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AR 14566 (Archival Research)

Thu Jul 25 12:31:41 GMT 2024

Principal Investigator: Graham Harper
PI Institution: University of Colorado at Boulder
Investigators (xml)

Title: Constraining Theroretical Wind Models using the Accelerating Outflows of Cool Evolved Stars as revealed by Hubble
Cycle: 24

Abstract
The vacuum ultraviolet (UV) contains many strong transitions of neutral and singly ionized atomic species that allow the outflows (winds) from cool evolved stars to be mapped through their scattering line profiles. The high spectral resolution and high signal-to-noise ratios, and excellent noise characteristics of Hubble spectra permit the study of the poorly understood processes that drive outflows from red giant stars. The high spectral resolution has revealed that the outflows have low intrinsic UV emission and they accelerate with velocities systematically increasing outwards, rather than occurring through ballistic ejections from the surface. HST spectra have provided numerical constraints on wind speeds, turbulence, and mass-loss rates but they have not been fully exploited to study the important underlying physics of the wind driving process. We propose a study, within the framework of wave-driven outflows, to infer the radial wave-pressure gradients required to drive the observed winds and derive implied heating rates for well-studied single red giants. These will be used to study magnetic wave frequencies, flow geometries, damping mechanisms, and thus provide new physical insights into the poorly understood mass loss process. The results will also provide improved constraints for physically motivated mass-loss rate expressions for use in stellar evolution codes.