Stellar Characterization and Chemical Abundances of Exoplanet-hosting M Dwarfs from APOGEE Spectra: Future JWST Targets
Edypo Melo, Diogo Souto, Kátia Cunha, Verne V. Smith, Fábio Wanderley, Vinicius Grilo, Deusalete Camara, Kely Murta, Neda Hejazi, Ian J. M. Crossfield, Johanna Teske, R. Luque, Michael Zhang, Jacob L. Bean
Abstract
Abstract Exoplanets hosting M dwarfs are the best targets to characterize Earth-like or super-Earth planetary atmospheres with the James Webb Space Telescope (JWST). We determine detailed stellar parameters ( T eff , log g , and ξ ) and individual abundances of 12 elements for four cool M dwarfs hosting exoplanets TOI-1685, GJ 436, GJ 3470, and TOI-2445, scheduled for future observations by the JWST. The analysis utilizes high-resolution near-infrared spectra from the Sloan Digital Sky Survey IV APOGEE survey between 1.51 and 1.69 μ m. Based on 1D LTE plane-parallel models, we find that TOI-2445 is slightly metal poor ([Fe/H] = −0.16 ± 0.09 dex), while TOI-1685, GJ 436, and GJ 3470 are more metal rich ([Fe/H] = 0.06 ± 0.18, 0.10 ± 0.20, and 0.25 ± 0.15 dex, respectively). The derived C/O ratios for TOI-2445, TOI-1685, GJ 436, and GJ 3470 are 0.526 ± 0.027, 0.558 ± 0.097, 0.561 ± 0.029, and 0.638 ± 0.015, respectively. From the results for 28 M dwarfs analyzed homogeneously from Apache Point Observatory Galactic Evolution Experiment (APOGEE) spectra, we find exoplanet-hosting M dwarfs exhibit a C/O abundance ratio approximately 0.01–0.05 higher than those with nondetected exoplanets, at limits of a statistically significant offset. A linear regression of the [Fe/H] versus C/O distribution reveals a noticeable difference in the angular coefficient between FGK dwarfs (0.27) and M dwarfs (0.13). Assuming our abundance ratios of Ca/Mg, Si/Mg, Al/Mg, and Fe/Mg, we determine a mass of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>3.276</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.419</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.448</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> M ⊕ for TOI-2445 b, which has a density (6.793 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow/> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.099</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.005</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> g cm −3 ) and core mass fraction (0.329 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow/> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.049</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.028</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> ) very similar to Earth’s. We also present an atlas of 113 well-defined spectral lines to analyze M dwarfs in the H band and a comprehensive evaluation of uncertainties from variations in the atmospheric parameters, signal-to-noise ratio, and pseudocontinuum.