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Numerical simulations of surface convection in a late M-dwarf

Ludwig, Hans-Günter LU ; Allard, F. and Hauschildt, P. H. (2002) In Astronomy & Astrophysics 395(1). p.99-115
Abstract
Based on detailed 2D and 3D numerical radiation-hydrodynamics (RHD)simulations of time-dependent compressible convection, we have studiedthe dynamics and thermal structure of the convective surface layers of aprototypical late-type M-dwarf (T<SUB>eff</SUB>approx 2800 K, log g=5.0,solar chemical composition). The RHD models predict stellar granulationqualitatively similar to the familiar solar pattern. Quantitatively, thegranular cells show a convective turn-over time scale of ~100 s, and ahorizontal scale of 80 km; the relative intensity contrast of thegranular pattern amounts to 1.1%, and root-mean-square verticalvelocities reach 240 m s<SUP>-1</SUP> at maximum. Deviations fromradiative equilibrium in the higher,... (More)
Based on detailed 2D and 3D numerical radiation-hydrodynamics (RHD)simulations of time-dependent compressible convection, we have studiedthe dynamics and thermal structure of the convective surface layers of aprototypical late-type M-dwarf (T<SUB>eff</SUB>approx 2800 K, log g=5.0,solar chemical composition). The RHD models predict stellar granulationqualitatively similar to the familiar solar pattern. Quantitatively, thegranular cells show a convective turn-over time scale of ~100 s, and ahorizontal scale of 80 km; the relative intensity contrast of thegranular pattern amounts to 1.1%, and root-mean-square verticalvelocities reach 240 m s<SUP>-1</SUP> at maximum. Deviations fromradiative equilibrium in the higher, formally convectively stableatmospheric layers are found to be insignificant allowing a reliablemodeling of the atmosphere with 1D standard model atmospheres. Amixing-length parameter of alpha<SUB>MLT = 2.1</SUB> provides the bestrepresentation of the average thermal structure of the RHD modelatmosphere while alternative values are found when fitting theasymptotic entropy encountered in deeper layers of the stellar envelope(alpha<SUB>MLT = 1.5</SUB>), or when matching the vertical velocity(alpha<SUB>MLT = 3.5</SUB>). The close correspondence between RHD andstandard model atmospheres implies that presently existing discrepanciesbetween observed and predicted stellar colors in the M-dwarf regimecannot be traced back to an inadequate treatment of convection in the 1Dstandard models. The RHD models predict a modest extension of theconvectively mixed region beyond the formal Schwarzschild stabilityboundary which provides hints for the distribution of dust grains incooler (brown dwarf) atmospheres. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
convection, hydrodynamics, radiative transfer, stars: atmospheres, stars: late-type
in
Astronomy & Astrophysics
volume
395
issue
1
pages
99 - 115
publisher
EDP Sciences
external identifiers
  • wos:000179048000015
  • scopus:0036851968
ISSN
0004-6361
DOI
10.1051/0004-6361:20021153
language
English
LU publication?
yes
id
566e1efc-5822-406b-8af5-49867d5e5123 (old id 130322)
date added to LUP
2007-07-13 14:02:04
date last changed
2017-11-05 04:35:21
@article{566e1efc-5822-406b-8af5-49867d5e5123,
  abstract     = {Based on detailed 2D and 3D numerical radiation-hydrodynamics (RHD)simulations of time-dependent compressible convection, we have studiedthe dynamics and thermal structure of the convective surface layers of aprototypical late-type M-dwarf (T&lt;SUB&gt;eff&lt;/SUB&gt;approx 2800 K, log g=5.0,solar chemical composition). The RHD models predict stellar granulationqualitatively similar to the familiar solar pattern. Quantitatively, thegranular cells show a convective turn-over time scale of ~100 s, and ahorizontal scale of 80 km; the relative intensity contrast of thegranular pattern amounts to 1.1%, and root-mean-square verticalvelocities reach 240 m s&lt;SUP&gt;-1&lt;/SUP&gt; at maximum. Deviations fromradiative equilibrium in the higher, formally convectively stableatmospheric layers are found to be insignificant allowing a reliablemodeling of the atmosphere with 1D standard model atmospheres. Amixing-length parameter of alpha&lt;SUB&gt;MLT = 2.1&lt;/SUB&gt; provides the bestrepresentation of the average thermal structure of the RHD modelatmosphere while alternative values are found when fitting theasymptotic entropy encountered in deeper layers of the stellar envelope(alpha&lt;SUB&gt;MLT = 1.5&lt;/SUB&gt;), or when matching the vertical velocity(alpha&lt;SUB&gt;MLT = 3.5&lt;/SUB&gt;). The close correspondence between RHD andstandard model atmospheres implies that presently existing discrepanciesbetween observed and predicted stellar colors in the M-dwarf regimecannot be traced back to an inadequate treatment of convection in the 1Dstandard models. The RHD models predict a modest extension of theconvectively mixed region beyond the formal Schwarzschild stabilityboundary which provides hints for the distribution of dust grains incooler (brown dwarf) atmospheres.},
  author       = {Ludwig, Hans-Günter and Allard, F. and Hauschildt, P. H.},
  issn         = {0004-6361},
  keyword      = {convection,hydrodynamics,radiative transfer,stars: atmospheres,stars: late-type},
  language     = {eng},
  number       = {1},
  pages        = {99--115},
  publisher    = {EDP Sciences},
  series       = {Astronomy & Astrophysics},
  title        = {Numerical simulations of surface convection in a late M-dwarf},
  url          = {http://dx.doi.org/10.1051/0004-6361:20021153},
  volume       = {395},
  year         = {2002},
}