Kinematics and Structure of Ionized Gas in the UCHII Regions of W33 Main

TL;DR

This study combines high-resolution observations and simulations to analyze the complex gas structures and stellar dynamics within the UCHII regions of W33 Main, revealing multiple exciting stars and their trajectories.

Contribution

It introduces a novel approach of integrating detailed observational data with 3D hydrodynamic and radiative transfer simulations to interpret UCHII region morphologies.

Findings

Multiple exciting stars likely exist in each sub-source.

Stellar trajectories influence the dynamical evolution of the proto-cluster.

Models successfully reproduce observed gas structures and kinematics.

Abstract

High mass proto-stars create Ultra-Compact Hii regions (UCHII) at the stage of evolution when most of the accretion is finished but the star is still heavily embedded in molecular material. The morphologies of UCHII regions reflect the interactions of stellar winds, stellar motions, and density structure in the molecular cloud; they are complex and it has been very difficult to interpret them. We here present data obtained with TEXES on the NASA IRTF of the [NeII] emission line in the proto-cluster of young OB stars in W33 Main. The data cube has a spatial resolution of ~ 1.4 arcsec and true velocity resolution ~ 5 km/s; with A ~ 0.02Av it is relatively unaffected by extinction. We have run 3D hydrodynamic and line profile simulations, using PLUTO and RADMC-3D, of the gas structures created by multiple windy stars moving relative to each other through the ambient cloud. By iterative comparison of the data cube and the simulations, we arrive at models that reproduce the different morphology and kinematic structure of each UCHII region in W33 Main. The results indicate that each sub-source probably holds multiple exciting stars, permitting an improved view of the stellar population, and finds the stellar trajectories, which may determine the dynamical development of the proto-cluster.