Found 57 talks archived in The Galaxy
Abstract
The 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.
Abstract
The study of the Milky is expected to have a major impact on our understanding of how galaxies form and evolve. "Near-field cosmology" is being vigorously pursued through a series of major surveys of the Galaxy's stellar content (2-MASS, SDSS, RAVE, Hermes, Apogee, Gaia) that are either in hand or pending. It will be argued that what we want to know is deeply buried in these data and can only be extracted by comparing the surveys with a hierarchy of dynamical models of ever increasing complexity. Work currently being done to build such hierarchical models will be described, and some early results from this work will be summarised.
Abstract
The Orion star forming region is an ideal laboratory for many astrophysical studies. In this talk I will present a study of the chemical composition of early B-type stars in the Orion OB1 association. The main ideas I will talk about are: (1) The importance of self-consistent spectroscopic techniques for the abundance analysis in this type of stellar objects; (2) the study of the homogeneity of abundances in stars from the various stellar subgroups in OriOB1; (3) the comparison of O stellar abundances with recent Solar determinations; (4) the comparison of stellar abundances with those resulting from the analysis of the emission line spectra of the Orion nebula (M42); (5) the study of the oxygen depletion onto dust grains in the Orion nebula. La región de formación estelar de Orión es una laboratorio perfecto para muchos tipos de estudios en astrofísica. En esta charla me centraré en el estudio de abundancias de las estrellas de tipo B temprano presentes en la asociación OriOB1. Las principales ideas que presentaré son: (1) La importancia de los análisis espectroscópicos detallados en la determinación de abundancias en estrellas de tipo B temprano; (2) el estudio de la homogeneidad química de los distintos subgrupos estelares que componen OriOB1; (3) la comparación de la abundancias estelares de oxígeno con determinaciones recientes en el Sol; (4) La comparación de abundancias estelares con aquellas obtenidas a partir de análisis del espectro de M42, la nebulosa de Orion; (5) el estudio de la depleción de oxígeno en granos de polvo en la nebulosa de Orión.
Abstract
The last few years have witnessed a growing amount of empirical evidence pointing to the existence of multiple stellar populations in some Galactic globular clusters. It is also becoming more and more clear that clusters, hosting multiple stellar populations, do share some common properties, but also differ from each other in various aspects. In this talk, I will review the recent results concerning the presence of multiple stellar populations in stellar clusters, emphasizing the (different) properties of the subpopulations in the various clusters, and how they have been interpreted so far. I will discuss also the global characteristics of "peculiar" clusters - hosting multiple populations - from different points of view, and compare them with "normal" clusters, to try and shed some light on their nature and origin.
Abstract
Based on observations with the Advanced Camera for Surveys (ACS), I will present accurate relative ages for a sample of 64 Galactic globular clusters. This Hubble Space Telescope (HST) Treasury program has been designed to provide a new large, deep and homogeneous photometric database. Relative ages have been obtained using a main sequence fitting procedure between clusters in the sample. Relative ages are determined with an accuracy from 2% to 7%. It has been proved that derived ages are independent of the assumed theoretical models. The existence of two well defined Galactic globular cluster groups is found. A group of old globular clusters with an age dispersion of 6% and showing no age-metallicity relation, and, on the other hand, a younger group showing a clear age-metallicity relation similar to that found in the globular clusters associated to the Sagittarius dwarf galaxy. Roughly 1/3 of the clusters belong to the younger group. Considering these new results, it is very tempting to suggest a Milky Way's halo formation scenario in which two differentiated phases took place. A very fast collapse, where the old and coeval globular clusters where formed, followed by accretions of Milky Way's satellite galaxies.
Abstract
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.
Abstract
I present the first results of a long term project devoted to the study of the evolution of the binary population in globular clusters. Using deep ACS@HST images of a sample of 13 globular clusters I estimated the fraction of binaries in the cores of these clusters. From a theoretical side, I developed a simplified analytical code which simulates the evolution of the properties of the binary population in a dynamically evolving globular cluster. The comparison between theory and observations allows to evaluate the efficiency of the various processes of binary formation and destruction in these stellar systems and their dependence on the main cluster structural and dynamical parameters.
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