Cosmic Beacons Towards a Theory of Massive Star Formation - A NIR View of the Most Luminous Protostars

Massive stars have dramatic impacts throughout the universe, but their birth, deep within dusty molecular clouds, is literally shrouded in uncertainty. However, during this process, powerful outflows blast open low density cavities and NIR light shines out from the forming star, beamed as if from a lighthouse through turbulent storm clouds. This light carries crucial information that can guide us to a deeper understanding of massive star formation. We propose WFC3/IR observations of 10 high-luminosity protostars, selected to already have well-studied properties via MIR-FIR data. The sources, along with 5 others with archival HST images, form a sample to be analyzed uniformly with the following goals: 1) Characterize J & H band continuum emission from massive protostars, including faint, extended emission. Radiative transfer simulations show such NIR emission is mostly scattered light emerging from outflow cavities, thus enabling measurement of their structure, radiation fields & dust content; 2) Detect Pa-beta & [FeII] emission tracing shock- & photo-ionized regions, important diagnostics of the protostars and their outflows; 3) Search for low-mass stars that may be clustered around the massive protostars, as predicted in Competitive Accretion models, with the observations especially probing in the low extinction outflow cavities. WFC3/IR's sensitivity, angular resolution and field of view are essential for this study. The project allows a first exploration of correlations of outflow and cluster environment properties with basic protostellar parameters, e.g., mass, luminosity & evolutionary stage, and thus enables groundbreaking tests of massive star formation theories.