Surveys of the resolved stellar content of entire galaxies are the natural tool to study fast evolutionary phases of massive stars. Therefore we launched the Magellanic Clouds Massive Stars and Feedback Survey (MCSF) and periodically imaged for 3 years the entire Small and Large Magellanic Cloud in u, B, V, R, I and Hα, [Oiii], [Sii] using the twin telescope RoBoTT at the University Observatory of the Ruhr-University Bochum at Cerro Armazones, Chile. Observations with short exposure times are included to ensure brightest stars not to be saturated, yielding a full coverage in luminosity. With this unique dataset we can study the massive stellar populations up to MB ∼ −10 mag and their feedback. Upon completion a high quality photometric and spatially complete catalog of the Magellanic Clouds will be established which is be comparable (or even beyond) the quality of HST based photometry of nearby galaxies.

We explore the non-standard mixing history of five solar twins to determine as precisely as possible their mass and age. For this, we computed a grid of evolutionary models with non-standard mixing at given metallicities with the Toulouse-Geneva code for a range of stellar masses. We choose the evolutionary model that best fit the low lithium abundances observed in the solar twins. Our best model for each solar twin provides a mass and age solution constrained by their Li content and Teff determination. Li depletion due to the additional mixing in solar-twins is strongly mass dependent. An accurate lithium abundance measurement connected with non-standard models provides a more precise information about the age and mass better than that determined only by classical methods.

We report on the development of a new stellar evolution code, and provide a taste of results, showing its capability to calculate full evolutionary tracks for a wide range of masses and metalicities. The code is fast and efficient, and is capable of following through all evolutionary phases, including core/shell flashes and thermal pulses, without any interruption or intervention. It is meant to be used also in the context of modeling the evolution of dense stellar systems, for performing live calculations for both ‘normal’ ZAMS/PRE-MS models, but mainly for ‘non-canonical’ stellar configurations (i.e. merger-products). We show a few examples of evolutionary calculations for stellar populations I and II, and for masses in the range 0.25–64 M⊙.

A new method to extract information from color-magnitude diagrams (CMDs) is presented. We employ a Richardson-Lucy (RL) algorithm to the analysis of the observational uncertainties. The resulting reconstruction is a cleaned data set with which to perform analyses of the star formation history. For this task, synthetic stellar populations are built and compared with the data CMD. As an application, the star formation rate in the solar vicinity is recovered.

IAC-pop is a code designed to solve the star formation history (SFH) of a complex stellar population system, like a galaxy, from the analysis of the color-magnitude diagram (CMD). It uses a genetic algorithm to minimize a χ2 merit function comparing the stellar distribution of an observed CMD and the stellar distributions of CMDs arising from linear combination of simple synthetic populations. To this purpose, IAC-star is used to compute a single seminal synthetic CMD from which the simple populations and their corresponding CMD stellar distributions are extracted.

In the current version, IAC-pop provides two different estimates of the errors in the SFH. It is offered for free use and can be downloaded from the site www.iac.es/iac-pop.html.

Microturbulence is usually treated in model atmospheres as a free parameter (ξt) that allows to re-establish agreement among abundances derived from different lines. Even if this parameter is a consequence of treating a 3D problem as a 1D one, it seems clear that microturbulence is linked to the velocity field within the atmosphere, and therefore to convection in the external layers. The values of the parameter as determined from observations show a dependence both on effective temperature and on surface gravity. In this paper we study how the microturbulence parameter used in the atmosphere models affects the theoretical color-magnitude diagram (CMD). First, in the Main Sequence (MS) domain due to the dependence of the microturbulence parameter on Teff; and second, in the giant branch (Pre-main sequence and Red Giant Branch) where several photometric indexes show a large variation due to the increase of the microturbulence parameter as the stellar gravity decreases. We predict then a significant change in the CMD, as well as in the color-temperature calibrations, if variations of ξt such as those observationally determined are included in theoretical CMD computations.

Stars in various parts of the HR diagram often have atmospheres in which the departure from the simplest kind of plane-parallel model is largely dominated by a single physical effect. For example, massive stars and giants exhibit symptoms of strong winds and lower Main Sequence stars are very strongly influenced by the presence of deep and energetic envelope convection. Main Sequence A stars, in contrast, appear to display the competing effects of several physical effects of comparable magnitude. The effects which can be detected by observation include large and relatively simple magnetic fields, strong surface convection, pulsation (often in multiple modes), diffusion of specific species under the competing influences of gravity and radiative acceleration, and (more indirectly) internal turbulent mixing, weak winds, and non-thermal heating. This situation makes these stars extremely useful as laboratories to explore and to understand the physics of these various phenomena, and how these effects interact with each other. This review will summarize some of the interconnections that are gradually being understood and emphasize some of the major remaining problems.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html