Circumstellar disks are a natural outcome of the star formation process. The gravitational collapse of a rotating molecular cloud core produces a flattened disk of gas and dust that channels mass inwards to build up a central star. The orbital motion of the disk material stores a large fraction of the angular momentum in the system, and plays a critical role regulating the stellar rotation rate for millions of years. Of course, the gas and dust in a disk are also fundamentally important for the planet formation process, serving as the material reservoir that will eventually be used to make planets. By studying the physical properties and evolution of the raw material in disks, we try to better understand the initial conditions that influence the assembly of a planetary system. In many ways this approach is an essential complement to investigations of extrasolar planets and cosmochemistry in our Solar System; we simply approach an understanding of the complicated planet formation process from opposite perspectives in time.
I use observations of circumstellar disks to help infer the physical conditions (densities and temperatures) and structure (sizes and geometry) of their gas and dust content. Although a pan-chromatic approach is important, my work relies heavily on data at radio frequencies. This part of the spectrum is particularly useful for several reasons: (1) no contrast problems - contamination from the star is negligible; (2) high angular resolution - interferometers are crucial for resolving the small angular scales (often < 1") subtended by disks; (3) molecular spectra - low-energy rotational transitions can be used to study chemistry, dynamics, and structure; and (4) optically thin dust emission - the most direct probe of disk masses. The latter is especially significant because the mass distribution of a disk offers unique insights into its evolution and the likelihood of future planet formation.
Profound technological advances in radio telescopes will available in the very near future, with the completion of the ALMA interferometer construction expected in 2012 and the EVLA upgrade by 2011. With the promise of coupling observations with those facilities and infrared data from the Herschel and JWST space missions, the next decade promises to be a revolutionary period in our understanding of the roles disks play in both star and planet formation. Some highlights of the work we are doing with current facilities are available by clicking the tabs at the top of this box. Details can be found in our recent publications.