On the formation and expansion of H II regions

Franco, J.; Tenorio-Tagle, G.; Bodenheimer, Peter

doi:10.1086/168300

Cited by 172 publications

(228 citation statements)

References 0 publications

Supporting

Mentioning

211

Contrasting

Order By: Relevance

“…However, not all H ii regions are gravitationally trapped, and this model will not be appropriate for many observed H ii regions. In particular, H ii regions with cometary or arc-shaped morphologies are likely to be rapid outflows, '' champagne '' flows, down steep density gradients in the surrounding molecular gas (Tenorio-Tagle 1979;Franco, Tenorio-Tagle & Bodenheimer 1990;Keto et al 1995;Shu et al 2002). H ii regions with irregular or shell-like morphologies are not well explained but are unlikely candidates for trapping.…”

Section: The Lifetimes Of Uc H II Regionmentioning

confidence: 99%

The Formation of Massive Stars by Accretion through Trapped Hypercompact HiiRegions

Keto¹

2003

ApJ

197

189

View full text Add to dashboard Cite

The formation of massive stars may take place at relatively low accretion rates over a long period of time if the accretion can continue past the onset of core hydrogen ignition. The accretion may continue despite the formation of an ionized H ii region around the star if the H ii region is small enough that the gravitational attraction of the star dominates the thermal pressure of the H ii region. The accretion may continue despite radiation pressure acting against dust grains in the molecular gas if the momentum of the accretion flow is sufficient to push the dust grains through a narrow zone of high dust opacity at the ionization boundary and into the H ii region where the dust is sublimated. This model of massive star formation by continuing accretion predicts a new class of gravitationally trapped, long-lived, hypercompact H ii regions. The observational characteristics of the trapped hypercompact H ii regions can be predicted for comparison with observations.

show abstract

Section: The Lifetimes Of Uc H II Regionmentioning

confidence: 99%

The Formation of Massive Stars by Accretion through Trapped Hypercompact HiiRegions

Keto¹

2003

ApJ

197

189

View full text Add to dashboard Cite

show abstract

“…The H ii regions are egg-shaped (elongated in the directions of lower density); they may even be open in these directions if the ionizing photon flux is high or if the ambient density is low. The formation and expansion of H ii regions in clouds with a power-law density stratification, r −w , and in isothermal self-gravitating disks was described by Franco et al (1990). For power-law profiles, there is a critical value of w above which the cloud is entirely ionized.…”

Section: Morphology and Evolution Of An H II Regionmentioning

confidence: 99%

A gallery of bubbles

Deharveng

Schüller

Anderson

et al. 2010

A&A

364

584

View full text Add to dashboard Cite

Context. This study deals with infrared bubbles, the H ii regions they enclose, and triggered massive-star formation on their borders.Aims. We attempt to determine the nature of the bubbles observed by Spitzer in the Galactic plane, mainly to establish if possible their association with massive stars. We take advantage of the very simple morphology of these objects to search for star formation triggered by H ii regions, and to estimate the importance of this mode of star formation.Methods. We consider a sample of 102 bubbles detected by Spitzer-GLIMPSE, and catalogued by Churchwell et al. (2006; hereafter CH06). We use mid-infrared and radio-continuum public data (respectively the Spitzer-GLIMPSE and -MIPSGAL surveys and the MAGPIS and VGPS surveys) to discuss their nature. We use the ATLASGAL survey at 870 μm to search for dense neutral material collected on their borders. The 870 μm data traces the distribution of cold dust, thus of the dense neutral material where stars may form. Results. We find that 86% of the bubbles contain ionized gas detected by means of its radio-continuum emission at 20-cm. Thus, most of the bubbles observed at 8.0 μm enclose H ii regions ionized by O-B2 stars. This finding differs from the earlier CH06 results (∼25% of the bubbles enclosing H ii regions). Ninety-eight percent of the bubbles exhibit 24 μm emission in their central regions. The ionized regions at the center of the 8.0 μm bubbles seem to be devoid of PAHs but contain hot dust. PAH emission at 8.0 μm is observed in the direction of the photodissociation regions surrounding the ionized gas. Among the 65 regions for which the angular resolution of the observations is high enough to resolve the spatial distribution of cold dust at 870 μm, we find that 40% are surrounded by cold dust, and that another 28% contain interacting condensations. The former are good candidates for the collect and collapse process, as they display an accumulation of dense material at their borders. The latter are good candidates for the compression of pre-existing condensations by the ionized gas. Thirteen bubbles exhibit associated ultracompact H ii regions in the direction of dust condensations adjacent to their ionization fronts. Another five show methanol masers in similar condensations. Conclusions. Our results suggest that more than a quarter of the bubbles may have triggered the formation of massive objects.Therefore, star formation triggered by H ii regions may be an important process, especially for massive-star formation.

show abstract

“…Equation (13) shows that ionization equilibrium is only possible if the density profile n e $ r À has a slope less steep than ¼ 3=2 (Franco et al 1990). Since the densities of the accretion solution (Fig.…”

Section: Description Of the Modelmentioning

confidence: 99%

“…Descriptions can be found in standard textbooks such as Spitzer (1978), Dyson & Williams (1980), and Shu (1992). This classic model for pressure-driven expansion has also been extended by Franco, Tenorio-Tagle, & Bodenheimer (1990) to describe the evolution of H ii regions within clouds that have power-law density gradients.…”

Section: Introductionmentioning

confidence: 99%

On the Evolution of Ultracompact HiiRegions

Keto

2002

ApJ

122

124

View full text Add to dashboard Cite

The classic model for the pressure-driven expansion of H ii regions is reevaluated to include the gravitational force of the star responsible for the H ii region. The model shows that the gravitational attraction of the star maintains a steep density gradient and accretion flow within the ionized gas and prevents the H ii region from expanding hydrodynamically unless the radius of ionization equilibrium is beyond the radius where the sound speed of the ionized gas approximates the escape velocity. Once past this critical radius, the H ii region will expand rapidly and the accretion flow through the H ii region is quickly reduced. However, in contrast to the model without gravity in which the velocity of the ionized gas is everywhere outward, in the model with gravity, the velocity within the H ii region is always inward. Newly formed massive stars within dense molecular cores may initially form very small H ii regions that at first evolve slowly through an increase in ionizing flux, as would be caused by an increase in the mass or number of stars through continuing accretion through the H ii region.

show abstract

On the formation and expansion of H II regions

Cited by 172 publications

References 0 publications

The Formation of Massive Stars by Accretion through Trapped Hypercompact HiiRegions

The Formation of Massive Stars by Accretion through Trapped Hypercompact HiiRegions

A gallery of bubbles

On the Evolution of Ultracompact HiiRegions

Contact Info

Product

Resources

About