A Method for Determining the Star Formation History of a Mixed Stellar Population

The standard technique for measurement of random uncertainties of star formation histories (SFHs) is the bootstrap Monte Carlo, in which the color-magnitude diagram (CMD) is repeatedly resampled. The variation in SFHs measured from the resampled CMDs is assumed to represent the random uncertainty in the SFH measured from the original data. However, this technique systematically and significantly underestimates the uncertainties for times in which the measured star formation r...

The ongoing surveys of galaxies and those for the next generation of telescopes will demand the execution of high-CPU consuming machine codes for recovering detailed star formation histories (SFHs) and hence age-metallicity relationships (AMRs). We present here an expeditive method which provides quick-look AMRs on the basis of representative ages and metallicities obtained from colour-magnitude diagram (CMD) analyses. We have tested its perfomance by generating synthetic CMD...

Aims. We present here a new theoretical approach to population synthesis. The aim is to predict colour magnitude diagrams (CMDs) for huge numbers of stars. With this method we generate synthetic CMDs for N-body simulations of galaxies. Sophisticated hydrodynamic N-body models of galaxies require equal quality simulations of the photometric properties of their stellar content. The only prerequisite for the method to work is very little information on the star formation and che...

The Bar is the most productive region of the Small Magellanic Cloud in terms of star formation but also the least studied one. In this paper we investigate the star formation history of two fields located in the SW and in the NE portion of the Bar using two independent and well tested procedures applied to the color-magnitude diagrams of their stellar populations resolved by means of deep HST photometry. We find that the Bar experienced a negligible star formation activity in...

We present the spatially-resolved star formation and chemical enrichment history of the Small Magellanic Cloud (SMC) across the entire central $4-degree x 4.5-degree area of the main body, based on UBVI photometry from our Magellanic Clouds Photometric Survey. We find that 1) approximately 50% of the stars that ever formed in the SMC formed prior to 8.4 Gyr ago (z >1.2 for WMAP cosmology), 2) the SMC formed relatively few stars between 8.4 and 3 Gyr ago, 3) there was a rise i...

The exploitation of the power and the spatial resolution of HST and new generation ground-based telescopes allows to measure with good precision the individual stars of galaxies in and beyond the Local Group. This leads to very successful studies of the star formation histories of galaxies of different morphological types. Our current knowledge of the star formation history of galaxies within 10-20 Mpc, as derived from the colour-magnitude diagrams of their resolved stellar p...

Color-Magnitude Diagrams (CMDs) are plots that compare the magnitudes (luminosities) of stars in different wavelengths of light (colors). High nonlinear correlations among the mass, color, and surface temperature of newly formed stars induce a long narrow curved point cloud in a CMD known as the main sequence. Aging stars form new CMD groups of red giants and white dwarfs. The physical processes that govern this evolution can be described with mathematical models and explored...

We present our new, fully-automated method to detect and measure the ages of star clusters in nearby galaxies, where individual stars can be resolved. The method relies purely on statistical analysis of observations and Monte-Carlo simulations to define stellar overdensities in the data. It decontaminates the cluster color-magnitude diagrams and, using a revised version of the Bayesian isochrone fitting code of Ramirez-Siordia et al., estimates the ages of the clusters. Compa...

We present V- and I-equivalent HST/WFPC2 stellar photometry of an area in the Large Magellanic Cloud (LMC), located on the western edge of the bar of the galaxy, which accounts for the general background field of its inner disk. The WFPC2 observations reach magnitudes as faint as V=25 mag, and the large sample of more than 80,000 stars allows us to determine in detail the Present-Day Mass Function (PDMF) of the detected main-sequence stars, which is identical to the Initial M...

We describe the approach adopted by our group to derive the star formation history (SFH) of the chosen LMC field, as part of the experiment to compare the predictions obtained by different groups with the synthetic Colour-Magnitude diagram method. We point out what are the evolutionary characteristics of the observed stellar populations, and present the SFH scenario which appears to better account for them. We emphasize the importance of adopting a {\it critical} approach whe...