Expanding the Volatile Abundance Inventory for High-Priority K-Dwarf JWST Exoplanet Systems

Abstract

There are exceedingly few chemical abundance measurements available in the literature for K dwarf stars, especially for those with T$_{eff} <$ 4700 K due to an incompatibility of traditional analyses with their molecular-line-ridden optical spectra. To address the need for K dwarf abundance constraints, we present an elemental ([C/H], [O/H]) and isotopic ($^{12}$C/$^{13}$C, $^{16}$O/$^{18}$O) abundance analysis for six K dwarf exoplanet host stars: K2-141, NGTS-10, WASP-43, WASP-69, WASP-80, and HATS-72. Each system hosts an exoplanet targeted by JWST characterization efforts, making host star abundances especially critical as baseline references. Using MARCS model atmospheres, the TurboSpectrum spectral synthesis code, and near-infrared IGRINS spectra, we derive novel [C/H] and [O/H] abundance ratios for these high-priority K dwarf host stars. We further investigate prospects for determining $^{12}$C/$^{13}$C and $^{16}$O/$^{18}$O ratios using $^{13}$C$^{16}$O and $^{12}$C$^{18}$O lines from the 2.3 micron CO bandhead. The observed spectra are too noisy to measure $^{16}$O/$^{18}$O ratios for the sample, but we do find sub-solar $^{12}$C/$^{13}$C ratios for five out of six targets. We also derive uniform gyrochronological ages for each host star to compare with galactic chemical evolution models and identify underlying abundance-age trends. NIR H+K band spectroscopy provides an alternative to optical, atomic line-derived carbon and oxygen abundances for cool dwarf stars. The growing catalog of precise host star elemental and isotopic abundances complements ongoing observations of their companions and provides a baseline for understanding their chemical composition, origin, and evolution.