10:00 〜 10:15
[PEM14-04] Mean-field study of stellar activity-rotation relationship
This study explores the relationship between stellar surface magnetic fields and rotation rates. Previous observations (e.g., Wright+ 2011, 2018) have established a connection between stellar activity and rotation rates, with recent observations by Reiners (2022) indicating a parallel trend in surface magnetic fields. Observations suggest an anti-correlation between the magnetic field and Ro within the moderate Ro range (0.1 < Ro < 1), reaching saturation at extremely low Ro.
Here, the Rossby number (Ro) is a crucial measure in assessing the impact of rotation on dynamics defined as the rotation period over convective turnover time.
While global magnetohydrodynamic (MHD) simulations, such as those by Brun+ (2022), successfully replicate the anticorrelation in moderate Ro, the saturation phenomenon at extremely low Ro remains beyond the reach of current global simulations, and its driving mechanism remains unclear.
To elucidate the saturation of the stellar magnetic field at extremely low Ro, We perform non-kinematic mean-field dynamo simulations by extending the solar case by Rempel (2006). Our findings reveal that the magnetic field strength is influenced by both stellar rotation rates and the assumed turbulent angular momentum (AM) transport process. Through detailed analysis, we demonstrate that the dependence of the magnetic field on Ro is intricately determined by the balance between AM transport by turbulence and the magnetic field.
Notably, our results, in conjunction with recent insights into turbulence properties at low Ro (e.g. Kapyla+ 2023), align closely with observed magnetic field saturation patterns reported by Reiners (2022).
This work contributes to a deeper understanding of the mechanisms governing stellar magnetic field behavior, particularly in the challenging regime of extremely low Rossby numbers.
Here, the Rossby number (Ro) is a crucial measure in assessing the impact of rotation on dynamics defined as the rotation period over convective turnover time.
While global magnetohydrodynamic (MHD) simulations, such as those by Brun+ (2022), successfully replicate the anticorrelation in moderate Ro, the saturation phenomenon at extremely low Ro remains beyond the reach of current global simulations, and its driving mechanism remains unclear.
To elucidate the saturation of the stellar magnetic field at extremely low Ro, We perform non-kinematic mean-field dynamo simulations by extending the solar case by Rempel (2006). Our findings reveal that the magnetic field strength is influenced by both stellar rotation rates and the assumed turbulent angular momentum (AM) transport process. Through detailed analysis, we demonstrate that the dependence of the magnetic field on Ro is intricately determined by the balance between AM transport by turbulence and the magnetic field.
Notably, our results, in conjunction with recent insights into turbulence properties at low Ro (e.g. Kapyla+ 2023), align closely with observed magnetic field saturation patterns reported by Reiners (2022).
This work contributes to a deeper understanding of the mechanisms governing stellar magnetic field behavior, particularly in the challenging regime of extremely low Rossby numbers.