| Description |
Very massive stars are infrequently found in the unvierse. However, their influence is substantial in terms of ionization flux and total stellar wind luminosity in local star forming regions. They are also believed to be very important in the earliest star forming era ofthe universe where metallicities are low and more massive stars are prefentially formed. Evolved massive stars later become thesites of type II supernova explosions. However, our understanding of the evolution of very massive stars is relatively limited, and manyevolutionary sequences are still possible. A fundamental set of properties for understanding the evolution of very massive is therehistorical mass-loss. This is, in effect, imprinted on their surroundings. Wolf-Rayet stars are believed to be the evolutionary endpoints of very massive main-sequence O stars before they become supernovae. Many are known to have ring nebulae of material, most frequently found from the detection of ionized shells. Probing these shells should provide better constraints as to the mass of materials (and evolutionof these materials) lost during the heavy mass-loss phases that are believed to occur prior to the Wolf-Rayet phase of a star.But the lack of understanding of particularly cooler material in ejecta has made this task difficult. The use of higher resolution far-infrared sata from {it Herschel} PACSand SPIRE data on large nebulae should enable the structures of cool materials to be finally determined and masses measured in such nebulae.In the proposed project, we investigate the environments of five Wolf-Rayet stars at high galactic latitude, which considerably reducing line ofsight and confusion problems found in the plane of the galaxy. Most have evidence of molecular/neutral materials from prior measurements.Our intent is to measure the mass, indicate the extent of clumping and cool materials in the nebulae, plus searching for evidence of extended low-levelemission structures and any evidence of multiple ejections. |
