Modeling the near-UV band of GK stars, Paper III: Dependence on abundance pattern

TL;DR

This study investigates how different abundance patterns and NLTE modeling affect the determination of stellar parameters from the near-UV spectra of GK stars, highlighting the importance of chemical composition and wavelength region in spectral fitting.

Contribution

It extends NLTE spectral models to include updated abundance patterns and alpha-enhancement, analyzing their impact on effective temperature and gravity estimates from observed spectra.

Findings

GASS10 abundances slightly lower T_eff for late-type giants

NLTE models with GASS10 better match T_eff calibrations

Fitting results depend on wavelength region and line blanketing effects

Abstract

We extend the grid of NLTE models presented in Paper II to explore variations in abundance pattern in two ways: 1) The adoption of the Asplund et al. (2009) (GASS10) abundances, 2) For stars of metallicity, [M/H], of -0.5, the adoption of a non-solar enhancement of alpha-elements by +0.3 dex. Moreover, our grid of synthetic spectral energy distributions (SEDs) is interpolated to a finer numerical resolution in both T_eff (Delta T_eff = 25 K) and log g (Delta log g = 0.25). We compare the values of T_eff and log g inferred from fitting LTE and Non-LTE SEDs to observed SEDs throughout the entire visible band, and in an ad hoc "blue" band. We compare our spectrophotometrically derived T_eff values to a variety of T_eff calibrations, including more empirical ones, drawn from the literature. For stars of solar metallicity, we find that the adoption of the GASS10 abundances lowers the inferred T_eff value by 25 - 50 K for late-type giants, and NLTE models computed with the GASS10 abundances give T_eff results that are marginally in better agreement with other T_eff calibrations. For stars of [M/H]=-0.5 there is marginal evidence that adoption of alpha-enhancement further lowers the derived T_eff value by 50 K. Stellar parameters inferred from fitting NLTE models to SEDs are more dependent than LTE models on the wavelength region being fitted, and we find that the effect depends on how heavily line blanketed the fitting region is, whether the fitting region is to the blue of the Wien peak of the star's SED, or both.