ABSTRACT
Observations of the equivalent width of D3 He I A 5876 in 14 main-sequence stars in the Hyades show that stellar activity in these stars is closely similar to that seen in early F-type field stars. The onset of activity occurs at about (B - V) = 0.30 m, and the activity level in stars bluer than (B - V) = 0.45 m does not correlate with rotation. There is no evidence of a decline of activity with increasing age during the rather narrow time interval spanned by the main-sequence lifetimes of early F-type stars. The sharp minimum in lithium abundance that is seen in Hyades stars of middle F spectral type occurs at about the color that marks the boundary between temperature regimes where activity does and does not correlate with rotation.