The Lithium Abundance and Mass Loss Rate in Galactic Super-Li-Rich Carbon and S Stars

Abstract

The super-Li-rich (SLR) stars are rare AGB stars containing enhanced Li/H ≈ 2000 times the ISM Li/H. In order to determine if mass loss from SLR stars is a significant source of ISM Li, we measured their Li/H and the mass loss rate. From the weak Li I 8126 Â line in 2/4 SLR C stars and 6/8 SLR S stars we obtained Li/H = (0.2 — 5) x 10—6 for SLR C stars and Li/H = (0.2 — 5) x 10—7 for the SLR S stars. We determined dM/dt from the expansion velocity and line profiles of the circumstellar CO. The dM/dt = 1.3 × 10—5M⊙/yr, 2.6 × 10—7M⊙/yr, and 2.6 × 10—8M⊙/yr for the C stars IY Hya, T Ara, and WZ Cas; and average dM/dt = 5.5 × 10—7M⊙/yr for the S stars. Thus mass loss from SLR stars is a significant source of Galactic Li.