AAS 205th Meeting, 9-13 January 2005
Session 53 Hot Stars, Atmospheres and Winds
Poster, Tuesday, January 11, 2005, 9:20am-6:30pm, Exhibit Hall

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[53.02] TEXES Observations of Betelgeuse: Dynamics and Thermodynamics of the Wind Acceleration Zone

G. M. Harper, A. Brown (U. Colorado), M. J. Richter (UC Davis), S. Holmes (U. Texas), N. A. Ryde (Uppsala U.)

We have detected Fe~II 17.94 & 24.52\mum, and Fe~I 24.04\mum forbidden line emission in Betelgeuse (M2~Iab) using the Texas Echelon Cross Echelle Spectrograph (TEXES). These optically thin emission lines are resolved at R~q 50,000 and provide new diagnostics of the dynamics and thermodynamics of the wind acceleration zone. The [Fe~II] lines, from the first excited term (a\>4F), are sensitive to warm plasma where energy is deposited by currently unknown mechanisms into the wind flow. These diagnostics complement previous ISO observations which were sensitive to the cooler more extended atmosphere.

The turbulence observed in the forbidden lines is smaller than found in the chromosphere from the C~II] 2325Å {}lines. We compare predictions from different semi-empirical models with the observed line profiles. We have also detected [Fe~II] emission in two other M supergiants, 119~Tau and \alpha~Her.

This research was supported by NSF grant AST-0206367 and NASA grant NNG04GD33G. MJR acknowledges grants NSF 0307497 and NASA NNG04GG92G. TEXES was built and the observations funded by grants from NSF and Texas Advanced Research Program.

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