Principal phases in the evolution of single and binary stars
In recent years, the ever growing quantity of data obtained with ground-based instruments and from satellites has led to a greater need for more sophisticated theoretical tools for their interpretation. If until ten years ago the field of theoretical stellar evolution was mainly applied to optical and near-infrared data, in recent years the area of application has widened significantly. Observations now extend to the mid and far-infrared, sub-millimetre and millimetre, so as to permit, in particular, the study of the advanced stages of stellar evolution, often hidden within circumstellar envelopes. Another extension has been made towards X-ray and gamma-ray wavelengths for the understanding of certain interesting phenomena in interacting binary systems.
Two important areas of research are the study of pulsating variables as tracers of the properties of the stellar population and the study of stellar interiors using their pulsations (asteroseismology). The first includes the use of pulsating variables both as primary calibrators for the astronomical distance scale and as indicators for the structure and formation mechanisms of galaxies; the second allows the derivation of intrinsic stellar parameters (mass, luminosity, effective temperature and chemical composition) and above all, the age.
The national scientific community has a well established tradition in the area of theoretical stellar evolution modeling, as well as in the application of its results in various fields of modern astrophysics.
The level of excellence reached over the last decades at an international level, testified by the extraordinary rate of publications and citations, has allowed significant advances in the understanding of stellar evolution, in related fields (such as low energy nuclear physics) and in other fields where the results are applied. The expertise acquired has allowed our community to confront important problems, ranging from the contribution of massive stars to the chemical evolution of galaxies, to the production of compact objects of various kinds.
It is also important to underline that the expertise of the Italian stellar community is absolutely unique, insofar as it allows a homogeneous approach to the study of any aspect of the evolution of a star. This expertise, in fact, goes from stellar nucleosynthesis, the study of the nuclear reactions which take place within a star and produce the nuclei of the chemical elements, to the study of the various evolutionary phases that lead to the formation of white dwarfs, neutron stars and supernovae. The knowledge gained from the CoRoT (Convection, Rotation and planetary Transits) satellite has led to the development of models of stellar interiors that deal in particular with stars that pass through the instability strip and red giants (size of the stellar nucleus, extension of overshoot, rotation profile, age, etc...).
From an instrumental point of view, the Italian stellar community has made a significant contribution to the development of the most modern instruments in the X-ray, optical and near infrared (XSHOOTER - an instrument on ESO's VLT). From an observational point of view, our community takes advantage of the combination of data from very different instruments, from X-ray satellites to very high resolution spectropolarimetry and Very Long Baseline Interferometry (VLBI).
In the coming years, we expect new results from instruments both on the ground and on satellites (such as the aforementioned Herschel and ALMA). In particular, much is expected from the space mission, Global Astrometric Interferometer for Astrophysics (GAIA), that will be launched in 2012.
