# A New Stellar Atmosphere Grid and Comparisons with HST/STIS Calspec Flux Distributions

## TL;DR

This paper introduces a new stellar atmosphere grid based on LTE and NLTE models, compares it with existing grids using HST/STIS flux data, and makes it available for JWST observations.

## Contribution

A comprehensive new LTE stellar atmosphere grid (BOSZ) is developed, compared with existing models, and extended to include NLTE models for hot stars, improving spectral fitting accuracy.

## Key findings

- BOSZ grid provides better IR sampling than CK04.
- The fit for Sirius' angular diameter matches interferometric measurements.
- NLTE models do not smoothly transition to LTE models at 15,000K.

## Abstract

The Space Telescope Imaging Spectrograph (STIS) has measured the spectral energy distributions (SEDs) for several stars of types O, B, A, F, and G. These absolute fluxes from the CALSPEC database are fit with a new spectral grid computed from the ATLAS-APOGEE ATLAS9 model atmosphere database using a chi-square minimization technique in four parameters. The quality of the fits are compared for complete LTE grids by Castelli & Kurucz (CK04) and our new comprehensive LTE grid (BOSZ). For the cooler stars, the fits with the MARCS LTE grid are also evaluated, while the hottest stars are also fit with the NLTE Lanz & Hubeny OB star grids. Unfortunately, these NLTE models do not transition smoothly in the infrared to agree with our new BOSZ LTE grid at the NLTE lower limit of Teff =15,000K. The new BOSZ grid is available via the Space Telescope Institute MAST archive and has a much finer sampled IR wavelength scale than CK04, which will facilitate the modeling of stars observed by the James Webb Space Telescope (JWST). Our result for the angular diameter of Sirius agrees with the ground- based interferometric value.