Title:Physical and Chemical Structures of Low-Mass Protostars on the Disk-Forming Scale

Yoko Oya (Univ. of Tokyo)


Disk-formation around protostars is of fundamental interest for both of astrophysics and astrochemistry, because protostellar/protoplanetary disks are the birthplaces of planets.  With the advent of ALMA (Atacama Large Millimeter/submillimeter Array), infalling envelope and rotating disks are spatially resolved in radio observations.  We have delineated physical and chemical structures around several young (Class 0/I) low-mass protostellar sources with ALMA.  On a 100 au scale, chemical compositions of the gas have been found to drastically change from envelopes to disks.  This chemical change helps us to disentangle the kinematic structures of the gas into the two fundamental components (an envelope and a disk), like `molecular markers’.  More interestingly, the chemical characteristics on a disk scale are different among sources, as previoiusly reported for the cloud core scale (~1000 au).  On a 10 au scale, finer structures in disks are being delineated;  in IRAS 16293-2422 Source A, the kinetic temperature of H2CS increases locally at the boundary between the envelope and the disk.  This feature indicates a weak accretion shock and/or thermal heating in the transition zone, and moreover, it would be responsible to the drastic chemical change.  The 1.2 mm continuum emission from this source also shows sub-structures in the disk.  The connection from envelopes into disks is thus the current target for observational studies from both the physical and chemical aspects.  The physical/chemical changes and the chemical diversity of young low-mass sources will have a substantial impact on understanding the initial condition of disk/planetary formation.

Host contact: Hideaki Takemura