Protostars, Circumstellar Disks, and the Environments of Protoplanetary Evolution

M. McCaughrean
Max Planck Institut, Heidelberg, Germany

We will present a general overview of protostellar evolution in the context of planet formation, with a review of the "standard model" for star formation, which considers a single star forming in isolation. An important phase involves accretion through a circumstellar disk, particularly because such disks are held to be the progenitors of planetary systems. Since present technology allows us to discover and study disks in more detail than is yet possible for planets themselves, disks around young stars have much to tell us about the process of planet formation.

We will begin by discussing the present state of observations of disks around young stars in the nearby Taurus-Auriga and Ophiuchus dark clouds. In particular, we will present the evidence that over 50% of all young stars in these regions are surrounded by circumstellar disks massive enough to form planetary systems, implying that such systems should be common in the galaxy.

We will then examine recent ground- and space-based observations of young stars and circumstellar disks in more distant regions of massive star formation. H II regions such as M42 (the Orion Nebula) and M16 (the Eagle Nebula) contain dense clusters of young stars, and are more typical of the origin of the bulk of galactic field stars. We shall discuss how the evolution of circumstellar disks may be radically affected by their environments, by the ionization and winds of nearby massive stars, by catastrophic events such as supernovae, and in interactions with other cluster stars. We will present the evidence that, despite these effects, the prospects for planet formation around stars in such environments appear to remain good.

Finally, we will describe the future progress that is likely with the next generation of ground- and space-based instruments in studying these "Rosetta Stones" for planet formation.