The Temperature Scale of Metal‐rich M Giants Based on TiO Bands: Population Synthesis in the Near‐Infrared

We have computed a grid of high-resolution synthetic spectra for cool stars (2500< T eff <6000 K) in the wavelength range 6000-10200 Å by employing an updated line list of atomic and molecular lines together with state-of-the-art model atmospheres. As a by-product, by fitting TiO band heads in spectra of well-known M giants, we have derived the electronic oscillator strengths of the TiO γ', δ, , and ϕ systems. The derived oscillator strengths for the γ', , and ϕ systems differ from the laboratory and ab initio values found in the literature, but they are consistent with the model atmospheres and line lists employed, resulting in a good match to the observed spectra of M giants of known parameters. The behavior of TiO bands as a function of the stellar parameters T eff , log g and [Fe/H] is presented, and the use of TiO spectral indices in stellar population studies is discussed.