In this dissertation we present a study of the B and Be star populations of the Double Cluster h and chi Persei. Classical Be stars are best known for their circumstellar disks, which are composed of material ejected off of the stellar surface during outburst events. These open clusters present an optimal location for studying the physical properties and variability of these disk structures, as upwards of 30% of the brightest B--type stars in h and chi Per are known to be Be stars. To begin our study, we first need to establish reliable measurements of basic physical parameters for each B--type and Be star in our sample. Blue optical spectroscopy is used to first measure projected rotational velocity, V sin i, effective surface temperature, Teff, and surface gravity, log g, for B--type sample stars, while available Stromgren photometry is used to calculate Teff and log g for the Be stars showing emission. Stellar masses and radii are then determined for each star via the evolutionary tracks of Schaller et al. [1992]. With these measurements, the model B--type star spectral energy distributions of Lanz & Hubeny [2007], and photometric observations in the optical, near-- and mid--IR wavelengths, we then use two independent means of determining the distance to each star, and compare these to the established cluster distances from the study of Currie et al. [2010]. This serves as a check of the reliability of our parameter determinations and our ability to model the total stellar flux of these B--type stars. Our study of the cluster Be stars is continued by examining the disk spectral energy distributions via photometric observations from WEBDA, 2MASS, Spitzer, AKARI, and WISE. Using the methods we have developed for modeling B star stellar flux, we can now extract the Be disk contribution to the total system flux. We also present multiple observations of Halpha taken between 2009--2012 with the KPNO Coude Feed, KPNO 2.1m, and WIRO telescopes, used to monitor the presence of disk emission and its strength in our sample Be stars. We use the Halpha equivalent width model of Grundstrom & Gies [2006] and the infrared flux model of Touhami et al. [2011] to constrain the disk masses, radii, and densities for our Be star sample. We find that our sample Be stars have disks 10--100 RSun in size, have densities typical of other observed Be disks, and that nearly all exhibit some level of variability in the size and strength of their disks over the course of our observations.

Star clusters are important to many areas of astronomy, and as the basic building blocks of galaxies, they can be used as key diagnostic tools within a wide range of disciplines in astrophysics. Star cluster populations are powerful tracers of the formation, assembly and evolutionary history of their parent galaxies. Although their importance has been recognised for decades, only in recent years has this area seen a major investment in time and effort. IAU Symposium 266 consolidates the expertise of leading researchers from a variety of topical subfields in astrophysics, to provide a comprehensive presentation of cutting-edge developments in theory, observations and simulations of star clusters and star cluster systems across a range of sizes and epochs. This volume gives an account of this forefront research, answering fundamental questions that will improve our understanding of numerous related issues and show how this field will take its next major step forward.

A well-illustrated historical survey of the science of measuring the brightness and colours of stars - for professional astronomers, amateur astronomers and historians of science.

The Nebular Variables focuses on the nebular variables and their characteristics. Discussions are organized by type of nebular variable, namely, RW Aurigae stars, T Orionis stars, T Tauri stars, and peculiar nebular objects. Topics range from light variations of the stars to their spectroscopic and physical characteristics, spatial distribution, interaction with nebulosity, and evolutionary features. This volume is divided into four sections and consists of 25 chapters, the first of which provides general information on nebular variables, including their stellar associations and their classification into three distinct groups: RW Aurigae, T Orionis and T Tauri variables. These three groups of nebular variables are examined in more detail in the chapters that follow in terms of their light variations, spatial distribution, interaction with nebulosity, and spectroscopic, physical, and evolutionary characteristics. Visual and photoelectric light curves, mass loss determined spectroscopically, luminosities, and stellar radii are considered. The book also explores the possibility that some of the nebulae associated with certain nebular variables have evolved from a protoplanetary disc of material consisting of both gas and solid matter. Peculiar nebular variables such as the long period variable R Aquarii, Herbig-Haro objects, symbiotic variables, and infrared stars are analyzed as well. This book is written primarily for students and teachers of astronomy.