Simulations of Dynamo Action in Fully Convective Stars

By M. Browning. 2007

279 citations recorded by the source corpus.

We present three-dimensional nonlinear magnetohydrodynamic simulations of the interiors of fully convective M dwarfs. Our models consider 0.3 solar-mass stars using the Anelastic Spherical Harmonic code, with the spherical computational domain extending from 0.08 to 0.96 times the overall stellar radius. Like previous authors, we find that fully convective stars can generate kG-strength magnetic fields (in rough equipartition with the convective flows) without the aid of a tachocline of shear. Although our model stars are everywhere unstably stratified, the amplitudes and typical pattern sizes of the convective flows vary strongly with radius, with the outer regions of the stars hosting vigorous convection and field amplification while the deep interiors are more quiescent. Modest differential rotation is established in hydrodynamic calculations, but—unlike in some prior work—strongly quenched in MHD simulations because of the Maxwell stresses exerted by the dynamo-generated magnetic fields. Despite the lack of strong differential rotation, the magnetic fields realized in the simulations possess significant mean (axisymmetric) components, which we attribute partly to the strong influence of rotation on the slowly overturning flows.

Subfields: Astronomy and Astrophysics, Molecular Biology

View Paper: https://www.semanticscholar.org/paper/7f8bffe820b93304522329ca5e1e6747d69fc271

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In Astronomy and Astrophysics

1. A. Reiners
2. M. Browning
3. D. Charbonneau
4. A. Brun
5. J. Johnson
6. Mark S. Miesch
7. J. Toomre
8. J. Donati

In Molecular Biology

1. M. Browning
2. Mark S. Miesch
3. A. Brun
4. J. Toomre
5. Paul Charbonneau
6. Benjamin P. Brown
7. W. Arnett
8. C. Meakin

Citations in the corpus

• The Habitability of Planets Orbiting M-dwarf Stars (2016, methodology): “Such spectra rely on detailed, computationally intensive modeling of convection in low-mass stellar interiors (Mullan & MacDonald, 2001; Browning, 2008) and complete lists of the complex array of molecules and grains that reside in their atmospheres (Tsuji et al., 1996; Allard et al., 2000).”
• The stellar rotation–activity relationship in fully convective M dwarfs (2018, background): “Later 3D dynamo simulations by Dobler, Stix & Brandenburg (2006) and Browning (2008) were able to generate larger-scale magnetic fields with some evidence that rotation may influence the resulting magnetic field strength.”
• A VOLUME-LIMITED SAMPLE OF 63 M7–M9.5 DWARFS. II. ACTIVITY, MAGNETISM, AND THE FADE OF THE ROTATION-DOMINATED DYNAMO (2009, background): “Our understanding of purely turbulent dynamos is only at its beginning, but large progress was made during the last years (e.g., Durney et al. 1993; Dobler et al. 2006; Browning 2008).”
• Magnetic Fields of Nondegenerate Stars (2009, background): “…(e.g., the presence of an interfac layer or the effect of meridional circulation, Parker 1993; Dikpati & Charbonneau 1999) while direct numerical simulations are now able to reach strongly turbulent regimes capable of producing intense mean magnetic fields (e.g., Brun et al. 2004; Browning 2008).”
• MAGNETIC CYCLES IN A CONVECTIVE DYNAMO SIMULATION OF A YOUNG SOLAR-TYPE STAR (2011, background): “Simulations of dynamo action in fully-convective M-stars do however show high levels of magnetic energy in the mean fields (Browning 2008).”
• Large-scale magnetic topologies of late M dwarfs★: Magnetic topologies of late M dwarfs (2010, background): “Subsequent direct numerical simulations by Dobler et al. (2006) and Browning (2008) both realized large-scale dynamo action with a significant axisymmetric component of the resulting magnetic field.”
• TOWARD REALISTIC PROGENITORS OF CORE-COLLAPSE SUPERNOVAE (2011, methodology): “…(Deupree 1984, 1996, 2003; Dearborn et al. 2006; Moćak et al. 2008, 2009, 2010), and on turbulent MHD with rotation (e.g., M dwarf simulations by Browning 2008), as well as extensive work on the Sun with the ASH code (e.g., Brown et al. 2010) and on stellar atmospheres pioneered by Nordlund…”
• Large-scale magnetic topologies of late M dwarfs⋆ (2008, background): “…of the magnetic field on the star’s internal structure may be associated with the dynamo saturation observed in our sample (see above), and with the frozen differential rotation predicted by Browning (2008) when the magnetic energy reaches equipartition (with respect to the kinetic energy).”
• A CATALOG OF ROTATION AND ACTIVITY IN EARLY-M STARS (2012, background): “…& Basri 2007; Shulyak et al. 2011), Zeeman Doppler imaging of M-stars (Donati et al. 2008; Morin et al. 2008) as well as numerical simulations of magnetic field generation in fully convective stars (Browning 2008) agree that strong magnetic fields exist across the full range of M-type dwarfs.”
• Stellar Flares from the First TESS Data Release: Exploring a New Sample of M Dwarfs (2019, background): “The interaction between rotation and convection can cause high magnetic activity (e.g. Browning 2008), whose energy is then released through flares.”
• METALLICITY AND TEMPERATURE INDICATORS IN M DWARF K-BAND SPECTRA: TESTING NEW AND UPDATED CALIBRATIONS WITH OBSERVATIONS OF 133 SOLAR NEIGHBORHOOD M DWARFS (2011, background): “…parameters have been similarly difficult to achieve: accurately modeling the deep convective zones in M dwarf interiors (Mullan & MacDonald 2001; Browning 2008) and the mixture of molecules – 4 – and grains that dominate M dwarf atmospheres (Tsuji et al. 1996; Allard et al. 2000) requires…”
• Large-scale magnetic topologies of early M dwarfs (2008, background): “Many theoretical models were proposed to attempt resolving this issue (e.g., Durney et al. 1993; Dobler et al. 2006; Browning 2008) but observations of the large-scale magnetic fields at the surfaces of fullyconvective stars, and in particular of their poloidal and toroidal components, are still…”
• PERSISTENT MAGNETIC WREATHS IN A RAPIDLY ROTATING SUN (2010, background): “This view is partly borne out by simulations of Mdwarfs under strong rotational constraints (Browning 2008), where strong longitudinal mean fields were realized despite the lack of either substantial differential rotation or a stble interior and thus no classical tachocline.”