![Example fits to the observed spectrum of GJ 436 (Teff = 3495 K, [Fe/H] = -0.05 dex, 2023 observation), LHS 1140 (Teff = 3111 K, [Fe/H] = β0.07 dex), and TOI 2290 (Teff = 3758 K, [Fe/H] = β0.18 dex) are shown as solid purple, gold, and cyan points, respectively. GJ 436 and LHS 1140 spectra were obtained with IGRINS while the TOI 2290 spectrum was obtained with NIRSPEC. The FeH line falls in an order gap for our NIRSPEC spectra and is not shown in this figure. Best fitting synthetic spectra are shown as dashed lines. Synthetic spectra creation and fitting methodology is described in section 3.-- [astro-ph.SR]](https://i0.wp.com/astrobiology.com/wp-content/uploads/2026/11/The-Composition.png?fit=1200%2C705&ssl=1)
[astro-ph.SR] 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.
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 and low luminosities.
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 Gemini South and on the McDonald Observatory 2.7m telescope, and NIRSPEC on Keck. 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 H2O lines and [Fe/H] 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 and chemical analysis: GJ 1252 and L181-1 which was a previously known thick disk star. Kinematic stellar population probabilities and a low [Fe/H] abundance makes Kepler 42 a likely thick disk star, although uncertain Mg and Si abundances make classification difficult.
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%.
Zachary G Maas, Natalie R. Hinkel, Gregory N. Mace, Cayman T. Unterborn, Catherine Pilachowski, Christopher Sneden, Isabella Flores, Joseph G. Schulze
Comments: 23 pages, 11 figures, accepted for publication in The Astrophysical Journal
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2611.07037 [astro-ph.SR] (or arXiv:2611.07037v1 [astro-ph.SR] for this version)
https://doi.org/10.48550/arXiv.2611.07037
Focus to learn more
Submission history
From: Zachary Maas
[v1] Wed, 4 Nov 2026 19:01:46 UTC (1,612 KB)
https://arxiv.org/abs/2611.07037
Astrobiology, exoplanet,
