: ~1.5dex for RGB stars, ~0.5dex for HB stars, and ~-0.5dex for AGB stars, thereby establishing a new criterion to characterise Li-rich giants in the halo and thick disc.

We carried out a first extensive study of stellar rotations in metal-poor giant stars, revealing the following results: (a) a plateau appears for velocities greater than 40km/s extending up to near 90km/s, with Li abundances ranging from 1.02 to 1.82dex; (b) among Li-rich giant stars with vsini>40km/s, a clear trend toward increasing rotation is observed up to near 90 km/s as metallicities decrease from -1.0 to -2.5; (c) the presence of RGB and HB Li-rich giant stars with rotations up to 90 km/s suggests that internal stellar models must account for extended ^3He reservoir lifetimes as a source of ^7^Li considering these velocities.

The velocity around 40km/s appears to be a new critical value that merits further investigation.