THE PHYSICAL BASIS OF THE SPECTRAL CLASSIFICATION OF A, F AND G STARS

We present the first results of a precise scheme for spectral classification for the late B, A, F and early G-type stars. We have used ∼15000 well classified stars from (Hauck & Mermilliod 1998) and with the Stromgren (b−y), [c1] and [m1] indices (Stromgren 1951) to define the regions in the [m1]-[c1] diagram. We also generate calibrations for the effective temperature (Teff ) and the surface gravity.