No description available.

We present a detailed analysis of the white dwarf luminosity functions derived from the local 40 pc sample and the deep proper motion catalog of Munn et al. Many previous studies have ignored the contribution of thick disk white dwarfs to the Galactic disk luminosity function, which results in an erroneous age measurement. We demonstrate that the ratio of thick/thin disk white dwarfs is roughly 20% in the local sample. Simultaneously fitting for both disk components, we derive ages of 6.8-7.0 Gyr for the thin disk and 8.7 +/- 0.1 Gyr for the thick disk from the local 40 pc sample. Similarly, we derive ages of 7.4-8.2 Gyr for the thin disk and 9.5-9.9 Gyr for the thick disk from the deep proper motion catalog, which shows no evidence of a deviation from a constant star formation rate in the past 2.5 Gyr. We constrain the time difference between the onset of star formation in the thin disk and the thick disk to be 1.6(-0.4)(+0.3) Gyr. The faint end of the luminosity function for the halo white dwarfs is less constrained, resulting in an age estimate of 12.5(-3.4)(+1.4) Gyr for the Galactic inner halo. This is the first time that ages for all three major components of the Galaxy have been obtained from a sample of field white dwarfs that is large enough to contain significant numbers of disk and halo objects. The resultant ages agree reasonably well with the age estimates for the oldest open and globular clusters.

No description available.

A catalog of 8472 white dwarf (WD) candidates is presented, selected using reduced proper motions from the deep proper motion catalog of Munn et al. Candidates are selected in the magnitude range 16 < r < 21.5 over 980 square degrees, and 16 < r < 21.3 over an additional 1276 square degrees, within the Sloan Digital Sky Survey (SDSS) imaging footprint. Distances, bolometric luminosities, and atmospheric compositions are derived by fitting SDSS ugriz photometry to pure hydrogen and helium model atmospheres (assuming surface gravities log g = 8). The disk white dwarf luminosity function (WDLF) is constructed using a sample of 2839 stars with 5.5 < M-bol < 17, with statistically significant numbers of stars cooler than the turnover in the luminosity function. The WDLF for the halo is also constructed, using a sample of 135 halo WDs with 5 < M-bol < 16. We find space densities of disk and halo WDs in the solar neighborhood of 5.5 +/- 0.1 x 10(-3) pc(-3) and 3.5 +/- 0.7 x 10(-5) pc(-3), respectively. We resolve the bump in the disk WDLF due to the onset of fully convective envelopes in WDs, and see indications of it in the halo WDLF as well.

<p>This diploma thesis presents a preliminary study of the ratio of branching ratio r = BR(η → 3π⁰) / BR(η → π⁺ π^-π⁰). The experimental data used is collected by WASA-at-COSY which is a 4π sr detector optimised to detect light mesons and their decay products and is situated in Jülich, Germany.The focus of the work is to see how different reconstruction methods for the detected particles can alter both the measured values of the  branching ratios and the luminosity dependence of these branching ratios. The results show that for some of the methods, the measured branching ratios have a clear luminosity dependence. Depending on method, the extracted branching ratios vary differently. A few different methods have been studied, so the results provides a qualitative understanding of the behaviour of the measured branching ratios for different luminosities.</p>

White dwarfs are the final remnants of low- and intermediate-mass stars. About 95% of main- sequence stars will end their evolutionary pathways as white dwarfs and, hence, the study of the white dwarf population provides details about the late stages of the life of the vast majority of stars.Since white dwarfs are long-lived objects, they also constitute useful objects to study the structure and evolution of our Galaxy. For instance, the initial-final mass relationship, which connects the final mass of a white dwarf with the initial mass of its main-sequence progenitor, is of paramount importance for different aspects in modern astrophysics. This function is used for determining the ages of globular clusters and their distances, for studying the chemical evolution of galaxies, and also to understand the properties of the Galactic population of white dwarfs. Despite its relevance, this relationship is still relatively poorly constrained.The main aim of this thesis is the study of the initial-final mass relationship. For such purpose we have used two different approaches. From an observational perspective, the statistical significance of the current initial final mass relationship can be improved by performing spectroscopic observations of white dwarfs for which some important parameters are available. Since this approach involves the use of theoretical stellar evolutionary tracks the resulting initial-final mass relationship is, in fact, semi-empirical. In this thesis we present a promising method which consists in using common proper motion pairs comprised of a white dwarf and a FGK star. It is sound to assume that the members of the system were born simultaneously and with the same chemical composition. Moreover, these stars are well separated and it can be considered that they have evolved as isolated stars, since mass exchange between them is unlikely. Thus, a careful analysis of the observational data of both members of each pair allows us to derive the initial and final masses of the white dwarf components, something which is totally impossible when white dwarfs are isolated. Considering the new data that we have obtained with this work and the observational data currently used to define the initial-final mass relationship we have carried out a revision of this relationship, giving some clues on its dependence on different parameters, especially on metallicity.The second approach to improve the initial-final mass relationship involves an indirect measurement, which has been carried out by studying its influence on one of the powerful tools related to the white dwarf population, the white dwarf luminosity function. We have computed a series of luminosity functions using different theoretical initial-final mass relationships, and also, considering the semi-empirical relation derived in this thesis. We have compared these computations with the available observational data in order to evaluate the validity of each of these relations.In order to increase the statistical significance of the white dwarf luminosity function and to improve the initial-final mass relationship it is necessary to extend the amount of accurate and reliable observational data. For this reason part of the thesis is devoted to the Alhambra Survey, which is a good example of the new deep surveys currently under development. These observational projects will detect thousands of new white dwarfs, some of them belonging to common proper motion pairs, which could be eventually used to extend our analysis. Thus, we have performed an exhaustive study to optimize the identification procedure of the white dwarf candidates which will be eventually detected by the Alhambra survey.

This diploma thesis presents a preliminary study of the ratio of branching ratio r = BR(η → 3π0) / BR(η → π+ π- π0). The experimental data used is collected by WASA-at-COSY which is a 4π sr detector optimised to detect light mesons and their decay products and is situated in Jülich, Germany.The focus of the work is to see how different reconstruction methods for the detected particles can alter both the measured values of the  branching ratios and the luminosity dependence of these branching ratios. The results show that for some of the methods, the measured branching ratios have a clear luminosity dependence. Depending on method, the extracted branching ratios vary differently. A few different methods have been studied, so the results provides a qualitative understanding of the behaviour of the measured branching ratios for different luminosities.

Thesis (Ph. D.)--University of Hawaii at Manoa, 1995. / Includes bibliographical references (leaves 106-112). / Microfiche. / x, 112 leaves, bound ill. (some col.) 29 cm

Thesis (Ph. D.)--University of Hawaii at Manoa, 2004. / Includes bibliographical references. / Also available by subscription via World Wide Web / xxxiii, 335 leaves, bound ill. 29 cm

Thesis (Ph. D.)--University of Hawaii at Manoa, 2004. / Includes bibliographical references.