The late A-type stars - Refined MK classification, confrontation with Stromgren photometry, and the effects of rotation

Abstract

The MK spectral classification for late A-type stars is refined and the effects of rotation of spectral classification and uvby(beta) photometry for these stars are examined. It is found that, for A3 stars, the 4417/4481 A wavelength ratio produces results that are inconsistent with the Stark broadening of the H lines. It is suggested that this ratio is not useful as a luminosity criterion at any spectral type. Self-consistent sequences of narrow- and broadline standards are established. The results of the refined classification system are compared with Stromgren photometry, showing a set of low-v sin i A-type stars with anomalously large delta(c<SUB>1)</SUB> indices for their luminosity types. It is proposed that these stars are rapid rotators seen at fairly low inclination angles.