Modeling the Diversity of Protoplanetary Disks

Grant #: NNX14AR91G
Senior Scientist: Uma Gorti

Protoplanetary disks play a central role in star formation and are the birthplaces of planets. Disks are short-lived and survive for a few Myrs before being dispersed, possibly by a combination of viscous accretion and photoevaporation by high energy photons from the central star. Disks evolve along diverse pathways, they may or may not develop gaps or central cavities, may get truncated or expand out to large radii, and lose their mass on timescales that vary widely from source to source. However, disk evolution is mainly probed by dust, which comprises only 1% of the total mass. Gas is the dominant component and is probed by weak emission lines emitted by trace chemical species. Gas disks are also short-lived, but gas evolution is largely unknown. The availability of sufficient gas in planet forming regions for extended time periods is critical to planet formation and dynamics. Studying the gas component of protoplanetary disks is essential to understanding how disks evolve and form planets. 

NASA's Spitzer and Herschel missions have recently detected gas lines from the important, 1-100 AU, planet-forming regions of disks in many star-forming regions, allowing detailed studies of gas disk evolution. The complexity of disk structure and the sensitivity of the observed lines to physical conditions such as the stellar radiation field, and disk density, temperature and chemistry make theoretical models necessary to interpret the observed emission. 

We propose a multiwavelength analysis of gaseous protoplanetary disks by modeling archival Spitzer, ISO and Herschel infrared line emission data using our gas disk thermo-chemical models. We will use archival infrared, optical, UV and X-ray data, supplemented with ground-based observational data from literature for a sample of 12 disks spanning a range of stellar masses, disk conditions and evolutionary epochs. 

A comparison of the stellar and disk properties that result in differing disk evolutionary outcomes will reveal the physical and chemical processes that drive disk evolution and determine the planet forming potential of disks. From our study of a varied sample of disks and from a careful characterization of their dust and gas content, we will establish disk masses and surface density distributions, infer the processes that affect surface density distributions (e.g., holes and outer radius), and estimate photoevaporation rates and disk lifetimes. These studies for a sample of varied disks will help us understand the underlying causes of disk diversity.