AAS 197, January 2001
Session 44. Observations and Analysis of Stellar Atmospheres
Display, Tuesday, January 9, 2001, 9:30am-7:00pm, Exhibit Hall

## [44.14] The Physical Basis of Luminosity Classification in the Late A, F and early G--type Stars

R.O. Gray (Appalachian State University), P.W. Graham (Appalachian State University), S.R. Hoyt (Appalachian State University)

Classification--resolution CCD spectra (1.8Å/2 pixels) of high quality (S/N> 300) have been obtained for nearly 400 A5 -- G5 stars of all luminosity classes (V -- Ib) on the 0.8 meter telescope of Appalachian State University's Dark Sky Observatory. These spectra have been classified carefully on the MK Spectral Classification system. The basic parameters for these stars, T\rm{eff}, \log g, [M/H] and \xit, the microturbulent velocity, have been determined using a multidimensional simplex routine which finds the best fit to the observed spectrum and fluxes (from Strömgren uvby photometry) from a four--dimensional grid of synthetic spectra and fluxes calculated from Kurucz models. Internal errors are approximately ±80K in T\rm{eff}, ±0.10 in \log g, ±0.10 in [M/H] and ±0.5km/s in \xit, the microturbulent velocity.

The results have been examined for correlations between \log g, \xit and the luminosity class. Using partial correlation analysis, it is found that for most spectral types the microturbulent velocity is as good or better a predictor of the luminosity type as the gravity. The implications of this result for the interpretation of luminosity classification on the MK Spectral Classification system will be discussed.