Computer Science – Sound
Scientific paper
Mar 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008aas...21116215a&link_type=abstract
American Astronomical Society, AAS Meeting #211, #162.15
Computer Science
Sound
Scientific paper
HST/GHRS, HST/STIS and FUSE observations of evolved late-type stars demonstrated the presence of non-thermally broadened UV emission lines forming at temperatures of 10,000 to 300,000K in almost all of the stars. In this study we analyze CI 1993.62A, CII] 2323.5A, SiIII 2350.17A, SiIV 1393A, CIII 977A, OIV 1401.35A and OVI 1032A emission lines from Tau. Our analysis of these UV lines reveal redshifts T (except for OVI 1032A), while non-thermal velocities T . Derived emission measures indicate filling factors <0.1%. These findings force us to reconsider the definition of chromospheric and transition regions in these stars as patchy regions or atmospheric hot spots. According to Freytag et al. (2002), convective cells with sizes of 0.01Rstar generate shock waves that dissipate at lower atmospheric layers. Large-scale convective motions produce large-scale magnetic structures in contrast to arcades of thin solar-like loops powered by small-scale granular motions. We discuss the model of non-linear Alfven waves amplified by resonant interaction with sound waves and propagating upward along one (or a few) constant pressure large-scale loop(s). As Alfven waves propagate upward in a gravitationally stratified atmosphere, their wave amplitudes increase causing non-thermal broadening in UV lines due to unresolved wave motions. We discuss a model that predicts downward plasma motions in extended loops driven by asymmetric Alfven wave heating. We use a state-of-the-art 2.5 MHD code to show that the energy flux density of Alfven waves (with P a few days), which are needed to explain the radiative cooling and non-thermal broadening in the UV lines, is consistent with the requirement to drive massive ( 10 MSun/yr) and slow ( 30 km/s) stellar winds from magnetically open structures with the assumption of a magnetic field at the wind base 1 G.
This research is supported by the NASA Research grant to CUA from GSFC No. NASA-NNG06GJ29G
Airapetian Vladimir
Carpenter Kenneth G.
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