Constrain the initial and turbulent velocities in cluster red-supergiant winds

Constrain the initial outflow velocity $v_0$ and the turbulent velocity in the circumstellar envelopes of the modeled RSGC1 and RSGC2 red supergiants so that the adopted CO radiative-transfer velocity structure is empirically determined rather than assumed.

Background

The CO radiative-transfer models adopt a velocity law with an initial velocity of v0=3v_0=3 km s−1^{-1}, an expansion velocity measured from molecular-line profiles, and a spatially constant turbulent velocity of 1 km s−1^{-1}. These latter two components affect the modeled line profiles and therefore the inferred mass-loss parameters.

The authors explicitly state that the initial and turbulent velocities have not been measured for the RSGs in their sample. The open observational issue is to obtain constraints on these quantities rather than relying on commonly adopted values from models of other evolved-star circumstellar envelopes.

References

Neither $v_0$, nor the turbulent velocity are currently constrained for the modeled RSGs, but this velocity profile is commonly assumed for the CSEs of evolved stars where the gas is assumed to be accelerated by momentum exchange between dust grains and gas \citep[e.g.][]{decin2010}.

— The Molecular Circumstellar Environments of Red Supergiants in Galactic Open Clusters  (2609.31362 - Siebert et al., 25 Sep 2026) in Section 3.5.1, subsection “Radiative-transfer modeling approach”