Volume 586, February 2016
|Number of page(s)||6|
|Section||Stellar structure and evolution|
|Published online||28 January 2016|
Scaling of the asymptotic entropy jump in the superadiabatic layers of stellar atmospheres
1 Niels Bohr Institute, University of Copenhagen Juliane Maries Vej 30 2100 Copenhagen Denmark
2 Centre for Star and Planet Formation, Natural History Museum of Denmark, Øster Voldgade 5–7, 1350 Copenhagen, Denmark
Received: 23 September 2015
Accepted: 3 December 2015
Context. Stellar structure calculations are able to predict precisely the properties of stars during their evolution. However, convection is still modelled by the mixing length theory; therefore, the upper boundary conditions near the optical surface do not agree with asteroseismic observations.
Aims. We want to improve how the outer boundary conditions are determined in stellar structure calculations.
Methods. We study realistic 3D stellar atmosphere models to find alternative properties.
Results. We find that the asymptotic entropy run of the superadiabatic convective surface layers exhibit a distinct universal stratification when normalized by the entropy minimum and jump.
Conclusions. The normalized entropy can be represented by a 5th order polynomial very accurately, and a 3rd order polynomial also yields accurate coefficients. This generic entropy stratification or the solar stratification, when scaled by the entropy jump and minimum, can be used to improve the modelling of superadiabatic surface layers in stellar structure calculations. Furthermore, this finding indicates that surface convection operates in the same way for all cool stars, but requires further scrutiny in order to improve our understanding of stellar atmospheres.
Key words: convection / hydrodynamics / radiative transfer / stars: atmospheres / stars: evolution / asteroseismology
© ESO, 2016
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