Exoplanets & Exomoons

Towards Characterising Rocky Worlds: Trends In Chemical Make-ups Of M dwarfs Versus GK dwarfs

By Keith Cowing
Status Report
July 9, 2024
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Towards Characterising Rocky Worlds: Trends In Chemical Make-ups Of M dwarfs Versus GK dwarfs
The [Mg/Si]-[C/O] diagram for the M dwarf sample (overlying orange dots) and GK dwarf sample (underlying colourful dots in density). An ODR fit is applied to the M dwarf sample, with the best fit shown in the solid line and 1σ and 2σ error intervals shown in dash and dot lines (in brown), respectively. The regression parameters are also shown on the plot. A Student’s t-test is also applied to test the significance of the slope different from zero, and the resultant p-value is less than 0.001. — astro-ph.SR

Elemental abundances of Sun-like stars are crucial for understanding the detailed properties of their planets. However, measuring elemental abundances in M stars is challenging due to their faintness and pervasive molecular features in optical spectra.

To address this, elemental abundances of Sun-like stars have been proposed to constrain those of M stars by scaling [X/H] with measured [Fe/H]. This study tests the robustness of this practice using M- and GK-dwarf stellar abundances and rigorous statistical methods.

We compile elemental abundances for 43 M dwarfs for 10 major rock-forming elements (Fe, C, O, Mg, Si, Al, Ca, Na, Ni, and Ti) from high-resolution near-infrared stellar surveys. We perform bootstrap-based linear regressions on the M dwarfs to determine the trends of [X/H] vs. [Fe/H] and compare them with GK dwarfs.

A 2-sample, multivariate Mahalanobis Distance test is applied to assess the significance of differences in [X/H]–[Fe/H] trends for individual elemental pairs between M and GK dwarfs. The null hypothesis of no significant difference in chemical trends between M and GK dwarfs is strongly rejected for all elements except Si, for which rejection is marginal, and Na and Ni, for which results are inconclusive.

This suggests that assuming no difference may lead to biased results and inaccurate constraints on rocky planets around M dwarfs. Therefore, it is crucial for both the stellar and exoplanet communities to recognise these differences. To better understand these differences, we advocate for dedicated modelling techniques for M dwarf atmospheres and more homogeneous abundance analyses.

Our statistically constrained trends of [X/H]–[Fe/H] for M dwarfs offer a new constraint on estimating M-dwarf elemental abundances given measured [Fe/H], aiding in characterising the properties of M dwarf-hosted rocky worlds.

Haiyang S. Wang, Sascha P. Quanz, Suvrath Mahadevan, Morgan Deal

Comments: 8 pages, 10 figures, 1 table in the main body; 6 appendices, with 13 figures and an open-access code. Accepted by A&A
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2407.01177 [astro-ph.SR] (or arXiv:2407.01177v1 [astro-ph.SR] for this version)
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Submission history
From: Haiyang Wang
[v1] Mon, 1 Jul 2024 11:01:09 UTC (7,232 KB)

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻