Outflow-Confined HII regions. II. The Early Break-Out Phase

Abstract

In this series of papers, we model the formation and evolution of the photoionized region and its observational signatures during massive star formation. Here we focus on the early break out of the photoionized region into the outflow cavity. Using results of 3-D magnetohydrodynamic-outflow simulations and protostellar evolution calculations, we perform post-processing radiative-transfer. The photoionized region first appears at a protostellar mass of 10Msun in our fiducial model, and is confined to within 10-100AU by the dense inner outflow, similar to some observed very small hypercompact HII regions. Since the ionizing luminosity of the massive protostar increases dramatically as Kelvin-Helmholz (KH) contraction proceeds, the photoionized region breaks out to the entire outflow region in <10,000yr. Accordingly, the radio free-free emission brightens significantly in this stage. In our fiducial model, the radio luminosity at 10 GHz changes from 0.1 mJy kpc2 at m=11Msun to 100 mJy kpc2 at 16Msun, while the infrared luminosity increases by less than a factor of two. The radio spectral index also changes in the break-out phase from the optically thick value of 2 to the partially optically thin value of 0.6. Additionally, we demonstrate that short-timescale variation in free-free flux would be induced by an accretion burst. The outflow density is enhanced in the accretion burst phase, which leads to a smaller ionized region and weaker free-free emission. The radio luminosity may decrease by one order of magnitude during such bursts, while the infrared luminosity is much less affected, since internal protostellar luminosity dominates over accretion luminosity after KH contraction starts. Such variability may be observable on timescales as short 10-100 yr, if accretion bursts are driven by disk instabilities.

arXiv comment9 pages, 5 figures, accepted for publication in ApJ

References in corpus (34)

• The Formation of Massive Stars from Turbulent Cores
• The distance to the Orion Nebula
• The Formation of Massive Star Systems by Accretion
• Evolution of Massive Protostars via Disk Accretion
• Disk-mediated accretion burst in a high-mass young stellar object
• Three-dimensional simulation of massive star formation in the disk accretion scenario
• Variable protostellar accretion with episodic bursts
• An extraordinary outburst in the massive protostellar system NGC6334I-MM1: quadrupling of the millimeter continuum
• The RMS Survey: Critical Tests of Accretion Models for the Formation of Massive Stars
• Gravitational Collapse and Star Formation in Logotropic and Non-Isothermal Spheres
• On the existence of accretion-driven bursts in massive star formation
• G11.92-0.61 MM1: A Keplerian disc around a massive young proto-O star
• Grand Design Spiral Arms in A Young Forming Circumstellar Disk
• Early stages of cluster formation: fragmentation of massive dense cores down to ~1000 AU
• Outflow-Confined H II Regions. I. First Signposts of Massive Star Formation
• Imaging the Ionized Disk of the High-Mass Protostar Orion-I
• Weak and Compact Radio Emission in Early High-Mass Star Forming Regions: I. VLA Observations
• The Impact of Feedback During Massive Star Formation by Core Accretion
• Massive Outflows Driven by Magnetic Effects in Star Forming Clouds with High Mass Accretion Rates
• The Collimated Jet Source in IRAS 16547-4247: Time Variation, Possible Precession, and Upper Limits to the Proper Motions Along the Jet Axis
• Radiation Transfer of Models of Massive Star Formation. III. The Evolutionary Sequence
• Search for ionized jets towards high-mass young stellar objects
• Radiation Transfer of Models of Massive Star Formation. I. Dependence on Basic Core Properties
• Observing the onset of outflow collimation in a massive protostar
• Variable Accretion Rates and Fluffy First Stars
• Low-Metallicity Protostars and the Maximum Stellar Mass Resulting from Radiative Feedback
• Photoevaporation of Circumstellar Disks Revisited: The Dust-Free Case
• The Population of Compact Radio Sources in the Orion Nebula Cluster
• ALMA Observations of Orion Source I at 350 and 660 GHz
• Large-Scale Kinematics, Astrochemistry and Magnetic Field Studies of Massive Star-forming Regions through HC3N, HNC and C2H Mappings
• Radiation Transfer of Models of Massive Star Formation. II. Effects of the Outflow
• A Massive Protostar Forming by Ordered Collapse of a Dense, Massive Core
• HST-Scale 3D simulations of MHD disc winds : A rotating two-component jet structure
• ALMA Imaging of Millimeter/Submillimeter Continuum Emission in Orion KL

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• The SOMA Radio Survey. I. Comprehensive SEDs Of High-Mass Protostars From Infrared To Radio And The Emergence Of Ionization Feedback
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• The SOFIA Massive (SOMA) Star Formation Q-band Follow-up. II. Hydrogen Recombination Lines Toward High-Mass Protostars