Found 16 talks width keyword HII regions
AbstractThe properties of molecular clouds associated with 10 H II regions were studied using CO observations. We identified 142 dense clumps within our sample and measured and calculated physical properties of the clumps such as size, excitation temperature, line widths, density and mass. We found that our sources are divided into two categories: those that show a size-line width relation ("type I") and those which do not show any relation ("type II"). Type II sources have larger line widths in general. Investigating the relation between the line width and other parameters shows that while the MLTE (Local Thermodynamic Equilibrium mass) increases with ΔV (line width) for both 12CO(2-1) and 13CO(2-1) lines in type I sources, no relation was found for type II sources. No relation between column density and line width was found for either category. We also investigated how the characteristics of the clumps vary with distance from the HII region. We found no relation between mass distribution of the clumps and distance from the ionization front, but a weak decrease of the excitation temperature with increasing distance from the ionized gas. Only the projected distance is measured in our study which is equal or smaller than the true value. Therefore we compared the results by a Monte Carlo simulation of a central heating source and found that for small distances the relation is very scattered, which is consistent with our results. No relation was found between line width and distance from the H II region which probably indicates that the internal dynamics of the clumps is not affected by the ionized gas. Internal sources of turbulence, such as outflows and stellar winds from young proto-stars may have a more important role.
AbstractWhen we measure the electron density within an H II region using ratios of emission lines we find characteristic values in the range of 100-300 cm-3. But when we make these measurements using the total luminosity in Hα and the overall radial size of an H II region we find average values in the range 3-10. I will first explain how this discrepancy occurs, and then go on to show some measurements of electron densities in the H II regions of M51 (over 2500 regions) and the dwarf galaxy NGC 4449 (over 250 regions) using the second method, by Leonel Gutiérrez and myself. From these measurements we can infer how the electron density varies with the radial size of an individual region, and how it varies as we move from the center of the galaxy disc to the outside. Some interesting simple global relationships are found, which tell us about the interaction of star forming regions with their surroundings and how this interaction varies across the face of a galaxy.
The formation of massive stars is not fully understood. The high luminosity and temperature of massive protostars complicate the accretion mechanism at work in intermediate and low mass young stellar objects. Nonetheless, several scenarios exist to explain the formation of massive stars. In this talk, we will focus on the process of triggered star formation on the borders of H II regions. Due to the feedback effects of OB stars, a layer of molecular material is collected during the expansion of the H II region. Instabilities develop in this layer and give birth to new stars. We will present a detailed study of three Galactic H II regions (RCW79, RCW82 and RCW120). Near-infrared integral field observations have been carried out with SINFONI on the VLT. We will see how they reveal the nature of both the ionizing stars and of the YSOs in the collected layer and how they support the scenario of 'triggered star formation'.
AbstractPrimordial helium might seem to be just a tiny piece in our understanding of how the Universe was born; still, it is a piece that must fit in if we are to ensure that the whole Big Bang scenario is consistent. During the last decade, a significant effort has been aimed at achieving the necessary accuracy to achieve this goal. While we still do not have a firm handle on it, we have learned quite a few things on the way. The talk will provide a review of this quest, highlighting the uncertainties that still remain and the feedback that it has provided to our knowledge of how H II regions work.
El jovencísimo cúmulo GM 24, a una distancia de 2 kpc, se encuentra embebido en una caliente nube de CO aislada, en donde se formó hace menos de 105 años. El núcleo del cúmulo se compone de estrellas O tardías y de tipo B principalmente y pareciera carecer actualmente de una población estelar de baja masa. Se presentan nuevas observaciones en el infrarrojo cercano y medio que dan mayor definición a las características de sus principales objetos estelares jóvenes.
Common wisdom identifies hydrogen lines in photoionized region with recombination lines. However, these lines can also be excited by different atomic mechanisms, the most important of which are collisional excitation and continuum pumping by stellar photons. The relative contributions of these two mechanisms to the total Balmer intensity can be substantial in certain environments, and the associated bias can easily dominate the error budget. In this talk I will give estimates for the effectiveness of these mechanisms, defining at the same time the observational strategies that permit to minimize their contribution.
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- Problems with the dark matter and dark energy hypotheses, and alternative ideasDr. Martin Lopez CorredoiraThursday October 25, 2018 - 10:30 (Aula)