Dust from Evolved Stars—Bridging Hydrodynamics, Chemistry, and
Observations
Cool Stars 23 Splinter Session, Thursday, June 18, 2026
Goal of this splinter.
We will bring together modelers and observers across three strands to
identify a focused set of problems and shared inputs/outputs between hydrodynamical and chemical models to accelerate apples-to-apples comparisons, and
articulate the most informative current and near-term observables (flux ratios, visibilities, closure phases, polarization, resolved continuum/line morphology) and their connection to the model outputs.
Scientific rationale
The past few years have seen a step-change in our ability to model and observe dust formation and processing in the winds of evolved stars, particularly AGB stars and red supergiants. Three strands are converging:
First, hydrodynamical models now resolve multi-dimensional flows, shocks, and pulsation-driven levitation with radiative transfer in or near the loop, capturing clumpiness, drift, and feedback between gas and grains.
Second, chemical models have matured from equilibrium approximations to large, time-dependent reaction networks that track nucleation, growth, fragmentation, and gas–grain exchange under non-LTE conditions.
Third, observations from ALMA, JWST, VLTI, and advanced polarimetry now probe dust condensation radii, grain species, sizes, and morphologies at unprecedented sensitivity and angular resolution—revealing complexity (arcs, spirals, detached shells, bow shocks) that challenges 1D assumptions and tightly constrains theory.
Importantly, the same nucleation, growth, and transport physics governs condensate clouds in brown-dwarf and exoplanet atmospheres; phase-resolved JWST spectra and high-dispersion spectroscopy there provide complementary constraints on mineral species, vertical mixing, and grain size distributions that we can cross-calibrate with evolved-star winds. Yet these advances remain partially siloed.
Hydrodynamics often parameterizes chemistry; chemistry often assumes simplified flows; observations sometimes lack forward models that carry microphysics to observables. Linkages to the brown-dwarf/exoplanet cloud community are similarly thin, despite shared condensate species and opacities, and a common need to propagate microphysics to spectra, phase curves, and polarization.
The current obstacles lie in the communication between these areas: self-consistent treatments and implementations of dynamics, radiative transfer, and microphysics that predict testable diagnostics (e.g., multi-line CO and SiO, mid-IR spectral features, continuum morphology, polarization) and close the loop with data.