LIMB-DARKENING AND RADII OF M-TYPE MIRA MODELS

Monochromatic limb-darkening and monochromatic radii predicted by the M-type Mira models of Bessell et al. (1996) and by new models describe d in Sect. 2 were computed for selected typical bandpasses used in int erferometric and lunar occultation work. The new self-excited pulsatio n model series have periods and luminosities similar to o Ceti and R L eonis and comprise both fundamental (1 M., 1.2 M.) and first overtone (2 M.) pulsators. Fundamental problems of defining and measuring radii of Mira variables caused by the large extension of their atmospheres are discussed. Effective temperatures defined in terms of Rosseland an d continuum radii are generally well determinable with an inherent ina ccuracy of a few percent, but special problems occur for very cool mod els or at phases when models are very cool, below about 2500 K. Fits o f simple uniform disk (UD), fully darkened disk (FDD) and Gauss-shaped limb-darkening curves to the model-predicted visibilities were perfor med and tabulated for a set of 26 x 12 model-filter-combinations cover ing a large variety of typical brightness distributions. These fits sh ow that either the FDD or the Gauss curve is often a good or even exce llent approximation. Limb-darkening curves for specific bandpasses of observational programs can be provided upon request.