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Aerospace, Physics, and Space Science Faculty Publications

Series

1998

Articles 1 - 8 of 8

Full-Text Articles in Physical Sciences and Mathematics

Time Series Energy Production In Smoothed Particle Hydrodynamics Accretion Disks: Superhumps In The Am Canum Venaticorum Stars, James C. Simpson, Matt A. Wood Oct 1998

Time Series Energy Production In Smoothed Particle Hydrodynamics Accretion Disks: Superhumps In The Am Canum Venaticorum Stars, James C. Simpson, Matt A. Wood

Aerospace, Physics, and Space Science Faculty Publications

The energy production time series of our purely hydrodynamic accretion disk simulations display remarkable similarities with the observed light curves of dwarf novae superhumps in general and the AM CVn stars in particular. The superhump period excess as a function of mass ratio agrees well with earlier theoretical and numerical results, and the amplitudes and relative phases of the harmonics in the power spectra agree well with the observations. The morphology of the mean pulse profile appears to be a useful predictor of system mass ratio. Our modified smoothed particle hydrodynamics code time symmetrizes the interparticle forces when individual time …

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Broadband Optical Observations Of Bl Lacertae During The 1997 Outburst, Terry D. Oswalt, Daniel Marshall, Tim Robishaw Jun 1998

Broadband Optical Observations Of Bl Lacertae During The 1997 Outburst, Terry D. Oswalt, Daniel Marshall, Tim Robishaw

Aerospace, Physics, and Space Science Faculty Publications

We present BVRI observations of BL Lacertae during its recent outburst. These observations, made during a 3 month period, cover a significant portion of the optical flare. The reduced data are displayed as light curves and broadband spectra. Changes in the spectral index are analyzed, and the results are compared with previous BL Lac observations. We find that the variations are simultaneous in the optical bands, but the higher frequency bands show a higher amplitude of variability. The spectral index is variable during the active period, and there is marginal evidence that the spectrum flattens as the source gets brighter.

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White Dwarf Cosmochronometry. I. Monte Carlo Simulations Of Proper-Motion And Magnitude-Limited Samples Using Schmidt's 1/Vmax Estimator, Matt A. Wood, Terry D. Oswalt Apr 1998

White Dwarf Cosmochronometry. I. Monte Carlo Simulations Of Proper-Motion And Magnitude-Limited Samples Using Schmidt's 1/Vmax Estimator, Matt A. Wood, Terry D. Oswalt

Aerospace, Physics, and Space Science Faculty Publications

Observationally, white dwarf stars are a remarkably homogeneous class with a minimum observed Teff ∼ 4000 K. Theoretically, the physics that determines their cooling timescales is relatively more straightforward than that which determines main-sequence evolutionary timescales. As a result, the white dwarf luminosity function has for the last decade been used as a probe of the age and star formation rate of the Galactic disk, providing an estimated local disk age of ∼ 10 Gyr with estimated total uncertainties of roughly 20%. A long-standing criticism of the technique is that the reality of the reported downturn in the luminosity function …

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Asteroseismology Of A Star Cooled By Neutrino Emission: The Pulsating Pre-White Dwarf Pg 0122 + 200, Marlea Sean O'Brien, Matt A. Wood Mar 1998

Asteroseismology Of A Star Cooled By Neutrino Emission: The Pulsating Pre-White Dwarf Pg 0122 + 200, Marlea Sean O'Brien, Matt A. Wood

Aerospace, Physics, and Space Science Faculty Publications

Observation of g-rnode pulsations in the variable pre-white dwarf (GW Virginis) stars provides a unique means to probe their interiors and to study the late stages of stellar evolution. Multisite campaigns have in several cases proved highly successful in decoding pre-white dwarf light curves. Three previous attempts to untangle the pulsation spectrum of the coolest GW Virginis star, PG 0122+200, confirmed the existence of multiple g-modes but left the fundamental period spacing and therefore the star's mass and luminosity in doubt. We present an analysis based on new observations of PG 0122+200 obtained during a Whole Earth Telescope (WET) campaign …

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Understanding The Cool Da White Dwarf Pulsator, G29-38, Scot J. Kleinman, Matt A. Wood Mar 1998

Understanding The Cool Da White Dwarf Pulsator, G29-38, Scot J. Kleinman, Matt A. Wood

Aerospace, Physics, and Space Science Faculty Publications

The white dwarfs are promising laboratories for the study of cosmochronology and stellar evolution. Through observations of the pulsating white dwarfs, we can measure their internal structures and compositions, critical to understanding post-main-sequence evolution, along with their cooling rates, which will allow us to calibrate their ages directly. The most important set of white dwarf variables to measure are the oldest of the pulsators, the cool DA variables (DAVs), which have not been explored previously through asteroseismology due to their complexity and instability. Through a time-series photometry data set spanning 10 yr, we explore the pulsation spectrum of the cool …

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Mach-Zehnder Interferometer Fringe Projector For Variable Resolution Video Moire, Phillip C. Kalmanson, August Schutte, Chris L. Hart, Joel H. Blatt Jan 1998

Mach-Zehnder Interferometer Fringe Projector For Variable Resolution Video Moire, Phillip C. Kalmanson, August Schutte, Chris L. Hart, Joel H. Blatt

Aerospace, Physics, and Space Science Faculty Publications

A Mach-Zehnder based variable resolution fringe projection system has been built for 3-D video moini machine vision. This system uses the three main advantages of the Mach-Zehnder - 1) There is no optical feedback to the laser source, 2) The interfemmeter can accept two different laser wavelengths simultaneously, and 3) The interferometer produces two orthngonal output beams. The lack of optical feedback makes the Mach-Zehnder especially attractive for use with high power laser diode sources which are sensitive to optical feedback. When the two input ports axe used with two different wavelength lasers, the target can be illuminated by simultaneous …

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Steps Toward Determination Of The Size And Structure Of The Broad-Line Region In Active Galactic Nuclei. Xii. Ground-Based Monitoring Of 3c 390.3, Matthias Dietrich, T. D. Oswalt, Jun Tao Jan 1998

Steps Toward Determination Of The Size And Structure Of The Broad-Line Region In Active Galactic Nuclei. Xii. Ground-Based Monitoring Of 3c 390.3, Matthias Dietrich, T. D. Oswalt, Jun Tao

Aerospace, Physics, and Space Science Faculty Publications

Results of a ground-based optical monitoring campaign on 3C 390.3 in 1994-1995 are presented. The broadband fluxes (B, V, R, and I), the spectrophotometric optical continuum flux Fλ(5177 Å), and the integrated emission-line fluxes of Hα, Hβ, Hγ, He II λ15876, and He II A4686 all show a nearly monotonic increase with episodes of milder short-term variations superposed. The amplitude of the continuum variations increases with decreasing wavelength (4400-9000 Å). The optical continuum variations follow the variations in the ultraviolet and X-ray with time delays, measured from the centroids of the cross-correlation functions, typically around 5 days, but with uncertainties …

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Multicolor Fringe Projection System With Enhanced 3-D Reconstruction Of Surfaces, Bernard S. Gilbert, Joel H. Blatt Jan 1998

Multicolor Fringe Projection System With Enhanced 3-D Reconstruction Of Surfaces, Bernard S. Gilbert, Joel H. Blatt

Aerospace, Physics, and Space Science Faculty Publications

Most optical topology systems use a single wavelength laser for projection, using a swept spot, a moving line, or a projected grating. In a typical projected grating system, the gratings are shifted and a series of images are used to recover the 3-D shape of the target. When the series of images is analyzed in the normal phase shift manner, the resulting 2-D phase map typically has phase unwrapping problems due to noise and Nyquist limits. Surfaces with large vertical discontinuities present the biggest problem in 3-D shape recovery. This paper looks at simultaneously projecting multiple wavelengths onto a surface …

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