Formation of massive stars by accretion requires a high accretion rate of Ṁ∗ > 10 −4 M⊙/yr to overcome the radiation pressure barrier of the forming stars. Here, we study evolution of protostars accreting at such high rates, by solving the structure of the central star and the inner accreting envelope simultaneously. The protostellar evolution is followed starting from small initial cores until...

Studies of evolved massive stars indicate that they form in a clustered mode. During the earliest evolutionary stages, these regions are embedded within their natal cores. Here we present high-spatial-resolution interferometric dust continuum observations disentangling the cluster-like structure of a young massive star-forming region. The derived protocluster mass distribution is consistent wit...

We present multi-line and continuum observations of the circumstellar environment within 10 AU of a sample of protostars to investigate how the effects of outflows on their immediate environment changes over time. CO(1-0) emission probes the high-velocity molecular outflows near the protostars and demonstrate that the outflow opening angle widens as the nascent star evolves. Maps of the CO(1-0)...

We obtained near infrared (NIR) imaging with the Subaru Telescope of the class 0 protostar candidates in the Orion Molecular Cloud-3, two of which were discovered to have X-ray emission by the Chandra X-ray Observatory. We found strong evidence for the class 0 nature of the X-ray sources. First, our deep K -band image shows no emission brighter than 19.6 mag from both of these X-ray sources. Si...

The high multiplicity of massive stars in dense, young clusters is established early in their evolution. The mechanism behind this remains unresolved. Recent results suggest that massive protostars may capture companions through disk interactions with much higher efficiency than their solar mass counterparts. However, this conclusion is based on analytic determinations of capture rates and esti...

Magnetic fields are present in a wide variety of stars throughout the HR diagram and play a role at basically all evolutionary stages, from very-low-mass dwarfs to very massive stars, and from young star-forming molecular clouds and protostellar accretion discs to evolved giants/supergiants and magnetic white dwarfs/neutron stars. These fields range from a few μ G (e.g., in molecular clouds) to...

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 th...

We investigate the formation by accretion of massive primordial protostars in the range 10 to 300 M⊙. The high accretion rate used in the models (Ṁ = 4.4 × 10 M⊙ yr ) causes the structure and evolution to differ significantly from those of both present-day protostars and primordial zero-age main sequence stars. After an initial expansion of the radius (for M∗ . 12M⊙), the protostar undergoes an...

Protostars are precursors to the nearly fully assembled T-Tauri and Herbig Ae/Be type stars undergoing quasi-static contraction towards the zero-age main sequence; they are in the process of acquiring the majority of their stellar mass. Although numerous young stars with spatially extended envelope-like structures appear to fit this description, their high extinction has inhibited observers fro...

Currently ∼36 different absorption bands have been detected in the infrared spectra of cold, dense interstellar and circumstellar environments. These are attributed to the vibrational transitions of ∼17 different molecules frozen on dust grains. We review identification issues and summarize the techniques required to extract information on the physical and chemical evolution of these ices. Both...