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B.L. Rachford (Univ. of Wyoming)
Using high-precision observations of the \ion{He}{1} \lambda5876 (D3) line we have searched for short-term chromospheric variability in three nearby early F-type stars. In one star, 18 Bootis, we find variability at a level more than twice that of the individual measurement uncertainties, while the other two stars appear constant or only slightly variable. The variability in 18 Bootis amounts to a factor of 2 in equivalent width. During some nights the variability occurs on times scales of two hours or less, but on other nights the activity remains constant. The variability does not show any significant periodicities and does not appear to correlate with rotation. We find highly significant (P > 0.995) correlations between line width and line strength, and line center and strength. The latter correlation is in the sense of a bluer line for increasing strength, perhaps indicating increased outflow of material with increased activity.
The author(s) of this abstract have provided an email address for comments about the abstract: rachford@uwyo.edu