The Early F-Type Stars: Refined Classification, Confrontation with Stroemgren Photometry, and the Effects of Rotation

The classification for early F-type stars in the MK spectral classification system presented by Gray and Garrison (1987) is refined. The effect of rotation on spectral classification and ubvy-beta photometry of early F-type stars is examined. It is found that the classical luminosity criterion, the 4417 A/4481 A ratio gives inconsistent results. It is shown that most of the stars in the Delta Delphini class of metallic-line stars are either normal or are indistinguishable from proto-Am stars. It is suggested that the designation Delta Delphini should be dropped. The classifications are compared with Stromgren photometry. The effects of rotation on the delta-c₁ index in the early-F field dwarfs is demonstrated.