STATISTICAL PROPERTIES OF STELLAR POPULATIONS AND SURFACE-BRIGHTNESS FLUCTUATIONS IN GALAXIES

Some relevant concepts dealing with the statistical properties of stellar populations are approached and explored in detail defining the effective stellar contributors N(eff), and the effective luminosity l(eff) of a stellar aggregate. These two quantities strictly relate to the distinctive properties of a stellar population, and basically modulate the intrinsic statistical scatter in a pixel-to-pixel surface photometry of a galaxy (providing that photon scatter and other perturbing effects are excluded). The effective luminosity and number contributors in simple stellar populations have been calculated through a set of 206 models based on Buzzoni's (1989) code for population synthesis, including also the case of composite stellar populations. The results have been applied to the Tonry-Schneider (1988) method on galaxy surface-brightness fluctuations deriving new distances for M 32 and galaxies in the Virgo cluster as well as in the Leo, Fornax, and Eridanus groups observed by Tonry and colleagues. The distance of Virgo is found to be 15.3 Mpc supporting Tonry's (1991) previous estimate. Also the distance of the Galactic globular cluster M 3 has been derived resting on the complete sample of 10000 stars by Buonanno et al. (1986,1988). We obtain a distance modulus (m - M)0 = 15.01 +/- 0.13 in excellent agreement with other current estimates confirming the reliability of the Tonry-Schneider method once accurate theoretical models for population systhesis are considered.