Though their field was once thought to be reasonably well-understood, astronomers in the massive-star community are now faced with a number of new and fundamental questions about the non-spherical character of stellar mass loss. The nature and extent of wind clumping remains an unsolved problem; recent studies suggest that due to this clumpiness, O star mass-loss rates should be revised downward by an order of magnitude or more. In addition, a growing body of evidence shows that magnetic fields can influence the geometry of mass loss in hot star winds in unanticipated ways. The effects of stellar rotation on the structure and formation of disks around some main sequence and post-main sequence massive stars are still not fully understood. Meanwhile, detailed observations of supernovae reveal that many more core-collapse objects interact extensively with aspherical circumstellar environments than previously realized, and signatures of this interaction may be mined for clues to the mass-loss histories of massive supernova progenitors.
This project is a comprehensive study of clumpy and aspherical structures in the circumstellar media of massive stars and supernovae. Motivated by access to high-resolution spectropolarimetric data and using an established Monte Carlo radiative transfer code, Drs. Ignace and Hoffman, and their team, will construct simulations of variable line and continuum polarization in the stochastically clumped winds of Wolf Rayet, luminous blue variable, and O stars; in the disks and rotating magnetospheres of other active stars; and in core-collapse supernovae interacting with their immediate environments. They will also develop algorithms that will allow the modeling code to simulate line polarization arising from the Zeeman and Hanle effects from the circumstellar fields of magnetized stars. The investigators have broad experience in both radiation transport techniques and interpreting spectropolarimetric observations of hot star winds and interacting supernovae. By confronting detailed 3D models of these systems with multiwavelength and polarimetric data, the goal is a better understanding of how the mass-loss history of main-sequence and evolved massive stars can be extracted from their observation and those of core collapse supernovae.
The project includes a unique outreach program, Promoting Careers in Science, through which Drs. Ignace and Hoffman will each implement innovative strategies for improving science education and literacy in their respective communities. Dr. Ignace will reach out to school counselors to enhance science education among Appalachian middle- and high-school students. Dr. Hoffman will partner with the University of Denver's Women's College to create new entry points into the scientific career 'pipeline' for non-traditional female undergraduate students. In addition, Dr. Ignace will continue supervising undergraduate research projects both through East Tennessee State University and through involvement in an REU site program. The bulk of the 5-year funding will go to support the training and professional development of a postdoctoral researcher at East Tennessee State University and a graduate student at the University of Denver who will be trained in the theoretical modeling of radiation transfer.
