The Effects of Axial Rotation on the Equivalent Widths of Spectral Lines. I. Weak Resonance Lines

In this paper we shall undertake the analysis of the effects of axial rotation upon the formation of weak resonance lines in early-type stars. We shall demonstrate that the primary effects on the line strengths are due to the geometry of the distortion and the center-to-limb variation of the line strengths. Variation of the parameters defining the stellar interior will affect the line strength only to a very limited degree. We shall show that the effects of rotation upon a pure scattering line are qualitatively different from a pure absorption line. It is suggested that the moderately small changes in line strength predicted for scattering lines and the relatively large color changes may imply a scatter in the relationship between photometric color and spectral type