HII region variability and pre-main-sequence evolution

Abstract

Recent observations and simulations have suggested that HII regions around massive stars may vary in their size and emitted flux on timescales short enough to be observed. This variability can have a number of causes, ranging from environmental causes to variability of the ionizing source itself. We explore the latter possibility by considering the pre-main-sequence evolution of massive protostars and conducting numerical simulations with ionizing radiation feedback using the FLASH AMR hydrodynamics code. We investigate three different models: a simple ZAMS model, a self-consistent one-zone model by Offner et al. (2009), and a model fit to the tracks computed by Hosokawa & Omukai (2009). The protostellar models show that hypercompact HII regions around massive, isolated protostars collapse or shrink from diameters of 80 or 300 AU, depending on the model choice, down to near absence during the swelling of stellar radius that accompanies the protostar's transition from a convective to a radiative internal structure. This occurs on timescales as short as ~3000 years.

8 pages, 2 figures. Accepted to ApJ

References in corpus (5)

• The Effects of Radiative Transfer on Low-Mass Star Formation
• Limiting Accretion onto Massive Stars by Fragmentation-Induced Starvation
• Understanding Spatial and Spectral Morphologies of Ultracompact H II Regions
• Monitoring the Large Proper Motions of Radio Sources in the Orion BN/KL Region
• Time Variation in G24.78+0.08 A1: Evidence for an Accreting Hypercompact H II Region?

Cited by in corpus (13)

• Simulating the Formation of Massive Protostars: I. Radiative Feedback and Accretion Disks
• On the simultaneous evolution of massive protostars and their host cores
• Characterization of the MALT90 Survey and the Mopra Telescope at 90 GHz
• Filamentary flow and magnetic geometry in evolving cluster-forming molecular cloud clumps
• Establishing the evolutionary timescales of the massive star formation process through chemistry
• The evolution of young HII regions
• Ultra Violet Escape Fractions from Giant Molecular Clouds During Early Cluster Formation
• Impact of initial models and variable accretion rates on the pre-main-sequence evolution of massive and intermediate-mass stars and the early evolution of HII regions
• The compact, time-variable radio source projected inside W3(OH): Evidence for a Photoevaporated Disk?
• Searching for compact radio sources associated to UCHII regions
• Surveys of Clumps, Cores, and Condensations in the Cygnus X: II. Radio Properties of the Massive Dense Cores
• Dynamic Massive Star Formation: Radio Flux Variability in UCHII Regions
• Interstellar medium and star formation studies with the Square Kilometre Array