Energy Transport, Overshoot, and Mixing in the Atmospheres of Very Cool Stars

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Abstract

We constructed hydrodynamical model atmospheres for mid M-type main-, as well as pre-main-sequence objects. Despite the complex chemistry encountered in such cool atmospheres a reasonably accurate representation of the radiative transfer is possible. The detailed treatment of the interplay between radiation and convection in the hydrodynamical models allows to study processes usually not accessible within the framework conventional model atmospheres. In particular, we determined the efficiency of the convective energy transport, and the efficiency of mixing by convective overshoot. The convective transport efficiency expressed in terms of an equivalent mixing-length parameter amounts to values around 2 in the optically thick, and 2.8 in the optically thin regime. The thermal structure of the formally convectively stable layers is little affected by convective overshoot and wave heating, i.e. stays close to radiative equilibrium. Mixing by convective overshoot shows an exponential decline with geometrical distance from the Schwarzschild stability boundary. The scale height of the decline varies with gravitational acceleration roughly as g(-1/2), with 0.5 pressure scale heights at log(g)=5.0.

Detaljer

Författare
  • Hans-Günter Ludwig
Enheter & grupper
Forskningsområden

Ämnesklassifikation (UKÄ) – OBLIGATORISK

  • Astronomi, astrofysik och kosmologi
Originalspråkengelska
Titel på värdpublikationModelling of Stellar Atmospheres ; Proceedings of the 210th Symposium of the International Astronomical Union held at Uppsala University, Uppsala, Sweden, 17-21 June, 2002
RedaktörerN. Piskunov, W.W. Weiss, D.F. Gray
FörlagAstronomical Society of the Pacific (ASP)
Sidor113-125
Volym210
ISBN (tryckt)1-583-81160-5
StatusPublished - 2003
PublikationskategoriForskning
Peer review utfördJa

Publikationsserier

Namn
Volym210