Precision Stellar Characterization of FGKM Stars using an Empirical Spectral Library

TL;DR

This paper introduces a high-resolution spectral library of 404 stars and a new empirical method, SpecMatch-Emp, for accurately determining stellar parameters, especially for late-type stars, using optical spectra.

Contribution

The authors compile a comprehensive spectral library and develop an empirical tool for stellar characterization that improves accuracy for late K-dwarfs and faint stars compared to existing models.

Findings

Spectral library covers M5 to F1 stars with high resolution and SNR.

SpecMatch-Emp achieves 100 K accuracy in Teff and 15% in Rstar for FGKM stars.

Method performs well at lower resolution and SNR, suitable for faint stars.

Abstract

Classification of stars, by comparing their optical spectra to a few dozen spectral standards, has been a workhorse of observational astronomy for more than a century. Here, we extend this technique by compiling a library of optical spectra of 404 touchstone stars observed with Keck/HIRES by the California Planet Search. The spectra are high-resolution (R~60000), high signal-to-noise (SNR~150/pixel), and registered onto a common wavelength scale. The library stars have properties derived from interferometry, asteroseismology, LTE spectral synthesis, and spectrophotometry. To address a lack of well-characterized late K-dwarfs in the literature, we measure stellar radii and temperatures for 23 nearby K-dwarfs, using SED modeling and Gaia parallaxes. This library represents a uniform dataset spanning the spectral types ~M5--F1 (Teff ~ 3000-7000K, Rstar ~ 0.1-1.6 Rsun). We also present "Empirical SpecMatch" (SpecMatch-Emp), a tool for parameterizing unknown spectra by comparing them against our spectral library. For FGKM stars, SpecMatch-Emp achieves accuracies of 100 K in effective temperature (Teff), 15% in stellar radius (Rstar), and 0.09 dex in metallicity [Fe/H]. Because the code relies on empirical spectra it performs particularly well for stars ~K4 and later which are challenging to model with existing spectral synthesizers, reaching accuracies of 70 K in Teff, 10% in Rstar, and 0.12 dex in [Fe/H]. We also validate the performance of SpecMatch-Emp, finding it to be robust at lower spectral resolution and SNR, enabling the characterization of faint late-type stars. Both the library and stellar characterization code are publicly available.