THE ATMOSPHERIC PARAMETERS OF A-STARS AND F-STARS .1. COMPARISON OF VARIOUS METHODS

We present a detailed investigation into the methods of determining th e atmospheric parameters of stars in the spectral range A3 - F5, inclu ding metallic-lined (Am) stars. The systematic differences in effectiv e temperature (T(eff)) and surface gravity (log g) obtained by Lane & Lester (1984) and Dworetsky & Moon (1986) for Am stars are evaluated. A flux excess at 4785 angstrom proposed by Lester (1987) as the reason for uvbybeta photometry giving higher T(eff) and log g values than sp ectrophotometry is investigated. Spectroscopic observations of this re gion show no sign of any excess. We find that the flux excess is cause d by a depression in older model fluxes caused by an excess of CI opac ity. Medium-resolution spectra of Hbeta and Hgamma line profiles are u sed to obtain the T(eff) for 52 A and F stars. The results are in agre ement with those from uvbybeta photometry. Spectrophotometric T(eff) a nd log g given by Lane & Lester are shown to be too low, due to insuff icient allowance for metal abundance ([M/H]). Using an appropriate [M/ H] gives T(eff) and log g in good agreement with those given by uvbybe ta and Balmer lines.