Hubble Space Telescopespectrophotometry and Models for Solar Analogs

Absolute flux distributions for seven solar analog stars are measured from 0.3 to 2.5 μm by Hubble Space Telescope ( HST) spectrophotometry. In order to predict the longer wavelength mid-IR fluxes that are required for James Webb Space Telescope calibration, the HST spectral energy distributions are fit with Castelli & Kurucz model atmospheres; and the results are compared with fits from the MARCS model grid. The rms residuals in 10 broadband bins are all <0.5% for the best fits from both model grids. However, the fits differ systematically: the MARCS fits are 40–100 K hotter in T eff , 0.25–0.80 higher in log g , 0.01–0.10 higher in log z , and 0.008–0.021 higher in the reddening E ( B − V ), probably because their specifications include different metal abundances. Despite these differences in the parameters of the fits, the predicted mid-IR fluxes differ by only ∼1%; and the modeled flux distributions of these G stars have an estimated ensemble accuracy of 2% out to 30 μm.