T Tauri stars: an overview

The review presents the main aspects of the body of knowledge on T Tauri variable stars, which are presumed to be young, gravitationally contracting low-mass stars. The author first reviews their often exotic properties in the different wavelength ranges accessible to modern astronomy and discuss the data's immediate interpretation. He then describes some theoretical results of protostellar evolution computations with the intention of defining a framework for discussing the quantitative models which have been proposed for T Tauri stars. Although a unified picture of the T Tauri phenomenon has yet to emerge, major advances have occurred in the last few years in the study of physical processes potentially relevant to these stars (e.g. the role of magnetic fields in driving stellar winds and stellar activity). He reviews these current models and identifies those properties of the stars which now seem well understood. Lastly, at the risk of being quickly outdated, he goes on to draw some tentative conclusions about the nature of the T Tauri phenomenon.