POSITIONAL ASTRONOMY

Author: SUÁREZ FERNÁNDEZ OLGA.
Year: 2003.
University: VIGO [www.uvigo.es].
Place of defense: FACULTAD DE CIENCIAS.
Place of preparation: FACULTADE DE CIENCIAS (CAMPUS DE VIGO).

Summary: This thesis presents a study of the stars in the post-stage evolutionary branch Asintótica of Giants, we will call post-AGB, according to its initials in English (post-Asymptotic Asymptotic Giant Branch). With this objective has conducted a search of observational stars in this evolutionary phase, which has resulted in a catalog of esepctroscopía optic bringing together 255 objects, of which 203 are stars post-AGB or planetary nebulae ( PN, the acronym in English Planetary Nebula). This catalog is the product of 15 years of observations made by our group, following selection criteria on the limit values of flux densities in bands observational satellite IRAS. The objects have been classified spectral types, whenever possible. In the case of nebuolosas planetary objects and transition have been calculated their classes excitation. As a result of these observations we obtained the most extensive and complete up to the moment of objects at the stage evolutionary post-AGB with spectral classifications. This has enabled us to perform statistical studies about the physical properties of the stars in these late stages of evolution. In particular, it has obtained the spectral energy distribution (SED, according to its initials in Spanish) of all the stars in the sample belonging to the stages of our interest, in order to jointly explore the properties and evolution of the wrapper circumestelar and the central star. These SEDs have been classified into five groups, according to the criteria defined by van der Veen et al. 1989. The five groups were characterized by the study of galactic latitude, the spectral type, chemistry and the dominant position in the diagram color-color IRAS of objects belonging to each of them. To complete the characterization and determine the status of evolution of stars according to their type of SED, a comparison was made between the distribution of spectral types found for each class of SED and distribution predicted by van Hoof et al. (1987). This comparison endorsed the results obtained using the distribution galactic latitude, and the position of the stars in the diagram colo-color, we have outlined. Based on the results obtained can establish a connection between evolutionary SED classes I and II. Both classes are completely dominated by the issue in the infrared, and optical presented strongly red. The Class II appears to be a state evolving ligeramnete more advanced Class I. In these two classes are objects that even after leaving the AGB phase, are asignificativa mass loss post-AGB. Class III is distributed in the diagram color-color IRAS feature without taking up any position. Their spectral distribution continuous dominated by the infrared emission, but the central star and begins to be clearly visible. Studying galactic latitude distribution and spectral types of stars of this kind we deduce that this is a class consisting of massive objects, but are not experiencing significant mass loss at the stage post-AGB. The spectral distribution of the classes IVa and IVb samples clearly maximum two, one in the optical corresponding to the central star, and the other in the infrared, corresponding to the wrapper. The class IVa, contains low-mass stars, whose slow evolution justify various positions in the diagram color-color without favoring a particular distribution, as with the class IVb. Without em 8 Bargo, and 7e7 No class IVb there is a larger number of objects and greater dispersion Galactic, which suggests that this is a class ", which eventually masses various objects at the end of its evolution . In this class you can find masses of relatively high already evolved enough to display two peaks in its spectral distribution, and low mass objects whose wrapper has never come to obscure the central star. This study demonstrates once the advisability of having information on several wavelengths in order to characterize the evolution of stars in the stage post-AGB. The position of one of these objects in the diagram color-color IRAS not determined unambiguously its evolutionary stage. The need to know information about your spectral distribution of energy, and combine this informaicón with spectroscopic data in the optical power to determine its nature post-AGB, its evolutionary stage and an estimate of the initial mass of the parent star. This thesis has also conducted a study on the classification of spectra using artificial intelligence techniques in collaboration with members of the Department of Technology of the Informaicón and Communications at the University of La Coruña. Specifically, it has developed an expert system that enables automatic classification of stellar spectra catalogs with a high degree of reliability. They have also been tested several groups of neural networks that have proved their efficiency in clasifiación spectral library of standard spectra.

Author: LÓPEZ SANTIAGO JAVIER.
Year: 2004.
University: COMPLUTENSE DE MADRID [www.ucm.es].
Place of defense: FACULTAD DE CIENCIAS FÍSICAS.
Place of preparation: FACULTAD DE CIENCIAS FÍSICAS.

Summary: This thesis has been to the collection, monitoring and spectral characterization of a broad sample of active young stars of the past and with spectral types belonging to different age groups kinematic younger, in order to conduct a study of the relationship between flow cromosférico emitted by the stars in the various spectral lines in the optical range and the connection between magnetic activity, rotation and age in such objects. First has compiled a list of 535 stars prospective panel members kinematic youngest of whom is studying its kinematics, photometry and abundance of lithium from the latest results found in the literature. Of these, it has selected a sample of 105 stars with measurements of radial velocity vague or does not possess your abundance of lithium in the literature, adding 39 other objects with a high level of magnetic activity or an abundance of lithium, but no measure of its radial velocity. In total, have been taken 348 spectra of high resolution of 144 stars of the show, which has conducted a detailed spectroscopic study that includes determining the radial velocity, rotation speed, abundance of lithium, level of magnetic activity in different lines cromosféricas and spectral type. With these results have conducted two parallel studies: the first related to the verification of the existence of age subgroups within groups kinematic youth and the second devoted to detailed study of the relationship flujo-flujo and actividad-rotación-edad . As for the former, it has been shown that various age subgroups within each of the groups studied kinematic: Association Local supercúmulo Hyades, a group of movement Ursa Major, supercúmulo IC 2391 and group movement Castor, in particular, it has been discovered a new subgroup of age associated with the star PW Andromedae, with an age of 30-80 million years ago, right on the edge of the stage of planetary formation. The detailed study of the stars of this subset may therefore complete knowledge of the stage of planetary formation in the solar-type stars cold. As for the second point, it has been shown that there is a clear relationship between the emission at different lines cromosféricas in the optical range and it has been determined that relationship. It has also been shown that the infrared triplete calcium is an excellent indicator of the magnetic activity in the stars cold. On the other hand, the relationship between the emission in this and the line has is able to distinguish between the stars presenting flares and other objects. Finally, the study of the relationship between activity and rotation, age appears to be an influential factor in their dispersion and should be taken into account in future studies.