Found 15 talks width keyword HII regions
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.
AbstractEl 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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- The nature of gamma-ray binariesDr. Alicia LopezTuesday June 27, 2017 - 12:30
- The Basis for Cosmic Ray Feedback: Written on the WindProf. Ellen ZweibelThursday June 29, 2017 - 10:30