Determination of stellar ages and star formation histories - a Bayesian approach With an application to nearby F and G stars

In order to understand the formation and evolution of the Galaxy it is imperative to know when different components formed. This means at the most basic level that we need to know the ages of stars. The present work demonstrates the many problems inherent in determining the ages of stars through comparison with stellar evolutionary models. Furthermore, solutions to some of these problems are presented. This thesis consists of two parts. The first part gives a brief background and explanation of the methods used and the problems encountered. It concludes with a summary of the three research papers that constitute the second part of the thesis. Paper I is a presentation of a catalogue of metallicities, rotational velocities, ages, kinematics, and galactic orbits for more than 14 000 nearby F and G stars. The catalogue is the result of an extensive collaboration involving several institutes, where the main contribution from the present author has been the determination of the ages of the stars. This is described in more detail in Paper II, which presents a new, general and robust way to estimate stellar ages and to quantify their uncertainties. Paper III presents a novel approach to the inverse problem of determining the statistical distribution of ages in stellar samples, or more generally their star formation histories