NEBULAE

Author: GARCIA ROJAS JORGE.
Year: 2006.
University: LA LAGUNA [www.ull.es].
Place of defense: FACULTAD DE FISICA. UNIVERSIDAD DE LA LAGUNA.
Place of preparation: INSTITUTO DE ASTROFISICA DE CANARIAS.

Summary: The H II regions are objects central to the understanding of the chemical composition and evolution in the universe, especially in the realm extragaláctico. Because of this it is essential to know if traditional methods for determining abundances in nebulae ionised (based on the analysis of lines excitation colisional) are reliable or not. The main objective of this dissertation is to determine the abundance of alternative form of certain ions (O + +, C + +, O + and Ne + + from the intensity of recombination lines, much weaker than the lines excitation colisional but spectra measured in deep enough . previous results obtained for the H II regions galactic and extragalactic brightest showed that the abundances calculated from recombination lines are consistently higher (up to a factor 2-3) that certain lines from excitation colisional. This problem ( known as "discrepancy abundances") may be related to the presence of temperature fluctuations in the nebulae. This thesis presents a detailed analysis of data espectrofotométricos areas brilliant 8 regions galactic H II. data were acquired with the spectrograph echelle UVES (Ultraviolet Visual Echelle Spectrograph) telescope Kueyen of VLT (Very Large Telescope), the Center of Cerro Paranal, Chile, during two campaigns observation. every object has covered a wide range of length wave (3100-10400 Ã), with a spectral resolution effectively R = 8800. We found several hundred emission lines in each region (in total have been measured over 2600 lines), forming the most detailed observations this kind undertaken so far in H II regions. Thanks to the enormous amount of information available has been able to determine the physical conditions of gas (electron density and temperature) from large numbers of diagnoses involving relations between lines or broadcast between the continuous emission lines. From these physical conditions, we determined the abundances of large numbers of ions using lines excitation colisional. depth of the spectra available has also allowed us to determine the abundances of O + +, C + +, and some cases Ne + and O + + from recombination lines. was obtained parameter t2 (quadratic fluctuation average temperature) using various methods: a) by comparing the electronic temperatures obtained from the Balmer jumps and / or Paschen of HIya from ratios lines excitation colisional b) comparing the ionic abundances of O + + (and in some cases C + +, O + and Ne + +) obtained from recombination lines and lines of excitement colisional; c) from the spectrum of recombination I have to I. The results obtained using different methods are generally consistent with one another. The parameter t2 means for each object has been used to estimate the abundances of many ions in the presence of temperature fluctuations. The extent of recombination lines of O + + and C + + in all objects has allowed the identification gradient OyC in the galactic disk. Harvesting these gradients is precisely one of the most important constraints for models of formation and chemical evolution of the disk of the Galaxy and the solar neighborhood. This is the first time that determines the gradient of C for a significant number of H II regions distributed in such a wide range of distances galactocéntricas. The value of the abundances of OyC in the vicinity solar coincides with the most recent values of the abundances of OyC in the Sun, taking into account the evolving chemistry experienced in this area of the Galaxy since the formation of our star. Finally, we conducted the overall analysis of the sample in which we compared the different diagnoses of temperature and density, and where we have made a comparative study between two of the proposed scenarios to explain the discrepancy in abundances of planetary nebulae and H II regions: existence 8 of fluct 3ee uaciones temperature and the presence of inhomogeneidades chemical colder and denser the surrounding interstellar medium. In this thesis we have found that there is a significant difference between the results obtained in NP and H II regions remain, in the latter, consistent with the scenario of temperature fluctuations.