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On The Evolution Of...
On The Evolution Of Magnetic White Dwarfs
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Tremblay, P. -E (author)
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- Fontaine, G. (author)
- Univ Montreal, Dept Phys, Montreal, PQ H3C 3J7, Canada.
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- Freytag, Bernd (author)
- Uppsala universitet,Institutionen för fysik och astronomi
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- Steiner, O. (author)
- Kiepenheuer Inst Sonnenphys, D-79104 Freiburg, Germany.;Ist Ric Solari Locarno, CH-6605 Locarno, Switzerland.
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Ludwig, H. -G (author)
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- Steffen, M. (author)
- Leibniz Inst Astrophys Potsdam, D-14482 Potsdam, Germany.
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- Wedemeyer, S. (author)
- Univ Oslo, Inst Theoret Astrophys, NO-0315 Oslo, Norway.
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- Brassard, P. (author)
- Univ Montreal, Dept Phys, Montreal, PQ H3C 3J7, Canada.
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Univ Montreal, Dept Phys, Montreal, PQ H3C 3J7, Canada Institutionen för fysik och astronomi (creator_code:org_t)
- 2015
- 2015
- English.
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In: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 812:1
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Abstract
Subject headings
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- We present the first radiation magnetohydrodynamic simulations of the atmosphere of white dwarf stars. We demonstrate that convective energy transfer is seriously impeded by magnetic fields when the plasma-beta parameter, the thermal-to-magnetic-pressure ratio, becomes smaller than unity. The critical field strength that inhibits convection in the photosphere of white dwarfs is in the range B = 1-50 kG, which is much smaller than the typical 1-1000MG field strengths observed in magnetic white dwarfs, implying that these objects have radiative atmospheres. We have employed evolutionary models to study the cooling process of high-field magnetic white dwarfs, where convection is entirely suppressed during the full evolution (B greater than or similar to 10 MG). We find that the inhibition of convection has no effect on cooling rates until the effective temperature (T-eff) reaches a value of around 5500 K. In this regime, the standard convective sequences start to deviate from the ones without convection due to the convective coupling between the outer layers and the degenerate reservoir of thermal energy. Since no magnetic white dwarfs are currently known at the low temperatures where this coupling significantly changes the evolution, the effects of magnetism on cooling rates are not expected to be observed. This result contrasts with a recent suggestion that magnetic white dwarfs with Teff less than or similar to 10,000 K cool significantly slower than non-magnetic degenerates.
Subject headings
- NATURVETENSKAP -- Fysik -- Astronomi, astrofysik och kosmologi (hsv//swe)
- NATURAL SCIENCES -- Physical Sciences -- Astronomy, Astrophysics and Cosmology (hsv//eng)
Keyword
- convection
- magnetohydrodynamics (MHD)
- stars: evolution
- stars: fundamental parameters
- stars: magnetic field
- white dwarfs
Publication and Content Type
- ref (subject category)
- art (subject category)
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