Accurate Gravities of F, G, and K stars from High Resolution Spectra Without External Constraints

TL;DR

This paper introduces a new spectroscopic method to accurately determine surface gravities of F, G, and K stars from high-resolution spectra without external data, achieving results consistent with asteroseismic and transit-based measurements.

Contribution

The authors develop an iterative spectral fitting procedure using SME with improved line constraints and updated models, enabling precise gravity measurements without external constraints.

Findings

Spectroscopic gravities agree within 0.01 dex of asteroseismic values.

Spectroscopic gravities agree within 0.06 dex of transit-based values.

Achieved low RMS scatter of 0.05-0.07 dex across a range of stellar parameters.

Abstract

We demonstrate a new procedure to derive accurate and precise surface gravities from high resolution spectra without the use of external constraints. Our analysis utilizes Spectroscopy Made Easy (SME) with robust spectral line constraints and uses an iterative process to mitigate degeneracies in the fitting process. We adopt an updated radiative transfer code, a new treatment for neutral perturber broadening, a line list with multiple gravity constraints and separate fitting for global stellar properties and abundance determinations. To investigate the sources of temperature dependent trends in determining log g noted in previous studies, we obtained Keck HIRES spectra of 42 Kepler asteroseismic stars. In comparison to asteroseismically determined log g our spectroscopic analysis has a constant offset of 0.01 dex with a root mean square (RMS) scatter of 0.05 dex. We also analyzed 30 spectra which had published surface gravities determined using the $a/R_*$ technique from planetary transits and found a constant offset of 0.06 dex and RMS scatter of 0.07 dex. The two samples covered effective temperatures between 5000K and 6700K with log g between 3.7 and 4.6.