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Federico Spada (MPS)

An improved calibration for the radii of cool stars
When Sep 27, 2018 from 02:30 PM to 03:30 PM
  • Colloquium
Where SH Lecture Hall
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Main sequence, solar-like stars (M < 1.3 Msun) have outer convective envelopes that are sufficiently thick to affect their overall structure and global parameters. In particular, their surface radii are sensitive to the details of inefficient, sub-adiabatic convection, which are poorly described by the Mixing Length Theory (MLT), the standard treatment of convection adopted in stellar evolution codes. The MLT also introduces a free parameter whose calibration and dependence on the current stellar properties and its previous history are left completely unspecified by the theory.

I will discuss an improved calibration of the MLT parameter based on three-dimensional radiation hydrodynamics (3D RHD) simulations of convection. In this approach, the MLT parameter is adjusted to match the specific entropy in the deep, adiabatic layers of the convective envelope to the corresponding value obtained from the 3D RHD simulations. This entropy-based calibration takes into account the position of the star in the (log g, log Teff) plane and its chemical composition. Models of the present-day Sun constructed using the entropy-based calibration, as well as their properties and revised past and future evolution in comparison with the results of the standard solar model calibration will be discussed.