Hejazi, NedaJ. M. Crossfield, IanNordlander, ThomasMansfield, MeganSouto, DiogoMarfil, EmilioR. Coria, DavidBrande, JonathanS. Polanski, AlexE. Hand, JosephF. Wienke, Kate2025-03-102025-03-100004-637Xhttps://hdl.handle.net/1885/733737843We present the first elemental abundance measurements of the K dwarf (K7V) exoplanet-host star WASP-107 using high-resolution (R ≃45,000), near-infrared (H- and K-band) spectra taken from Gemini-S/IGRINS. We use the previously determined physical parameters of the star from the literature and infer the abundances of 15 elements—C, N, O, Na, Mg, Al, Si, K, Ca, Ti, V, Cr, Mn, Fe, and Ni, all with precision < 0.1 dex—based on model fitting using MARCS model atmospheres and the Turbospectrum spectral synthesis code. Our results show near-solar abundances and a carbon-to-oxygen ratio (C/O) of 0.50 ± 0.10, which is consistent with the solar value of 0.54 ± 0.09. The orbiting planet, WASP-107b, is a super-Neptune with a mass in the Neptune regime (=1.8 MNep) and a radius close to Jupiter's (=0.94 RJup). This planet is also being targeted by four JWST Cycle 1 programs in transit and eclipse, which should provide highly precise measurements of atmospheric abundances. This will enable us to properly compare the planetary and stellar chemical abundances, which is essential in understanding the formation mechanisms, internal structure, and chemical composition of exoplanets. Our study is a proof-of-concept that will pave the way for such measurements to be made for all of JWST's cooler exoplanet-host stars.N.H. and I.J.M.C. acknowledge support from NSF AAG grant No. 2108686 and from NASA ICAR grant No. NNH19ZDA001N. T.N. acknowledges support from the Australian Research Council Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), through project No. CE170100013. D.S. thanks the National Council for Scientific and Technological DevelopmentCNPq. E.M. acknowledges financial support through a "Margarita Salas" postdoctoral fellowship from Universidad Complutense de Madrid (CT18/22), funded by the Spanish Ministerio de Universidades with NextGeneration EU funds.application/pdfen-AU©2023 The authorshttp://creativecommons.org/licenses/by/4.0/202310.3847/1538-4357/accb972023-12-24Creative Commons Attribution licence