HST Spectrophotometry and Models for Solar Analogs

TL;DR

This study measures the flux distributions of seven solar analogs using HST spectrophotometry and fits them with stellar atmosphere models to predict mid-infrared fluxes for JWST calibration, achieving about 2% accuracy.

Contribution

It provides a detailed comparison of Castelli & Kurucz and MARCS model fits to observed spectra, improving mid-IR flux predictions for solar analogs.

Findings

Both models fit the data with residuals <0.5% in broad bands.

Model parameters differ systematically, but predicted mid-IR fluxes agree within ~1%.

Modeled flux distributions have an estimated accuracy of 2% up to 30 μm.

Abstract

Absolute flux distributions for seven solar analog stars are measured from 0.3 to 2.5 \mu m by HST spectrophotometry.In order to predict the longer wavelength mid-IR fluxes that are required for JWST calibration, the HST SEDs are fit with Castelli & Kurucz model atmospheres; and the results are compared with fits from the MARCS model grid. The rms residuals in 10 broad band 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 \mu m.