The Physical Basis of Luminosity Classification in the Late A-, F-, and Early G-Type Stars. I. Precise Spectral Types for 372 Stars

This is the first in a series of two papers that address the problem of the physical nature of luminosity classification in the late A-, F-, and early G-type stars. In this paper, we present precise spectral classifications of 372 stars on the MK system. For those stars in the set with Strömgren uvbyβ photometry, we derive reddenings and present a calibration of MK temperature types in terms of the intrinsic Strömgren (b-y)₀ index. We also examine the relationship between the luminosity class and the Strömgren c₁ index, which measures the Balmer jump. The second paper will address the derivation of the physical parameters of these stars, and the relationships between these physical parameters and the luminosity class. Stars classified in this paper include one new λ Bootis star and 10 of the F- and G-type dwarfs with recently discovered planets.