NONLOCAL THERMODYNAMIC-EQUILIBRIUM EFFECTS OF TI-I IN M-DWARFS AND GIANTS

We present detailed NLTE Ti I calculations in model atmospheres of coo l dwarf and giant stars. A fully self-consistent NLTE treatment for a Ti I model atom with 395 levels and 5279 primary bound-bound transitio ns is included, and we discuss the implication of departures from LTE in this atom for the strengths of Ti I lines and TiO molecular bands i n cool star spectra. We show that in the atmospheric parameter range i nvestigated, LTE is a poor approximation to Ti I line formation, as ex pected from the low collisional rates in cool stars. The secondary eff ects of Ti I overionization on the TiO number density and the TiO mole cular opacities, however, are found to be negligible in the molecular line-forming region for the relatively small parameter range studied i n this paper.