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arXiv · 2509.03276

Stellar-activity analysis of the nearby M dwarf GJ 526. Multi-dimensional Gaussian-process modelling of RV, FWHM and S-index

A. K. Stefanov·J. I. González Hernández·A. Suárez Mascareño·R. Rebolo·N. Nari·J. M. Mestre·S. G. Sousa·H. M. Tabernero·M. -R. Zapatero Osorio·P. Figueira·J. P. Faria·M. J. Hobson·A. M. Silva·A. Castro-González·N. C. Santos·A. Sozzetti·F. Pepe·S. Cristiani·B. Lavie·C. J. A. P. Martins
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Abstract

M dwarfs are the most abundant stars in the Galaxy, and their low masses make them natural favourites for exoplanet radial-velocity (RV) searches. Nevertheless, these stars often demonstrate strong stellar activity that is yet to be fully understood. We use high-precision ESPRESSO, HIRES, and HARPS spectroscopy to perform a stellar-activity analysis on the nearby early M dwarf GJ 526 ($d=5.4$ pc). We carry out joint modelling of: (i) stellar rotation in RV, FWHM, and Mount Wilson S-index through Gaussian processes, (ii) long-term trends in these three physical quantities, (iii) RV planetary signals. We constrain the stellar-rotation period to $P_\text{rot}=48.7\pm 0.3$ d, and discover a weak sinusoidal signature in RV, FWHM and S-index of period $P_\text{cyc}=1680^{+50}_{-40}$ d. We propose phase-space trajectories between RV and activity indicators as a novel means to visualise and interpret stellar activity. Current evidence does not support planetary companions of GJ 526.

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A. K. Stefanov, J. I. González Hernández, A. Suárez Mascareño, R. Rebolo, N. Nari, J. M. Mestre, S. G. Sousa, H. M. Tabernero, M. -R. Zapatero Osorio, P. Figueira, J. P. Faria, M. J. Hobson, A. M. Silva, A. Castro-González, N. C. Santos, A. Sozzetti, F. Pepe, S. Cristiani, B. Lavie, C. J. A. P. Martins. 2025-09-03. Stellar-activity analysis of the nearby M dwarf GJ 526. Multi-dimensional Gaussian-process modelling of RV, FWHM and S-index. https://doi.org/10.1051/0004-6361%2F202556346

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