The Physics of Star Formation : Understanding

We propose to bring the power of NGST to bear on one of the most important problems in star formation { understanding protostellar formation from parent molecular cores and subsequent evolution towards becoming young stars. A few extremely young (10 < < 10 yr) protostars have nally been discovered with sub-millimeter telescopes in recent years, but the high extinctions (Av > 400 mag) towards their central regions have prevented detailed study of their inner structures and mass accretion properties. Thus many key questions of the star formation process remain unanswered, such as: What determines the nal mass of a forming star; do initial conditions of the ambient gas play the dominant role, or does feedback from the process itself x stellar mass? How do protostellar envelopes evolve from pre{stellar cores to star+disk systems, and is the actual process consistent with our current theoretical models? When and under what conditions do binary systems form? What are the accretion histories of protostellar objects? When do protostellar disks form and when are jets rst launched from the system? We propose to answer these questions by undertaking a program of mid-IR imaging and spectroscopic observations of protostellar sources with NGST. We will probe the infalling envelopes, central objects, accretion disks, and accretion{powered jets from protostars which are still accreting the bulk of their masses. These observations will be used to infer the morphologies and density structures of infalling circumstellar envelopes, measure the binary frequency of protostars, determine envelope infall rates from shocked line emissions, and evaluate mass out ow rates and accretion histories from observations of jets. This information will be crucial in determining the process by which stars and disks are assembled from molecular cloud cores and for understanding what mechanisms regulate stellar masses and determine the initial mass function. ASWG DRM Proposal The Physics of Star Formation: Understanding the Youngest Protostars