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K. G. Carpenter (NASA's GSFC), R. D. Robinson (JHU)
We have assessed important parameters of the stellar winds of two very similar M giant stars, Gamma Cru (M3.5III) and Mu Gem (M3III), using high resolution HST/GHRS spectra and found surprising differences in the characteristics of their winds and in their total mass-loss rates. The wind parameters, including flow and turbulent velocities, the optical depth of the wind above the region of photon creation, and the mass-loss rate, have been estimated by fitting line profiles computed using the "Sobolev with Exact Integration" (SEI) radiative transfer code (Lamars et al. 1987), along with simple models of the outer atmospheric structure and wind. These computed profiles are fit to chromospheric emission lines which show self-absorptions produced by the photon-scattering winds of these stars. The SEI code has the advantage of being computationally fast and allows a great number of possible wind models to be examined. The analysis is iterative in nature: we specify estimates of the wind parameters, calculate line profiles for the Mg II (UV1) lines and a range of unblended Fe II lines (which have a wide range of wind opacities and therefore probe different heights in the atmosphere), compare the computed profiles with the observations, and modify the assumed wind properties until the predicted profiles match the observations over as many lines as possible.. Surprisingly, we find that the Gamma Cru wind exhibits a significantly higher terminal velocity, wind turbulence, and mass-loss rate than its fellow M-giant Mu Gem.
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Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.