Far-ultraviolet continuum of G-type stars: a signature of the temperature minimum region.
FRANCHINI M., MOROSSI C. and MALAGNINI M.L.
Abstract (from CDS):
The main results of a program of systematic comparison between observed and computed UV spectral energy distributions of field G-type stars are illustrated. We constructed the UV observed energy distributions for 53 G stars, starting from the IUE Uniform Low Dispersion Archive (ULDA) and computed the corresponding theoretical fluxes by using the atmospheric parameters from the Catalogue of [Fe/H] Determinations (1996 edition) and a Kurucz grid of model fluxes. From the comparison between observations and classical models, a UV excess shortward of 2000 Å is evident for all the program stars. The UV continuum in the region 1600-2000 Å can be described by synthetic fluxes computed from semiempirical models based on the temperature minimum concept. Values for the Tmin/Teff ratio on the order of 0.80 are suitable for the interpretation of the observed fluxes. The residual discrepancies shortward of 1600 Å are suggested to be effects of the chromosphere, on the basis of a comparison with the Maltby et al. semiempirical model of the Sun.