An inversion technique has been developed to recover LTE one-dimensional model photospheres for late-type stars from very high-resolution high signal-to-noise stellar line profiles. It is successfully applied to the Sun using a set of unblended Ti 1, Ca 1, Cr 1 and Fe 1 lines with accurate transition probabilities. Temperature stratification

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We have developed an efficient and accurate set of mostly analytic formulae, that describe the evolution of stars in a wide range of mass and metallicity from the zero-age main sequence to the tip of the AGB. These formulae are based on interpolation between full detailed stellar models. A particular advantage of this kind of algorithm, compared

We present an algorithm for rapid evolution of binary stars. This incorporates single star evolution based on simple fitting formulae that cover a wide range in mass and metallicity. Mass loss, Roche mass transfer and common-envelope evolution are followed with the changes applied to both the primary and secondary where applicable. Due to the large

We present two selected photoionization models of the extragalactic H ii region NGC 2363, and compare them with three sets of observational data. We discuss the effect of adopting different input parameters. We show that the metallicity of NGC 2363 has most probably been underestimated, and that a value of Z ~= .25 Z_odot is in good agreement with