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Small-scale magnetic fields on late-type M-dwarfs

Dorch, S B F and Ludwig, Hans-Günter LU (2002) In Astronomical Notes - Astronomische Nachrichten 323(3-4). p.402-406
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... (More)
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. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
stars: activity, stars: low-mass, stars: magnetic fields
in
Astronomical Notes - Astronomische Nachrichten
volume
323
issue
3-4
pages
402 - 406
publisher
John Wiley & Sons
external identifiers
  • wos:000177865100044
  • scopus:0036398779
ISSN
0004-6337
DOI
10.1002/1521-3994(200208)323:3/4<402::AID-ASNA402>3.0.CO;2-H
language
English
LU publication?
yes
id
aebaf2d5-ff18-44a5-a139-a661698cf173 (old id 130338)
date added to LUP
2007-07-12 15:58:01
date last changed
2017-01-01 05:10:33
@article{aebaf2d5-ff18-44a5-a139-a661698cf173,
  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&gt;= 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.},
  author       = {Dorch, S B F and Ludwig, Hans-Günter},
  issn         = {0004-6337},
  keyword      = {stars: activity,stars: low-mass,stars: magnetic fields},
  language     = {eng},
  number       = {3-4},
  pages        = {402--406},
  publisher    = {John Wiley & Sons},
  series       = {Astronomical Notes - Astronomische Nachrichten},
  title        = {Small-scale magnetic fields on late-type M-dwarfs},
  url          = {http://dx.doi.org/10.1002/1521-3994(200208)323:3/4<402::AID-ASNA402>3.0.CO;2-H},
  volume       = {323},
  year         = {2002},
}