Smith, Graeme H., Dupree, Andrea K., and Strader, Jay. 2012. "The ?10830 He I Absorption Line Among Metal-Poor Subdwarfs." Publications of the Astronomical Society of the Pacific 124:1252-1261. https://doi.org/10.1086/668865
Spectra of the He I ?10830 line have been obtained for 23 metal-poor stars, the majority of which are dwarfs ranging in metallicity from 2.1 = [Fe/H] = -0.8. The data were acquired with the NIRSPEC spectrograph on the Keck II telescope. Most of these subdwarfs and dwarfs are found to exhibit a He I absorption line indicative of the presence of chromospheres. The equivalent width of the ?10830 absorption profile is generally less than 70 mÅ, and covers a range similar to that found in solar metallicity stars of low activity. Among the subdwarfs the lambda;10830 equivalent width does not correlate with either [Fe/H] metallicity or (B-V) color. Some evidence for asymmetric profiles is found among metal-poor dwarfs, but not the high-speed blue-shifted absorption displayed by some metal-poor red giants.