Do Internal Gravity Waves Matter for SLF Variability? 3D Hydrodynamic Simulations of 25 Msun Zero Age Main-Sequence Star
Authors: Pathak, Praneet, Blouin, Simon, Herwig, Falk, R. Woodward, Paul
Type: Presentation
Published: 2026-07-11
Keywords: Massive stars, Hydrodynamical Simulations, Internal Gravity Waves, Stellar Oscillations

<p class="font-claude-response-body break-words whitespace-normal">The origin of stochastic low-frequency (SLF) photometric variability observed in OB-type stars by CoRoT, Kepler, and TESS remains debated. SLF variability appears as a broadband, red-noise-like continuum in the light-curve power spectrum, ubiquitous across the OB domain of the main sequence but without a consensus physical origin. Core-generated internal gravity waves (IGWs) were long thought to be the driver, but <a href="https://www.nature.com/articles/s41550-023-02040-7">Anders et al. (2023)</a> showed that radiative damping in the envelope prevents such waves from reaching the photosphere.</p>
<p class="font-claude-response-body break-words whitespace-normal">I will present results from the first 3D hydrodynamic PPMstar simulations of a 25 <span class="katex"><span class="katex-mathml">M⊙</span><span class="katex-html"><span class="base"><span class="mord"><span class="msupsub"><span class="vlist-t vlist-t2"><span class="vlist-r"><span class="vlist-s"></span></span></span></span></span></span></span></span> main-sequence star that simultaneously resolve core convection, the radiative envelope, and the thin near-surface iron-opacity convection zone (<a href="https://iopscience.iop.org/article/10.3847/1538-4357/ae4487/meta">Pathak et al. 2026, ApJ, 1000, 89</a>). The simulations show that IGWs excited at the envelope convection zone — not at the core — remain surface-visible and imprint a broadband SLF continuum on the luminosity power spectrum that matches CoRoT and TESS observations of HD 46150 in both slope and amplitude. Discrete eigenmode features are also identified in the simulated spectra, providing a new asteroseismic handle on massive-star envelope physics.</p>
<p class="font-claude-response-body break-words whitespace-normal">Beyond this published work, I will present new results on the geometric effect on the observability of individual eigenmodes. By integrating surface fluctuations with appropriate spherical-harmonic response functions, we quantify how mode visibility depends on horizontal wavenumber <span class="katex"><span class="katex-mathml">ℓ</span></span>, inclination, and the radial depth of the mode cavity. We find that only a restricted set of <span class="katex"><span class="katex-mathml">(ℓ,m)</span></span> modes contribute significantly to disk-integrated photometry, and that geometric cancellation preferentially suppresses residual core-excited signal relative to the envelope-excited modes. This sharpens the connection between 3D-simulation predictions and what TESS and PLATO can actually see.</p>
<p class="font-claude-response-body break-words whitespace-normal">These results establish 3D hydrodynamic simulations as a quantitative tool for interpreting SLF variability and motivate a new generation of asteroseismic diagnostics for massive-star envelope convection, angular momentum transport, and near-surface mixing — directly relevant to the PLATO massive-star science case.</p>