Dissertation/Thesis Abstract

Topics of Galactic Structure and Stellar and Chemical Evolution
by Dominguez, Julio Cesar Chaname, Ph.D., The Ohio State University, 2005, 301; 10834951
Abstract (Summary)

In this thesis I explore current problems of Galactic astronomy by following two distinct but complementary approaches: the kinematic and photometric properties of local stellar populations, and the theory of stellar evolution. Under the first approach, I construct the largest available catalog of genuine wide binaries (a > 100 AU) and, using the relative positions of both components on a reduced proper-motion diagram, I cleanly classify them as belonging to either the disk or the halo of the Galaxy. These samples, drawn from the Revised New Luyten Two-Tenths catalog, are complete to separations of 500 and 900 arcsec, corresponding to about 0.1 and 1 parsec, respectively. At wide separations, both distributions are well described by power laws that have, within the uncertainties, identical exponents. The fact that these distributions have similar slopes and normalizations, despite the radically different Galactic environments to which they belong today, argues for similarity of the star-formation conditions of the two populations. The fact that the halo binaries obey a single power law out to about 1 parsec permits strong constraints on halo dark-matter candidates. Using Monte Carlo simulations, we exclude a halo fully composed of MAssive Compact Halo Objects (MACHOs) more massive than 43 solar masses at 95 percent confidence. I outline the prospects for using the Sloan Digital Sky Survey in the assembly of a catalog of halo wide binaries which, by improving the statistics at large separations, will enable exploration of MACHO masses in the astrophysically important regime of heavy stellar remnants. Finally, taking advantage of the identification of faint companions of Hipparcos stars, I construct a catalog of 424 intrinsically dim (i.e., low-mass) field stars with accurate (better than 3-sigma) parallaxes. Under the approach of stellar evolution, I study the long-standing problem of abundance anomalies in red giants, concentrating in non-standard mixing processes induced by stellar rotation. Unlike most previous work, I focus on the simultaneous reproduction of the CNO abundances in both Population I and Population II giants using the same physics and models. This novel approach led to a powerful new insight on one of the most difficult problems of astrophysics: the interplay between convection and rotation in stellar envelopes.

Indexing (document details)
Advisor: Gould, Andrew
School: The Ohio State University
Department: Astronomy
School Location: United States -- Ohio
Source: DAI-B 79/09(E), Dissertation Abstracts International
Subjects: Astronomy
Keywords: Binaries, Extra mixing, Halo, Proper-motion, Rgb, Stars
Publication Number: 10834951
ISBN: 9780355947939
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