Poster Open Access

Semi-Empirical Analyses of Alfvén Wave-Driven Winds from Red Giants and Supergiants

Harper, Graham M

We present a synopsis of ongoing projects that are analyzing the properties of outflows (winds) from cool evolved non-dusty stars with spectral-types K through mid-M.  These projects include: (1) A semi-empirical study of the inferred  Alfvén wave properties required to drive the rapidly accelerating winds from single red giants, and the more gradual acceleration of the eclipsing binary zeta Aurigae (K4 Ib + B5 V).  The results includes a revision of previous published radial dependent damping lengths. (2) The first determination of the outflow radial gradients of the gas temperature and turbulence in Arcturus  (alpha Boo: K1.5 III) and Aldebaran (alpha Tau: K5 III) based on radiative transfer modeling of HST-STIS emission line profiles, including a new significantly reduced mass-loss rate for alpha Boo. (3) A novel semi-empirical mass-loss rate expression for K through mid-M red supergiants based on optically thin 17.94\,$\mu$m [Fe II] emission line fluxes collected with TEXES at the NASA-IRTF.  This approach is based on a dominant ionization state within the base of the wind and it has the potential to overcome the limitations of CO and dust estimates because these are not fully associated in warm supergiant winds.


Support for program numbers HST-AR-14566-001-A, HST-GO-14731-001-A, and HST-GO-15234.001-A was provided by NASA through grants from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555.  The TEXES spectra were obtained at the Infrared Telescope Facility, which is operated by the University of Hawaii under contract 80HQTR19D0030 with the National Aeronautics and Space Administration.
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