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NASA NTRS2004

The X-ray halo of an extremely luminous LSB disk galaxy

We are continuing to refine our upper limit on emission from halo gas in Malin 2. The upper limit is, of course, below the detected flux, but is made more difficult to quantify by the disk and possible AGN sources. We are also exploring spectral and spatial-size constraints to help separate the sources of emission. On the theory side, more recent work on the X-ray halo luminosity from halo gas leftover from galaxy formation has lowered the prediction for disk galaxies (e.g. Toft et al. 2002, MNRAS, 335, 799). While our upper limit is well below the original prediction, refinements in model have moved the theoretical goalposts, so that the observation may be consistent with newer models. A recent theoretical development, which our observations of Malin 2 appear to support, is that a substantial amount of mass can be accreted onto galaxies without being heated at a virial shock. The previous standard theory was that gas accreting into a halo hits a virial shock and is heated to high temperatures, which could produce X-ray halos in massive galaxies. Recent models show that "smooth accretion" of matter bypasses the virial shocking (Murali e t al. 2002, ApJ, 571, 1; Birnboim & Dekel 2003, MNRAS, 345, 349). Additionally, new hydrodynamical simulations of galaxy mergers by UCSC graduate student T. J. Cox show that hot gas halos can be created by gas blown out from the merger, taking up orbital energy of the merging galaxies (Cox et al. 2004, ApJ, 607, L87). If mergers rather than virial shocking are the origin of hot gas halos, the existence of an X-ray halo should depend more on past merger activity than halo mass. Then it makes sense that elliptical galaxies and poor groups with ellipticals, which are probably formed in mergers, have X-ray gas halos; while a giant, quiescent LSB disk galaxy like Malin 2, which has never suffered a major merger, does not have an X-ray halo. While both the observational expectations and theoretical models have changed since we began this project, which has forced us to re-evaluate the goals, we are pressing forward to firm up the observations and put them in context of the current models for X-ray halos of massive galaxies.

Weiner, Benjamin J.↗

NASA NTRS1983

Mesopheric turbulence intensities measured with a HF radar at 35 deg S. Part 2

A theory was developed for extracting turbulence energy dissipation rates from spectra measured with a radar. It is shown that factors apart from turbulence contribute to the observed spectral widths, and that these factors must be considered if accurate estimates of energy dissipation rates are to be obtained. In particular, beam-width broadening and shear broadening are important. The first results obtained with this theory are presented. The rules were obtained using the large HF array at Adelaide, Australia, primarily during the Southern Hemisphere winter of 1981. Results are consistent with rocket measurements of turbulence, with typical values varying between 0.01 and 1/0.2 W kg at 80-90 km altitude.

Hocking, W. K.↗

NASA NTRS1982

Thermal fluctuations and the diffuse electrostatic emissions

The suggestion that the weak-banded electrostatic emissions observed in the magnetosphere at frequencies between the electron gyrofrequency and upper hybrid frequency are thermal fluctuations is quantitatively explored, by means of a hot-cold model for dayside electron distributions with density and temperature ratios much greater than unity. It is determined that, for typical dayside conditions, the observed waves are weakly damper Bernstein-Harris modes whose spectral density and polarization, perpendicular to the ambient magnetic field, can be accounted for by the theory. It is suggested that the formalism developed may be applicable to weak electron cyclotron emissions at Jupiter and Saturn, and can be extended to lower-frequency ion cyclotron fluctuations by modifying the theory to include ion contributions.

Sentman, D. D.↗

NASA NTRS1999

Characterization of Sound Radiation by Unresolved Scales of Motion in Computational Aeroacoustics

Evaluation of the sound sources in a high Reynolds number turbulent flow requires time-accurate resolution of an extremely large number of scales of motion. Direct numerical simulations will therefore remain infeasible for the forseeable future: although current large eddy simulation methods can resolve the largest scales of motion accurately the, they must leave some scales of motion unresolved. A priori studies show that acoustic power can be underestimated significantly if the contribution of these unresolved scales is simply neglected. In this paper, the problem of evaluating the sound radiation properties of the unresolved, subgrid-scale motions is approached in the spirit of the simplest subgrid stress models: the unresolved velocity field is treated as isotropic turbulence with statistical descriptors, evaluated from the resolved field. The theory of isotropic turbulence is applied to derive formulas for the total power and the power spectral density of the sound radiated by a filtered velocity field. These quantities are compared with the corresponding quantities for the unfiltered field for a range of filter widths and Reynolds numbers.

Rubinstein, Robert↗

NASA NTRS2002

Observations and Laboratory Data of Planetary Organics

Many efforts are underway to search for evidence of prebiotic materials in the outer solar system. Current and planned Mars missions obtain remote sensing observations that can be used to address the potential presence of prebiotic materials. Additional missions to, and continuing earth-based observations of, more distant solar system objects will also provide remote sensing observations that can be used to address the potential presence of prebiotic materials. I will present an overview of on-going observations, associated laboratory investigations of candidate materials, and theoretical modeling of observational data. In the past the room temperature reflectance spectra of many residues created from HC-bearing gases and solids have been reported. The results of an investigation of what effect temperatures more representative of outer solar system surfaces (50-140K) have on the reflectance spectra of these residues, and the associated interpretations, will be presented. The relatively organic-rich Tagish Lake Meteorite has been suggested as a spectral analog for Dtype asteroids. Using a new approach that relies upon iterative use of Hapke theory and Kraniers-Kronig analysis the optical constants of TLM were estimated. The approach and results of the analysis will be presented. Use of optical constants in scattering theories, such as the Hapke theory, provide the ability to determine quantitative estimates of the relative abundances and grain sizes of candidate surface components. This approach has been applied to interpret the reflectance spectra of several outer solar system surfaces. A summary will be provided describing the results of such modeling efforts.

Roush, Ted L.↗

NASA NTRS1973

Inelastic Light Scattering Processes

Five different inelastic light scattering processes will be denoted by, ordinary Raman scattering (ORS), resonance Raman scattering (RRS), off-resonance fluorescence (ORF), resonance fluorescence (RF), and broad fluorescence (BF). A distinction between fluorescence (including ORF and RF) and Raman scattering (including ORS and RRS) will be made in terms of the number of intermediate molecular states which contribute significantly to the scattered amplitude, and not in terms of excited state lifetimes or virtual versus real processes. The theory of these processes will be reviewed, including the effects of pressure, laser wavelength, and laser spectral distribution on the scattered intensity. The application of these processes to the remote sensing of atmospheric pollutants will be discussed briefly. It will be pointed out that the poor sensitivity of the ORS technique cannot be increased by going toward resonance without also compromising the advantages it has over the RF technique. Experimental results on inelastic light scattering from I(sub 2) vapor will be presented. As a single longitudinal mode 5145 A argon-ion laser line was tuned away from an I(sub 2) absorption line, the scattering was observed to change from RF to ORF. The basis, of the distinction is the different pressure dependence of the scattered intensity. Nearly three orders of magnitude enhancement of the scattered intensity was measured in going from ORF to RF. Forty-seven overtones were observed and their relative intensities measured. The ORF cross section of I(sub 2) compared to the ORS cross section of N2 was found to be 3 x 10(exp 6), with I(sub 2) at its room temperature vapor pressure.

Fouche, Daniel G.↗

NASA NTRS1987

A spectral view of nonlinear fluxes and stationary-transient interaction in the atmosphere

Nonlinear spectral transfers of kinetic energy and enstrophy, and stationary-transient interaction, are studied using global FGGE data for January 1979. The spectral transfers are found to be dominated by two dynamically distinct components, one due to nonlinear self-interactions within the transient flow and the other arising from coupled interactions between the stationary and transient parts of the flow. The former seems to be attributable to two-dimensional homogeneous turbulence, while the second cannot be understood within that theory. It is argued that the mixed stationary-transient interactions can be understood physically as a process of shear-induced spectral transfer of transient enstrophy along lines of constant zonal wavenumber. The transients act mainly to strengthen the stationary flow, and this 'forcing' operates on a timescale comparable to presumed viscous timescales.

Shepherd, Theodore G.↗

NASA NTRS1988

Solar oscillations instrumentation and measurement theory

Solar-oscillation instruments are reviewed. Common characteristics include detecting solar radial velocities on Fraunhofer lines with a 2-point measuring technique, high spectral resolution and stability, etc. The choice of the spectral line for getting a high signal to solar noise ratio is addressed. Velocity imaging of solar oscillations modes is detailed, including spatial sampling and span, highest observable degree. Applications of these different analyses is applied to existing or future helioseismology instruments.

Appourchaux, T.↗

NASA NTRS1992

The three-point function in an ensemble of numerical simulations

The three-point function in Fourier space is evaluated for an ensemble of 2D numerical simulations with nine initial power spectra distinguished by spectral index and cutoff. To remove the main dependences on scale and time, results are presented as the reduced amplitude Q in the hierarchical model. To lowest nonvanishing order in perturbation theory, Q is a constant, independent of length scale, of time, and of initial spectrum. The results show that in the nonlinear regime of evolution, normalizing to Q does remove the main variations, but systematic dependences on spectral index and cutoff remain at late times that depend on properties of the initial spectrum. Models with initial power cut off on a scale that has been evolved far into the nonlinear regime are indistinguishable from models with no cutoff.

Fry, J. N.↗

NASA NTRS1975

A digital algorithm for spectral deconvolution with noise filtering and peak picking: NOFIPP-DECON

Noise-filtering, peak-picking deconvolution software incorporates multiple convoluted convolute integers and multiparameter optimization pattern search. The two theories are described and three aspects of the software package are discussed in detail. Noise-filtering deconvolution was applied to a number of experimental cases ranging from noisy, nondispersive X-ray analyzer data to very noisy photoelectric polarimeter data. Comparisons were made with published infrared data, and a man-machine interactive language has evolved for assisting in very difficult cases. A modified version of the program is being used for routine preprocessing of mass spectral and gas chromatographic data.

Edwards, T. R.↗

NASA NTRS1976

Photometric properties of the surface of Io and their influence on line formation in the atmosphere

The paper presents a quantitative theory of line formation in an atmosphere above a surface with backscattering properties. Sufficiently high spatial and spectral resolution spectra of resonance lines in Io region A can yield data on the surface scattering properties as well as the number density of scattering molecules. Macroscopically homogeneous models of scattering from the surface of Io are discussed, and it is concluded that multiple reflection from crystal facets is the most likely cause for the observed geometric albedo and phase variation.

Yung, Y. L.↗

NASA NTRS1976

Solar heating in the Mars dusty atmosphere

The complex refractive index in the solar spectral region is estimated. With this index and the size distribution estimated from the UVS data Mie theory is used to compute the radiative parameters required for including radiative scattering in simplified radiative transfer approximations. These approximations then enable the wavelength-integrated solar heating to be computed for various dust-laden Martian atmospheres. The calculations presented in the main body of the paper were computer using the delta-Eddington approximation.

Zurek, R. W.↗

NASA NTRS1981

Far-infrared bandpass filters from cross-shaped grids

The optical transmission characteristics of electroformed metal grids with inductive and capacitive cross patterns have been investigated in the far-infrared spectral region. The transmission characteristics of one- and two-grid devices are represented by transmission line theory parameters. Results are used to suggest construction guidelines for two-grid bandpass filters.

Tomaselli, V. P.↗

NASA NTRS1990

Numerical simulation of transition in a rotating disk flow

An investigation of the laminar-turbulence transition process in a three-dimensional boundary layer on a rotating disk is initiated. Preliminary results from a direct numerical simulation using spectral collocation method are presented. The simulation results in the linear regime is tested against linear stability theory. Saturation of the primary disturbance energy suggests the importance of modal interaction in initiating transition.

Balachandar, S.↗

NASA NTRS2022

The Polstar High Resolution Spectropolarimetry MIDEX Mission

The Polstar mission will provide a space-borne 60 cm spectropolarimeter operating at ultraviolet (UV) wavelengths, capturing all four Stokes parameters (intensity, two linear polarization components, and circular polarization). Polstar’s capabilities are designed to meet its goal of determining how circumstellar gas flows alter and inform massive star evolution, affect the stellar remnant population, and stir and enrich the interstellar medium (ISM). These will be achieved by investigating the dynamical geometries in the winds and disks of hot stars, the composition and magnetic alignment of interstellar dust, and the star-forming accretion disks of UV-bright stars at an important transition boundary. Together these areas map out a kind of two-way interface between massive stars and their effect on our galaxy, wherein the stellar winds enrich the ISM with metals and kinetic energy, preconditioning their environment and the stellar endpoints prior to undergoing supernova. The ISM dust in turn reveals the composition and magnetic environment leading to new star formation, and the accretion disks of Herbig Ae/Be stars reveal how the ISM gas returns to make new massive stars. Polstar will combine high-resolution spectroscopy in the time domain with high-precision UV polarimetry. Doppler-shifted UV resonance line opacity will provide information about circumstellar kinematics, while polarization gives complementary geometric information about unseen structures. The composition and magnetic alignment of the smallest interstellar dust grains provides a probe of the ISM utilizing radiative alignment theory (RAT). Polstar will operate in the far-UV (FUV) at 122–200 nm at high spectral resolution of around R ∼ 30k, and at FUV and near-UV (NUV) wavelengths of 122–320 nm at lower spectral resolutions of 0.1 - 1k. Detection of polarization levels as weak as 0.1% are expected, with a temporal cadence ranging from 5–10 minutes for most wind variability studies, to hours or days for sampling rotation, to days or weeks for sampling binary orbits, to months to a year for sampling substructure in the inner regions of protoplanetary disks. Sub-meter-class aperture is well suited to access this wide array of time domain science, made possible by restricting to a few hundred bright, massive stars, necessarily extincted by a small to moderate column of interstellar dust, informing both the attributes of the stars and the ISM through which they are seen. As such, the focus is on our own galaxy and its evolutionary drivers, but a few targets in the Magellanic clouds offer the potential to extend this understanding to low-metallicity environments.

Paul A Scowen↗

NASA NTRS1985

The application of contraction theory to an iterative formulation of electromagnetic scattering

Contraction theory is applied to an iterative formulation of electromagnetic scattering from periodic structures and a computational method for insuring convergence is developed. A short history of spectral (or k-space) formulation is presented with an emphasis on application to periodic surfaces. To insure a convergent solution of the iterative equation, a process called the contraction corrector method is developed. Convergence properties of previously presented iterative solutions to one-dimensional problems are examined utilizing contraction theory and the general conditions for achieving a convergent solution are explored. The contraction corrector method is then applied to several scattering problems including an infinite grating of thin wires with the solution data compared to previous works.

Brand, J. C.↗

NASA NTRS1975

Comparison of theory and experiment for homogeneous turbulence with shear

Solutions for uniformly-sheared turbulence, in which the interaction of the turbulence with the mean shear dominates the turbulent self-interaction, are compared with experiment. An anisotropic spectral tensor, which appears general enough to represent the initial experimental turbulence, is used for the initial condition in the calculations. The evolution of one-point turbulence components and microscales, as well as two-point velocity correlations, are considered. In most cases the agreement with experiment is good. The theory correctly predicts the presence of a negative region for two-point longitudinal-velocity correlations only for point separations in the direction normal to the flow and the mean gradient.

Deissler, R. G.↗

NASA NTRS1991

Vertical tilts of tropospheric waves - Observations and theory

Two methods are used to investigate the vertical tilts of planetary waves as functions of zonal wavenumber and frequency. The vertical tilts are computed by cross-spectral analysis of the geopotential heights at different pressures. In the midlatitude troposphere, the eastward-moving waves had a westward tilt with height, as expected, but the westward-moving waves with frequencies higher than 0.2/d showed statistically significant eastward vertical tilts. For a free Rossby wave, this implies that the Eliassen-Palm flux is downward along with its energy propagation. A downward energy propagation suggests an upper-level source of these waves. It is proposed that the eastward-tilting waves were forced by the nonlinear interaction of stationary waves and baroclinically unstable cyclone-scale waves. The predicted vertical tilt and phase speed were consistent with the observations. In addition, simulations of a general circulation model were analyzed. In the control run, eastward-tilting waves disappeared when the sources of stationary waves were removed. This is consistent with the present theory.

Ebisuzaki, Wesley↗