THE DETECTION AND STUDY OF PREPLANETARY DISKS

A variety of evidence suggests that at least 50% of low-mass stars are surrounded by disks of the gas and dust similar to the nebula that su rrounded the Sun before the formation of the planets. The properties o f these disks may bear strongly on the way in which planetary systems form and evolve. As a result of major instrumental developments over t he last decade, it is now possible to detect and study the circumstell ar environments of very young, solar-type stars in some detail, and to compare the results with theoretical models of the early solar system . For example, millimeter-wave aperture synthesis imaging provides a d irect means of studying in detail the morphology, temperature and dens ity distributions, velocity field and chemical constituents in the out er disks, while high resolution, near infrared spectroscopy probes the inner, warmer parts; the emergence of gaps in the disks, possibly ref lecting the formation of planets, may be reflected in the variation of their dust continuum emission with wavelength. We review progress to date and discuss likely directions for future research.