Small-scale Dynamo in Cool Stars: I. Changes in stratification and near-surface convection for main-sequence spectral types

Abstract

Some of the small-scale solar magnetic flux can be attributed to a small-scale dynamo (SSD) operating in the near-surface convection. The SSD fields have consequences for solar granular convection, basal flux, as well as chromospheric heating. A similar SSD mechanism is expected to be active in the near-surface convection of other cool main-sequence stars, but this has never been investigated. We aim to investigate changes in stratification and convection due to inclusion of SSD fields for F3V, G2V, K0V and M0V spectral types in the near-surface convection. 3D magnetohydrodynamic (MHD) models of the four stellar boxes, covering the subsurface convection zone up to the lower photosphere in a small cartesian box, are studied using the \textit{MURaM} radiative-MHD simulation code. The SSD runs are compared against reference hydrodynamic runs. An SSD is found to efficiently produce magnetic field with energies ranging between 5\% to 80\% of the plasma kinetic energy at different depths. This ratio tends to be larger for larger $T_{\mathrm{eff}}$. The relative change in density and gas pressure stratification for the deeper convective layers due to SSD magnetic fields is negligible, except for the F-star. For the F-star, there is a substantial reduction in convective velocities due to Lorentz force feedback from magnetic fields, which, in turn, reduces the turbulent pressure. SSD in near-surface convection for cool main-sequence stars introduces small but significant changes in thermodynamic stratification (especially for the F-star) due to reduction in convective velocities.

Update (20.07.2023): an errata (appendix D) has been included to correct a small error in the derivation of turbulent pressure in appendix B. In addition, the text has been updated with the published version. 10 pages, 7 figures, accepted for publication in A&A

References in corpus (12)

• A grid of MARCS model atmospheres for late-type stars I. Methods and general properties
• Modules for Experiments in Stellar Astrophysics (MESA): Pulsating Variable Stars, Rotation, Convective Boundaries, and Energy Conservation
• A Substantial Amount of Hidden Magnetic Energy in the Quiet Sun
• Simulations of nonhelical hydromagnetic turbulence
• Numerical simulations of quiet Sun magnetism: On the contribution from a small-scale dynamo
• A solar surface dynamo
• Extension of the MURaM radiative MHD code for coronal simulations
• Penumbral structure and outflows in simulated sunspots
• Turbulent small-scale dynamo action in solar surface simulations
• Efficient small-scale dynamo in solar convection zone
• Vortex Flow Properties in Simulations of Solar Plage Region: Evidence for their role in chromospheric heating
• 3D hydrodynamical CO5BOLD model atmospheres of red giant stars: I. Atmospheric structure of a giant located near the RGB tip

Cited by in corpus (15)

• Small-scale dynamos: From idealized models to solar and stellar applications
• Can 1D radiative equilibrium models of faculae be used for calculating contamination of transmission spectra?
• Small-scale dynamo in cool main sequence stars. II. The effect of metallicity
• Testing MURaM and MPS-ATLAS against the quiet solar spectrum
• 3D Stagger model atmospheres with FreeEOS I. Exploring the impact of microphysics on the Sun
• Turbulent dynamo action and its effects on the mixing at the convective boundary of an idealized oxygen-burning shell
• Does the ${\nu }_{\max }$ scaling relation depend on metallicity? Insights from 3D convection simulations
• Structure and dynamics of the internetwork solar chromosphere: results of a small-scale dynamo simulation
• Small-scale Dynamo in Cool Stars III. Changes in the photospheres of F3V to M0V stars
• Impacts of small-scale dynamo on rotating columnar convection in stellar convection zones
• Simulations of facular magnetic fields on cool stars I: Main sequence stars with solar metallicity
• 3D Radiative MHD Simulations of Starspots II: Large-scale Structure
• A High-resolution, Inversion-Based Synoptic Study of Solar Granulation
• Solar photospheric spectrum microvariability III. Radial velocities and line profiles in magnetic active-region granulation
• The effect of local magnetic fields in quiet regions of stellar atmospheres simulated with MANCHA