Imaging the Dynamic Atmospheres of Evolved Stars at Radio Wavelengths

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Aging low-to-intermediate mass stars recycle up to 80% of their mass back to the interstellar medium. This is a primary source of dust and heavy metal enrichment in the Galaxy, yet the details of the stellar mass loss process are poorly understood. Principal Investigators (PIs) Matthews and Akiyama will study the dynamic, mass-losing atmospheres of evolved stars with the Karl G. Jansky Very Large Array (VLA) and the Atacama Large Millimeter/submillimeter Array (ALMA). The PIs will develop and test new computer algorithms to improve the image resolution so that they can “see” new details of the stellar radio photospheres. The PIs will investigate changes in the photospheres on timescales of weeks to months as well as the physical processes that launch the stellar wind. The new software will be released to the broader astronomical community for use in imaging studies ranging from protostellar disks and jets to black hole event horizons. The PIs will collaborate with science media specialists to produce and distribute three public podcasts about “Radio Stars”. A key component of this work will be the development and testing of new high-resolution imaging techniques based on regularized maximum likelihood methods. The resulting continuum images will enable measurements of fundamental stellar parameters (including photospheric diameters, shapes, and brightness temperatures), as well as resolved imaging of stellar surface features and the exploration of secular changes in the radio photospheres. Contemporaneous observations of spectral lines from adjacent atmospheric regions will provide complementary diagnostics of chemistry, density, temperature, and gas kinematics. These results will be compared with model predictions to provide new insights into the roles of convection, shocks, and pulsation in driving evolved star winds. The new imaging algorithms will be made available in the Common Astronomy Software Applications (CASA) package. To engage the public and broaden participation the team will include sonification of radio data in their podcasts.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.