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arXiv · 2611.05740

The impact of M dwarf stellar convection on exoplanetary atmospheric signatures. A 3D radiation-hydrodynamics simulation analysis for high-resolution spectroscopy

A. Chiavassa·M. Brogi·T. Masseron·R. Van den Broeck·L. Bigot·V. Parmentier
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Abstract

M dwarf stars represent prime targets for the detection and characterization of small, temperate exoplanets; however, their complex activity and convective surfaces pose significant challenges for high-resolution spectroscopic studies. This work aims to investigate the impact of stellar convection on high-resolution spectroscopic observations of M dwarf stars and develop an integrated approach combining 3D radiative hydrodynamical simulations, spectroscopic modeling, and transit analysis to mitigate stellar noise. We employ 3D radiative hydrodynamical simulations of M dwarf stellar convection to generate synthetic spectra. We compare the synthetic spectra to actual observations of GJ 3470. We model a high-resolution transit sequence of the Neptune-size GJ 3470 b, including centre-to-limb variations (CLVs) and the Rossiter-McLaughlin effect (RME), and process the sequence via principal component analysis (PCA) to de-trend stellar effects. Comparison of synthetic spectra with actual observations shows that current H2O line lists remain inaccurate, with modest agreement in line strength and position for the chosen K-band interval. During the transit of GJ 3470 b, the amplitude of CLVs+RME is comparable to exoplanet signals. Current PCA can in principle de-trend such effects, but its behaviour is highly dependent on the copresence of telluric and planetary signals. While we are able to correctly detect the exoplanet with no evident bias from stellar residuals, this result is limited to a narrow spectral interval and a specific orbital configuration. This study demonstrates that 3D radiative hydrodynamical simulations are essential for accurately modeling convection-induced spectral variability in M dwarfs. Our integrated framework establishes a foundation to obtain unbiased measurements from future ELT observations of exoplanets orbiting M dwarfs.

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A. Chiavassa, M. Brogi, T. Masseron, R. Van den Broeck, L. Bigot, V. Parmentier. 2026-11-03. The impact of M dwarf stellar convection on exoplanetary atmospheric signatures. A 3D radiation-hydrodynamics simulation analysis for high-resolution spectroscopy. https://arxiv.org/abs/2611.05740

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