Hydrodynamical models of cometary HII regions

Abstract

We have modelled the evolution of cometary HII regions produced by zero-age main-sequence stars of O and B spectral types, which are driving strong winds and are born off-centre from spherically symmetric cores with power-law ($\alpha =2$) density slopes. A model parameter grid was produced that spans stellar mass, age and core density. Exploring this parameter space we investigated limb-brightening, a feature commonly seen in cometary HII regions. We found that stars with mass $M_{\star }\ge 12{\mathrm{M}}_{\odot }$ produce this feature. Our models have a cavity bounded by a contact discontinuity separating hot shocked wind and ionised ambient gas that is similar in size to the surrounding HII region. Due to early pressure confinement we did not see shocks outside of the contact discontinuity for stars with $M_{\star }\le 40{\mathrm{M}}_{\odot }$, but the cavities were found to continue to grow. The cavity size in each model plateaus as the HII region stagnates. The spectral energy distributions of our models are similar to those from identical stars evolving in uniform density fields. The turn-over frequency is slightly lower in our power-law models due to a higher proportion of low density gas covered by the HII regions.

20 pages, 15 figures

References in corpus (4)

• A Grid of NLTE Line-Blanketed Model Atmospheres of Early B-type Stars
• The Luminosity Functions and Timescales of MYSOs and Compact HII regions
• Dynamical Expansion of H II Regions from Ultracompact to Compact Sizes in Turbulent, Self-Gravitating Molecular Clouds
• Off-center HII regions in power-law density distributions

Cited by in corpus (4)

• Modeling UV Radiation Feedback from Massive Stars: I. Implementation of Adaptive Ray Tracing Method and Tests
• A population of hypercompact HII regions identified from young HII regions
• Shape Analysis of HII Regions -- II. Synthetic Observations
• GTC/CanariCam Mid-IR Polarimetry of Magnetic Fields in Star-Forming Region W51 IRS2