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J. L. Blum, A. K. Dupree (CfA), I. I. Ilyin (Astrophysical Institute Potsdam), D. D. Sasselov (CfA)
The He I 10830{Å} line in the spectra of cool luminous stars, can reveal the dynamics of the chromosphere because the line-forming process is independent of local conditions. Following photoionization of neutral helium by the star's X-ray and EUV flux, helium recombines into a metastable state. Thus, absorption in the He I line serves as an excellent tracker of the mass outflow leading to mass loss. Using high resolution spectra from the Fourier Transform Spectrograph on the Canada-France-Hawaii telescope (CFHT) and the SOFIN echelle spectrograph on the Nordic Optical Telescope (NOT), we analyze the presence and strength of the He I \lambda10830 line to determine the chromospheric expansion velocity in 22 luminous cool stars of spectral types G and K. About half of the stars show absorption at outflowing velocities in excess of 100 km s-1 which are comparable to typical stellar escape velocities at 1 Rstar. For these targets we also explore the relation between the extent of He I \lambda10830 absorption and X-ray flux. This research was supported by the NSF REU Program at SAO.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.