Something new under the Sun: A magnetically driven CH/CN anti-correlation
Year: 2026
Type: article
Abstract: Context . Spectroscopic monitoring surveys have shown that the magnetic cycle alters the photospheric structure of the Sun, perturbing the formation of molecular lines. In parallel, the study of globular clusters (GCs) has remained centred on the multiple stellar populations (MPs) conundrum, a phenomenon defined – most notably – by the anti-correlation between CH and CN molecular bands, serving to distinguish between first-population (1P) and second-population (2P) stars. Aims . Since these molecular transitions are intrinsically sensitive to photospheric conditions, we investigated whether stellar magnetic activity can induce spectroscopic variations consistent with the signatures traditionally utilised to disentangle 1P and 2P populations. Methods . We bridged the stellar and solar domains by applying standard spectroscopic index analyses – routinely used to identify MPs in clusters – to a decade-long dataset of disc-integrated high-resolution solar spectra. We systematically monitored the behaviour of the CH and CN molecular bands as a function of the solar magnetic cycle. These observational results are further complemented by first-order magnetohydrodynamic (MHD) simulations to evaluate how these signatures scale with increased magnetic activity. Results . We demonstrate that the disc-integrated solar spectrum exhibits a distinct CH/CN anti-correlation driven by the magnetic cycle. Our simulations indicate that these variations in molecular line formation scale significantly with increased magnetic filling factors, rendering them, in principle, capable of reaching amplitudes comparable to the spectroscopic spreads observed between 1P and 2P stars in GCs. Conclusions . While the broader implications of our discovery of a CH/CN anti-correlation in the single-star Sun remain to be fully elucidated, our results suggest that the spectroscopic and photometric anomalies defining the MP conundrum may be physically linked to a differential spectral response to varying degrees of surface magnetic coverage. The emerging mechanism depends on the intrinsic magnetic state of the star – distinguishing relatively active from relatively quiescent stars – rather than the existence of a magnetic cycle itself. Surface magnetism offers a novel physical framework that may provide new insights into the origin of MPs and clearly warrants future exploration.
Source: Astronomy and Astrophysics
Institutions: Osservatorio Astronomico di Padova, National Institute for Astrophysics, Universidad Andrés Bello, Trieste Astronomical Observatory, European Southern Observatory, European Southern Observatory, Université Libre de Bruxelles, University of Padua, Universidade Federal de Viçosa, Osservatorio Astrofisico di Catania, Laboratório Nacional de Astrofísica, Instituto Nacional de Pesquisas Espaciais
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $1,865
OpenAlex ID: W7196933703
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