Lithium lines in the spectra of M dwarfs: UX Tau C

The results of numerical modeling of lithium lines in the spectra of M dwar fs are discussed. The behavior of the lithium lines relative to the local p seudocontinuum formed by molecular bands is analyzed as a function of model atmosphere parameters: effective temperature T-eff, gravity log g, and met allicity mu. The molecular opacity was computed using the just overlapping line approximation (JOLA) and "line-by-line" methods. The pseudo-equivalent widths of lithium lines depend appreciably on metallicity mu and weakly on T-eff. The lithium abundance in the atmosphere of UX Tau C is redetermined . Previous studies underestimated the lithium abundance in this star as a r esult of the use of insufficiently accurate molecular-line lists. The new l ithium abundance logN (Li) = 3.2 +/- 0.3 was derived by comparing the obser ved profiles of the 670.8 nm resonance doublet lines with profiles calculat ed using the new TiO line list of Plez.(1) The new abundance agrees with th e atmospheric lithium abundances of the other two components in the stellar system, providing further evidence that the three stars in the UX Tau syst em have the same age. A comparison of the observed spectra of UX Tau C near the lithium resonance doublet (665-680 nm) with spectra computed using JOL A and line-by-line methods suggests that the list of Plez is the best curre ntly available. (C) 2000 MAIK "Nauka/Interperiodica".