Publisher：Nature Astronomy  

For more than 45 years, scientists have believed in the existence of two classes of differential rotation (DR): solar-like and anti-solar. The Sun rotates differentially with a fast equator and slow poles, called solar-like DR. Theoretical studies suggest that this DR becomes anti-solar in slowly rotating stars, where the poles rotate faster. The DR topology substantially affects the stellar magnetic activity and long-time stellar evolution. According to recently reported observations, however, there are some indications that challenge this solar-like and anti-solar picture in several aspects. We carry out unprecedentedly high-resolution magnetohydrodynamic simulations for the slowly rotating solar-type stars. The simulated solar-type stars consistently exhibit solar-like DR even at remarkably slow rotation rates in our simulations. While anti-solar DR has been predicted in previous models, we do not observe it under the conditions explored here. The strong magnetic field maintains the solar-like DR in all cases. The rotation has a less substantial influence on the magnetic field strength than that on the turbulence anisotropy. Our results show that the magnetic field monotonically decreases over the stellar lifetime, indicating a weakening of the magnetic braking. This trend is also consistent with recent observational results of the stellar rotation evolution. Taken together, this work revises the conventional picture of DR in slowly rotating stars and highlights magnetism as a key ingredient in stellar rotational and magnetic evolution.

DOI： 10.1038/s41550-026-02793-x

Open Access

Web of Science

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.3847/1538-4357/ae260b

Open Access

Publisher：Astrophysical Journal  

We have carried out inversions of travel times as measured by Gizon et al. to infer the internal profile of the solar meridional circulation (MC). A linear inverse problem has been solved by the regularized least-squares method with a constraint that the angular momentum (AM) transport by MC should be equatorward (HK21-type constraint). Our motivation for using this constraint is based on the result by Hotta & Kusano (hereafter HK21), where the solar equator-fast rotation was reproduced successfully without any manipulation. The inversion result indicates that the MC profile is a double-cell structure if the so-called HK21 regime, in which AM transported by MC sustains the equator-fast rotation, correctly describes the physics inside the solar convective zone. The sum of the squared residuals computed with the inferred double-cell MC profile is comparable to that computed with the single-cell MC profile obtained when we exclude the HK21-type constraint, showing that both profiles can explain the data more or less at the same level. However, we also find that adding the HK21-type constraint degrades the resolution of the averaging kernels. Although it is difficult for us to determine the large-scale morphology of the solar MC at the moment, our attempt highlights the relevance of investigating the solar MC profile from both theoretical and observational perspectives.

DOI： 10.3847/1538-4357/ad596c

Open Access

Web of Science

Scopus

Publisher：Astrophysical Journal  

To decipher complex patterns of gravity-mode period spacings observed for intermediate-mass main-sequence stars is an important step toward a better understanding of the structure and dynamics in the deep radiative region of the stars. In this study, we apply the JWKB approximation to derive a semi-analytical expression of the g-mode period spacing pattern, for which the gradient in the Brunt-Väisälä frequency is taken into account. The formulation includes the term P ⁻¹ B <inf>⋆</inf>, where P and B <inf>⋆</inf> represent the g-mode period and degree of the structural variation, the latter of which especially is related to the steepness of the gradient of the Brunt-Väisälä frequency. Tests with one-dimensional stellar models show that the semi-analytical expression derived in this study is useful for inferring the degree of the structural variation B <inf>⋆</inf> with an accuracy of ∼10 % in the case of relatively massive intermediate-mass models with the mass M larger than 3 M <inf>⊙</inf>. The newly formulated expression will possibly allow us to put further constraints on, e.g., mixing processes inside intermediate-mass main-sequence g-mode pulsators such as β Cep, SPB, and γ Dor stars that have been principal targets in asteroseismology.

DOI： 10.3847/1538-4357/acd4b9

Open Access

Web of Science

Scopus