Disk observations

Abstract

A wide variety of observations suggest that solar mass stars are surrounded by disks of gas and dust for much of their pre-main sequence lifetimes and even beyond. Here, techniques by which the small-scale circumstellar material can be detected are described and evidence for disks is briefly reviewed. Because of the general similarity between the disks around solar-mass stars and the nebula that surrounded the sun as the planets formed, disk properties may have strong bearing on our understanding of solar system evolution. Questions which must be addressed include: How frequently are disks found, and does the fraction vary with environment? What effect do companion stars have? How do disks evolve? Are low infrared fluxes necessarily indicative of disk clearing? Is there evidence of chemical evolution? How long do the disks persist? Are dissipation time-scales different for the gas and dust components? Observations addressing such problems will be summarized and discussed.