Structure and evolution of circumstellar disks, a Spitzer view

This dissertation is the sum of five studies of the structure and evolution of circumstellar disks, the birthplace of planets. These studies are all based on Infrared data from the Spitzer Space Telescope, and taken together trace the evolution of disks from the optically thick primordial stage to the optically thin debris disk stage. The five projects included in this dissertation are diverse but they are all interconnected and have a common underlying motivation: to impose observational constraints on different aspects of planet formation theories. In the first project, we study the near and mid-IR (1.2-24 [mu]m) emission of Classical T Tauri Star (CTTS), which are low-mass pre-main sequence (PMS) stars that show clear evidence for accretion. We discuss the implications of our results on the structure of their inner disks and their estimated ages. In the second project, we study the incidence as a function of age of disks around weak-line T Tauri stars (low-mass PMS stars that are mostly coeval with CTTS but that do not show clear evidence for accretion) and explore the structure of these disks. We estimate the dissipation timescale of the planet-forming region of primordial disks and discuss the implications for planet formation theories. The third and fourth projects deal with the evolution of angular momentum of PMS stars. We search for observational evidence for the connection between stellar rotation and the presence of a disk predicted by the current disk-braking paradigm, according to which the rotational evolution of PMS stars is regulated through magnetic interactions between the stellar magnetosphere and the inner disk. The last project deals with debris disks, which are second-generation disks where the dust is continuously replenished by collisions between planetesimals. We search for debris disks in the far-IR (24-160 [mu]m) around a sample of Hyades Cluster members. We discuss the implications of our results on the evolution of debris disks and on the Late Heavy Bombardment in the Solar System.