Kavli Affiliate: Lars Bildsten
| First 5 Authors: Jared A. Goldberg, Yan-Fei Jiang, Lars Bildsten, ,
| Summary:
We explore the three-dimensional properties of convective, luminous
($Lapprox10^{4.5}-10^{5}L_odot$), Hydrogen-rich envelopes of Red Supergiants
(RSGs) based on radiation hydrodynamic simulations in spherical geometry using
$texttt{Athena++}$. These computations comprise $approx30%$ of the stellar
volume, include gas and radiation pressure, and self-consistently track the
gravitational potential for the outer $approx 3M_odot$ of the simulated
$Mapprox15M_odot$ stars. This work reveals a radius, $R_mathrm{corr}$,
around which the nature of the convection changes. For $r>R_mathrm{corr}$,
though still optically thick, diffusion of photons dominates the energy
transport. Such a regime is well-studied in less luminous stars, but in RSGs,
the near- (or above-) Eddington luminosity (due to opacity enhancements at
ionization transitions) leads to the unusual outcome of denser regions moving
outwards rather than inward. This region of the star also has a large amount of
turbulent pressure, yielding a density structure much more extended than 1D
stellar evolution predicts. This "halo" of material will impact predictions for
both shock breakout and early lightcurves of Type II-P supernovae. Inside of
$R_mathrm{corr}$, we find a nearly flat entropy profile as expected in the
efficient regime of mixing-length-theory (MLT). Radiation pressure provides
$approx1/3$ of the support against gravity in this region. Our comparisons to
MLT suggest a mixing length of $alpha=3-4$, consistent with the sizes of
convective plumes seen in the simulations. The temporal variability of these 3D
models is mostly on the timescale of the convective plume lifetimes
($approx300$ days), with amplitudes consistent with those observed
photometrically.
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