THE PHOENIX BT-SETTL 2015 MODELS BY FRANCE ALLARD AND COLLABORATORS These models are synthetic stellar and substellar atmosphere spectra produced using the PHOENIX atmosphere code and the BT-Settl model framework developed by France Allard and collaborators. The BT-Settl models are intended for cool stars, brown dwarfs, and planetary-mass objects, and include a treatment of atmospheric cloud formation and settling. The models use static, spherically symmetric, one-dimensional atmosphere calculations to describe the atmospheric emission spectrum. The BT-Settl model framework includes molecular opacities and updated physical inputs relevant to cool atmospheres. The associated research describes updates to molecular line lists and solar abundances, as well as atmospheric convection parameters calibrated using two- and three-dimensional simulations. More information about the underlying research can be found in Baraffe et al. (2015) and Allard et al. (2012). The original models were obtained from the PHOENIX repository at: https://phoenix.ens-lyon.fr/Grids/BT-Settl/CIFIST2011_2015/SPECTRA They are also available through the PHOENIX simulator: http://phoenix.ens-lyon.fr/simulator/index.faces Each file in this suite contains a spectrum for a single effective temperature, metallicity, and surface gravity. The models provided here have solar metallicity, [M/H] = -0.0, and surface gravity, log_g = 5.0. The effective temperatures range from 1200 K to 3500 K. The naming convention for the files is: phoenixm___2011.fits For example: phoenixm0.0_1200_5.0_2011.fits corresponds to a model with [M/H] = -0.0, Teff = 1200 K, and log_g = 5.0. In this naming convention, the "m" identifies the metallicity portion of the filename, the numerical value following it gives the metallicity [M/H] =log10 relative to solar, the second numerical value gives the effective temperature in kelvin, and the third numerical value gives the surface gravity log_g. The "2011" suffix is retained from the original model naming convention. This suite contains 24 model files covering Teff = 1200–3500 K in 100 K increments, all with [M/H] = -0.0 and log_g = 5.0. The wavelength range and sampling of the files differ from those of the original PHOENIX models. The spectra were resampled using pysynphot to 300,000 data points spanning approximately 10 Angstroms to 35 microns. This resampling was necessary for compatibility with STScI tools like stsynphot and the Exposure Time Calculator (ETC). Wavelengths are provided in Angstroms, and fluxes are provided as FLAM. Each file contains the wavelength array and the corresponding model flux for the single model specified by its filename. The models were downloaded from the PHOENIX repository on April 29, 2021, and were subsequently updated using the Jupyter notebook "convert_phoenix_to_synphot-one-logg." At that time, the files available at the repository had been last updated on March 16, 2015. The exact version-control history of the original model grid could not be determined. These dates are therefore provided to document the provenance of the files available in this distribution. This update extended the wavelength coverage to 10 Angstroms and resolved oscillations at short wavelengths. The updated files were also validated by checking the correspondence of their absorption features with those in the original models. The original BT-Settl 2015 spectra and the STScI-resampled files are not identical. The STScI files are derived products intended for use with STScI software and should not be treated as the original PHOENIX model spectra. Users requiring the original sampling or the complete model grid should obtain the models directly from the PHOENIX repository. References: * Baraffe, I., Homeier, D., Allard, F., & Chabrier, G. 2015, A&A, 577, A42, "New evolutionary models for pre-main sequence and main sequence low-mass stars down to the hydrogen-burning limit." https://arxiv.org/abs/1503.04107 * Allard, F., Homeier, D., & Freytag, B. 2012, Philosophical Transactions of the Royal Society A, 370, 2765. Also available through the PHOENIX model repository: * https://phoenix.ens-lyon.fr/Grids/BT-Settl/CIFIST2011_2015/SPECTRA * http://phoenix.ens-lyon.fr/simulator/index.faces