Related papers: Clumpy Ultracompact HII Regions I: Fully Supersoni…
Cometary ultracompact HII regions have been modelled as the interaction of the hypersonic wind from a moving star with the molecular cloud which surrounds the star. We here show that a similar morphology can ensue even if the star is…
Many ultracompact HII regions exhibit a cometary morphology in radio continuum emission. In such regions, a young massive star is probably ablating, through its ultraviolet radiation, the molecular cloud clump that spawned it. On one side…
We have modelled ultracompact HII regions (UCHIIR) in terms of steady subsonic ionized flows in a clumpy medium. Mass loss from neutral clumps allows the regions to be long-lived. We examine the form of global flows for different…
The presence of giant shells or loops in giant HII regions are clear witness of the mechanical energy input from massive stars. Here we evaluate the impact that winds may have on the structure of giant nebulae and on their supersonic…
Massive stars influence the surrounding universe far out of proportion to their numbers through ionizing radiation, supernova explosions, and heavy element production. Their formation requires the collapse of massive interstellar gas clouds…
The dynamical evolution of HII regions with and without stellar motion in dense, structured molecular clouds is studied. Clouds are modeled in hydrostatic equilibrium, with gaussian central cores and external halos that obey r**-2 and r**-3…
Ultracompact and hypercompact HII regions appear when a star with a mass larger than about 15 solar masses starts to ionize its own environment. Recent observations of time variability in these objects are one of the pieces of evidence that…
We examine the effects of ionization, radiation pressure and main sequence winds from massive stars on self-gravitating, clumpy molecular clouds, thereby modeling the formation and pre-supernova feedback of massive star clusters. We find…
We review some recent observational results on the properties of ultracompact HII regions, in particular the presence of extended continuum emission surrounding ultracompact sources and the discovery of a new class of so-called…
Here we discuss the interaction of massive stars with their parental molecular clouds. A summary of the dynamical evolution of HII regions and wind-driven bubbles in high-pressure cloud cores is given. Both ultracompact HII regions and…
The accepted explanation of the observed dichotomy of two orders of magnitude between in situ measurements of electron density in HII regions, derived from emission line ratios, and average measurements based on integrated emission measure,…
Hypercompact HII regions (HC) are regions of ionized gas associated with the early stages of high-mass star formation. With the aim of better understanding their characteristics, we studied five candidate HC HII regions. Here, we present…
Ultracompact HII regions are signposts of massive star formation and their properties provide diagnostics for the characteristics of very young O stars embedded in molecular clouds. While radio observations have given us a good picture of…
Massive stars are expected to produce wind-blown bubbles in the interstellar medium; however, ring nebulae, suggesting the existence of bubbles, are rarely seen around main-sequence O stars. To search for wind-blown bubbles around…
We review the structural properties of giant extragalactic HII regions and HII galaxies based on two dimensional hydrodynamic calculations, and propose an evolutionary sequence that accounts for their observed detailed structure. The model…
We carried out 13CO J=1-0, CS, and C34S J=2-1 and J=3-2 line observations of molecular clouds associated with 16 ultracompact (UC) HII regions with extended envelopes. The molecular clouds are the ones that give birth to rich stellar…
The observed parameters of the young superstar cluster M82-A1 and its associated compact HII region are here shown to indicate a low heating efficiency or immediate loss, through radiative cooling, of a large fraction of the energy inserted…
HII galaxies are clumpy and their gas kinematics can be mapped to show the global turbulent motions and the effect of massive star evolution. The distribution of their physical conditions is homogeneous and oxygen abundance is uniform. The…
We present the first results of a project aimed at the combined study of massive stars and their surrounding nebulae by means of a detailed study of Galactic HII regions ionized by only one massive star. With this, we intend to check the…
Velocity shifts and differential broadening of radio recombination lines are used to estimate the densities and velocities of the ionized gas in several hypercompact and ultracompact HII regions. These small HII regions are thought to be at…