The Composition of M-dwarf Exoplanet Hosts: Atmospheric Parameters and O, Mg, Si, and Fe Abundances from IR Spectroscopy

Determining M-dwarf abundances is an important step to discerning the chemical evolution of the Milky Way and characterizing exoplanetary systems, especially since these objects commonly host small exoplanets. The new analysis still awaits peer review, but it already lays out the central claim clearly.

This matters because exoplanet science has moved beyond the era of simple discovery into a period of comparative characterization. With more than five thousand confirmed planets known, the scientifically productive questions now concern atmospheric composition, internal structure, orbital history and the statistical properties of populations rather than the existence of individual worlds. A new detection or spectral measurement is most valuable when it adds a well-constrained data point to those comparative frameworks, not when it stands alone as an anecdote. However, a dearth of M-dwarf abundance measurements exist compared to Sun-like stars, partially due to their complicated optical spectra dominated by molecular absorption lines. To overcome these issues, we have obtained high resolution H-band spectra of 40 planet-hosting M-dwarf stars and 2 M-dwarfs in wide binaries with FGK primaries with IGRINS on.

Abundances were derived by comparing each observed spectrum to synthetic spectral grids generated with MOOG and MARCS atmospheric models. Effective temperatures were derived using OH and H$_{2}$O lines and from Fe I and FeH lines.

Both Mg and Si abundances were determined using atomic features. Overall, we find that our abundances are broadly consistent with previous literature M-dwarf abundances.

We complemented our abundances analysis with UVW velocities and Milky Way stellar population membership probabilities and identified 2 potential thick disk stars from our. Kinematic stellar population probabilities and a low abundance makes Kepler 42 a likely thick disk star, although uncertain Mg and Si abundances make classification difficult.

The broader interest lies in making the target less anecdotal and more comparable with the rest of the known planetary population. Population-level questions, such as the frequency of atmospheres around small rocky planets or the prevalence of water-rich worlds in the habitable zone, require well-characterized individual data points before statistical patterns become meaningful. Each new planet with a measured radius, mass and, ideally, atmospheric constraint is a brick in that larger structure, and the accumulation of bricks eventually allows theorists to test formation models against real distributions rather than projections.

Lastly, we have determined Si/Mg and Fe/Mg molar ratios for M-dwarf exoplanet hosts and find the abundance distributions leads to exoplanet core-mass fractions between 20 - 40$\%$. Both individuals and organizations that work with arXivLabs have embraced and accepted our values of openness, community, excellence, and user data privacy.

Because this is still a preprint, the result should be read with genuine interest and proportionate caution. Peer review is not a guarantee of correctness, but it is a process that forces authors to respond to technical criticism from specialists who have no stake in a particular outcome. Preprints that survive that process, often with substantive revisions, emerge with a stronger evidential base than the version that first appeared. Until that stage is complete, the responsible reading keeps uncertainty explicitly visible rather than treating the claims as established findings.

The next step is to improve independent constraints on the mass, radius, atmospheric composition and orbital dynamics of the target. Transmission spectroscopy with JWST, radial velocity campaigns with high-resolution ground-based spectrographs and phase-curve measurements from space photometry represent the observational toolkit that can move characterization from plausible to robust. That convergence of techniques is the standard the community now expects before a planetary atmosphere result is treated as confirmed. Until peer review and independent follow-up address those open questions, skepticism is not a failure of appreciation for the work; it is part of how science decides what to keep.

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