Assigned ID: 287 ----- Attempting Submission 1 (Fri Feb 25 05:53:14 GMT 2011) ----- HST Phase I Proposal 287 (cycle19_ar.apt) successfully submitted. ----- Attempting Submission 2 (Fri Feb 25 17:35:41 GMT 2011) ----- HST Phase I Proposal 287 (cycle19_ar.apt) successfully submitted. ----- Attempting Submission 3 (Fri Feb 25 17:37:55 GMT 2011) ----- HST Phase I Proposal 287 (cycle19_ar.apt) successfully submitted. ----- Attempting Submission 4 (Fri Feb 25 20:55:51 GMT 2011) ----- HST Phase I Proposal 287 (cycle19_ar.apt) successfully submitted. ----- Attempting Submission 5 (Fri Feb 25 21:44:44 GMT 2011) ----- Understanding the evolution of young stellar objects (YSOs) from a protostar to a main-sequence star is key to understanding the origins and evolution of planetary systems. High-resolution polarimetric observations from both NICMOS and ACS of objects known to span the earliest stellar evolutionary phases will be combined with (1) 3-D radiative transfer codes, and (2) a grid of dust grain models, to gain insight into the initial phases of dust grain growth and evolution away from an ISM distribution. Fractional polarization is a strong function of wavelength; therefore by developing detailed models of polarimetric images in the optical and infrared, we can sensitively constrain not only the geometry and optical depth of the scattering medium, but also the grain size distribution. We will study 15 YSOs known to span the earliest stellar evolutionary phases (Class I – Class III) as their circumstellar disks transition from containing primarily small ISM dust grains to larger size grains indicative of protoplanetary disks. Full modeling of this data set will enable us to specifically address the evolution of the small grain distribution as a function of evolutionary state, and the implications of the early evolution of dust grains on planetary formation. We will make our grid of polarization images publicly available, providing a resource to the community to interpret other datasets.

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