Physical Structures Traced by Chemical Diagnostics in Disk-Forming Regions of Young Low-Mass Protostellar Sources
Speaker: Yoko Oya
Abstract:
To understand the origin of the Solar system, the physical/chemical evolution along the star/planet formation is a key issue. With the advent of ALMA, extensive observational studies have revealed that both the physical structure and the chemical composition drastically change during the disk formation around protostars. Furthermore, it has been found that molecular distributions are sensitive to changes in the physical conditions. Some kinds of molecular lines are therefore prospected to work as ‘molecular markers’ to selectively highlight particular structures of disk forming regions.
Specifically, sulfur-bearing species have empirically been good tracers; the kinematic structures of the circummultiple structure, the circumstellar disk, and the outflow lobes are traced by the OCS, H2CS, and SO emission, respectively, in a young low-mass protostellar source IRAS 16293-2422 Source A. The gas in its circummultiple structure was found to keep falling toward its periastron even beyond its centrifugal radius, which is often assumed to be the outer edge of a Keplerian disk. Angular momentum of the gas is the essential topic to understand the structure formation. The chemical diagnostics with the aid of the molecular markers can be a helpful tool to tackle with the redistribution of the angular momentum among the disk/envelope and outflow structures. Conversely, detailed physical characterization is essential to elucidating the chemical evolution occurring there.