Li-rich stars and their 6Li/7Li isotope ratio.

Li-rich stars and their 6Li/7Li isotope ratio. Is it indeed possible to detect 6Li in stellar atmospheres?

Stellar lithium abundances together with the 6Li/7Li isotope ratios offer valuable observational constraints on the origin and evolution of lithium - a chemical element with the most complicated formation history. We introduce and validate a novel approach for lithium abundance and isotope ratio determination. In stars with well-determined parameters and high-quality spectra, we analyse the Li I subordinate line at 6103 A and the resonance line Li I 6707 A, considering deviations from the local thermodynamic equilibrium (non-LTE effects). The Li I 6103 A line is weak and immune to the adopted isotope ratio, we use this line for lithium abundance determination. In contrast, the resonance line Li I 6707 A is sensitive to the assumed isotope ratio, and different abundances are obtained when assuming different 6Li/7Li. Additionally, we account for 3D effects using the literature data. We analyse Li-rich stars with diverse atmospheric parameters, from turn-off stars to red giants, and determine their Li abundances and 6Li/7Li ratios. In 1D non-LTE, the presence of 6Li remains negligible within a 2-sigma error in our sample stars. However, when accounting for 3D effects, a considerable amount of 6Li is observed, posing a challenging explanation. Expanding our method to stars with distinct chemical compositions, evolutionary stages, activity levels, binarity, etc., makes it a promising tool for providing insight on mechanisms of 6Li and 7Li synthesis. 

Theme(s): New Insights into Star Formation and Evolution, Cool Stars as Stellar Systems