Limb-darkening and radii of non-Mira M giant models

Monochromatic limb-darkening and monochromatic radii predicted by the non-Mira M giant models of Bessell et al. (1989a, 1991) with 3500 K ≥ Teff ≥ 2500 K were computed for selected typical bandpasses used in interferometric and lunar occultation work. Problems of defining and measuring radii of extended-photosphere stars and the relationship between different assumptions on limb-darkening and ’measured’ radii are discussed. Fits of simple uniform disk (UD), fully darkened disk (FDD) and Gaussian limb-darkening curves to the visibilities predicted by the non-Mira M giant models were performed. These fits show that the FDD curve is often a surprisingly good approximation to the model-predicted limb-darkening shape.