Determine the iron content of red-supergiant silicate dust

Determine whether silicate grains formed in red-supergiant circumstellar environments are sufficiently iron-poor for laboratory-measured, forsterite-like optical constants to provide an appropriate description of their dust opacity.

Background

The paper finds that the assumed silicate optical constants strongly affect the inferred dust densities and mass-loss rates from spectral-energy-distribution modeling. Iron-poor laboratory silicates require substantially more dust than empirical astronomical silicates to reproduce the observed infrared emission, thereby changing the inferred gas-to-dust ratios.

The physical applicability of the iron-poor laboratory opacity model depends on whether silicate grains formed in red-supergiant winds incorporate little iron. The paper identifies this as unresolved because iron incorporation depends on the grain-condensation sequence and local wind conditions.

References

Whether RSG silicates are formed sufficiently Fe-poor for laboratory forsterite-like optical constants to be appropriate is still uncertain, as Fe incorporation is expected to depend on the grain condensation sequence and local wind conditions \citep{Speck2000_Orich_dustcomp,Verhoelst2009_RSG_dustcond}.

— The Molecular Circumstellar Environments of Red Supergiants in Galactic Open Clusters  (2609.31362 - Siebert et al., 25 Sep 2026) in Section 4.2.2, subsection “Comparing CO and SED models”