Wolf-Rayet phenomena

The properties of stars showing Wolf-Rayet phenomena are outlined along with the direction of future work. Emphasis is placed on the characteristics of W-R spectra. Specifically the following topics are covered: the absolute visual magnitudes; the heterogeneity of WN spectra; the existence of transition type spectra and compositions the mass loss rates; and the existence of very luminous and possibly very massive W-R stars. Also, a brief overview of current understanding of the theoretical aspects of stellar evolution and stellar winds and the various scenarios that have been proposed to understand W-R spectra are included

Mass-loss rates from early-type stars

The mass loss rates are derived for a number of unevolved O-type stars and a few WN stars from high dispersion IUE spectra of their P Cygni profiles. When combined with other published mass loss rates, it is found that the relationship between log m and M sub BOL is a broad band rather than a linear relation, suggesting that the line radiation driven wind theory may not be sufficient to explain mass loss. The mass loss rates for the WN stars, while more uncertain, confirm that these stars lose mass about 100 times faster than O-stars

Spectroscopic observations of selected stellar systems

Spectra of very luminous, high temperature stars, the o-type stars with the largest masses among stars, and the Wolf-Rayet (W-R) stars are studied. These stars are characterized by strong stellar winds which produce signiicant mass loss. The nature and evolution of these winds are studied to learn the densities, velocity structue, ionization balance, and composition. The IUE satellite provides the best way to study these phenomena because many of the most important ground state and excited state lines of common highly ionized species are found in the spectral range

The Stellar Content of Obscured Galactic Giant H II Regions: II. W42

We present near infrared J, H, and K images and K-band spectroscopy in the giant HII region W42. A massive star cluster is revealed; the color-color plot and K-band spectroscopic morphology of two of the brighter objects suggest the presence of young stellar objects. The spectrum of the bright central star is similar to unobscured stars with MK spectral types of O5-O6.5. If this star is on the zero age main sequence, then the derived spectrophotometric distance is considerably smaller than previous estimates. The Lyman continuum luminosity of the cluster is a few times that of the Trapezium. The slope of the K-band luminosity function is similar to that for the Trapezium cluster and significantly steeper than that for the massive star cluster in M17 or the Arches cluster near the Galactic center.Comment: 30 pages, 11 figures, late

Solvable Lie algebras are not that hypo

We study a type of left-invariant structure on Lie groups, or equivalently on Lie algebras. We introduce obstructions to the existence of a hypo structure, namely the 5-dimensional geometry of hypersurfaces in manifolds with holonomy SU(3). The choice of a splitting g^*=V_1 + V_2, and the vanishing of certain associated cohomology groups, determine a first obstruction. We also construct necessary conditions for the existence of a hypo structure with a fixed almost-contact form. For non-unimodular Lie algebras, we derive an obstruction to the existence of a hypo structure, with no choice involved. We apply these methods to classify solvable Lie algebras that admit a hypo structure.Comment: 21 pages; v2: presentation improved, typos corrected, notational conflicts eliminated. To appear in Transformation Group

Exchange-correlation potential for Current Density Functional Theory of frequency dependent linear response

The dynamical, long-wavelength longitudinal and transverse exchange-correlation potentials for a homogeneous electron gas are evaluated in a microscopic model based on an approximate decoupling of the equation of motion for the current-current response function. The transverse spectrum turns out to be very similar to the longitudinal one. We obtain evidence for a strong spectral structure near twice the plasma frequency due to a two-plasmon threshold for two-pair excitations, which may be observable in inelastic scattering experiments. Our results give the entire input needed to implement the Time-Dependent Current Density Functional Theory scheme recently developed by G. Vignale and W. Kohn [Phys. Rev. Lett. 77, 2037 (1996)] and are fitted to analytic functions to facilitate such applications.Comment: 6 pages, 3 figure

On the generation and the nonlinear dynamics of X-waves of the Schroedinger equation

The generation of finite energy packets of X-waves is analysed in normally dispersive cubic media by using an X-wave expansion. The 3D nonlinear Schroedinger model is reduced to a 1D equation with anomalous dispersion. Pulse splitting and beam replenishment as observed in experiments with water and Kerr media are explained in terms of a higher order breathing soliton. The results presented also hold in periodic media and Bose-condensed gases.Comment: 18 pages, 6 figures, corrected version to be published in Physical Review

The Money Chase: How Proposed Changes to Campaign Finance Laws Could Impact Female Candidates

In their book, Madam President: Shattering the Last Glass Ceiling, Eleanor Clift and Tom Brazaitis shed light on the various reasons why a woman has yet to ascend the political ladder and occupy the Oval Office. While the authors do include some mention of female candidates\u27 difficulty with fundraising, the authors fail to address a key component of any political analysis: Campaign finance reform. Reforming the federal election laws could have a profound influence on the prospects of current and future female politicians. Two reform proposals, including banning or restricting soft money and banning or restricting the practice of bundling, have consistently appeared on the short list of suggested changes to campaign finance laws. This Book Review explores these reform proposals and explains why banning soft money or bundling would take away two essential sources of campaign funds for women, thereby hindering their ability to rise through the political ranks