Kavli Affiliate: Lars Bildsten
| First 5 Authors: William C. Schultz, Benny T. H. Tsang, Lars Bildsten, Yan-Fei Jiang,
| Summary:
Observations indicate that turbulent motions are present on most massive star
surfaces. Starting from the observed phenomena of spectral lines with widths
much larger than thermal broadening (e.g. micro- and macroturbulence) to the
detection of stochastic low-frequency variability (SLFV) in the Transiting
Exoplanet Survey Satellite photometry, these stars clearly have large scale
turbulent motions on their surfaces. The cause of this turbulence is debated,
with near-surface convection zones, core internal gravity waves, and wind
variability being proposed. Our 3D grey radiation hydrodynamic (RHD) models
characterized the surfaces’ convective dynamics driven by near-surface
convection zones and provided a reasonable match to the observed SLFV in the
most luminous massive stars. We now explore the complex emitting surfaces of
these 3D RHD models, which strongly violate the 1D assumption of a plane
parallel atmosphere. By post-processing the grey RHD models with the Monte
Carlo radiation transport code SEDONA, we synthesize stellar spectra and
extract information from the broadening of individual photospheric lines. The
use of SEDONA enables the calculation of the viewing angle and temporal
dependence of spectral absorption line profiles. Combining uncorrelated
temporal snapshots together, we compare the broadening from the 3D RHD models’
velocity fields to the thermal broadening of the extended emitting region,
showing that our synthesized spectral lines closely resemble the observed
macroturbulent broadening from similarly luminous stars. More generally, the
new techniques we have developed will allow for systematic studies of the
origin of turbulent velocity broadening from any future 3D simulations.
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