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 < 6000K) in the wavelength range 6000-10200 Angstrom by empl oying an updated line list of atomic and molecular lines together with stat e-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 oscillato r strengths of the TiO gamma', delta, epsilon, and phi systems. The derived oscillator strengths for the gamma' epsilon and phi systems differ from th e laboratory and ab initio values found in the literature, but they are con sistent with the model atmospheres and line lists employed, resulting in a good match to the observed spectra of M giants of known parameters. The beh avior 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 populati on studies is discussed.