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- Dorch, S B F, et al.
(författare)
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Small-scale magnetic fields on late-type M-dwarfs
- 2002
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Ingår i: Astronomical Notes - Astronomische Nachrichten. - 0004-6337. ; 323:3-4, s. 402-406
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Tidskriftsartikel (refereegranskat)abstract
- We performed kinematic studies of the evolution of small-scale magneticfields in the surface layers of M-dwarfs. We solved the inductionequation for a prescribed velocity field, magnetic Reynolds number ReM,and boundary conditions in a Cartesian box, representing a volumecomprising the optically thin stellar atmosphere and the uppermost partof the optically thick convective envelope. The velocity field isspatially and temporally variable, and stems from detailedradiation-hydrodynamics simulations of convective flows in aproto-typical late-type M-dwarf (Teff =2800pun {K}, logg =5.0, solarchemical composition, spectral type ~M6). We find dynamo action for ReM>= 400. Growth time scales of the magnetic field are comparable tothe convective turn-over time scale (~ 150pun {sec}). The convectivevelocity field concentrates the magnetic field in sheets and tubularstructures in the inter-granular downflows. Scaling from solarconditions suggests that field strengths as high as 20pun{kG} might bereached locally. Perhaps surprisingly, ReM is of order unity in thesurface layers of cooler M-dwarfs, rendering the dynamo inoperative. Inall studied cases we find a rather low spatial filling factor of themagnetic field.
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| 2. |
- Wedemeyer, S., et al.
(författare)
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3-D hydrodynamic simulations of the solar chromosphere
- 2003
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Ingår i: Astronomical Notes - Astronomische Nachrichten. - : Wiley. - 0004-6337 .- 1521-3994. ; 324:4, s. 410-411
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Tidskriftsartikel (refereegranskat)abstract
- We present first results of three-dimensional numerical simulations ofthe non-magnetic solar chromosphere, computed with the radiationhydrodynamics code CO5BOLD. Acoustic waves which are excitedat the top of the convection zone propagate upwards into thechromosphere where the waves steepen into shocks. The interaction of thewaves leads to the formation of complex structures which evolve on shorttime scales. Consequently, the model chromosphere is highly dynamical,inhomogeneous, and thermally bifurcated.
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| 3. |
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