The formation of lithium lines in the atmospheres of super Li-rich AGB stars

The formation of lithium lines in the: atmosphere of C-rich giants is discu ssed. LTE and NLTE approximations are used to model lithium lines in the sp ectra of super Li-rich AGE stars. The system of equations of the statistica l balance of neutral ii in plane-parallel model atmospheres is solved for a 20-level atom model. JOLA and line-by-line models of molecular absorption are used to compute synthetic spectra as well as the opacity in the frequen cies of bound-bound and bound-free transitions of the lithium lines. Curves of growth and synthetic spectra are computed in LTE and NLTE for several m odel atmospheres of different T-eff and C/O ratios for four lithium absorpt ions, namely: the lambda 4603, lambda 6104, lambda 6708 and lambda 8126 Ang strom ii I lines. The sensitivity of NLTE effects on T-eff and the C/O rati o is discussed. We found that NLTE mainly affects the resonance line double t (lambda 6708) while the impact of NLTE effects on the lithium subordinate lines, formed in the inner regions of C-rich giant atmospheres, is rather weak. Therefore the use of these lines is recommended for ii determination in AGE stars. However, in no case can we properly account for the formation of ii lines in AGE stars until sphericity, velocity stratifications, dust, chromospheres and other related phenomena, which are in fact present in AG E star atmospheres, are considered. Our results are used to derive ii abund ances in three super-Li rich C-stars taking into account NLTE effects. Fina lly, the net ii yield from this class of stars into the interstellar medium is reconsidered.