Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “VISIBLE SPECTRA”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,387 records · Page 77
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Formation of Sodium and Potassium Nanoparticles upon Local Electron Bombardment of Alkali-Halide Crystals

It has been shown experimentally that upon local bombardment of NaCl, KCl, and KBr crystals with 50-keV electrons, sodium and potassium nanoparticles with plasmon resonances in the visible spectral region are formed in these crystals. We have obtained optical-density spectra of crystals after the bombardment with electrons in various doses. The probability of location of nanoparticles in the solid or liquid phase, as well as interference effects emerging in the irradiated zone of crystals, have been studied using numerical simulation.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Photoluminescence and Raman spectroscopy of wide bandgap semiconductors damaged by deep-UV laser irradiation

The effects of a pulsed, focused, deep-UV (4.66 eV) laser on wide and ultra-wide bandgap semiconductors were investigated with photoluminescence (PL) and Raman spectroscopy. Three semiconductor single crystals were studied: silicon carbide (6H-SiC), gallium nitride (GaN), and gallium oxide (β-Ga 2 O 3 ). Atomic emission lines from neutral Ga or Si were observed during the laser-damage process. For all three semiconductors, PL mapping (3.49 eV laser excitation) of the damaged material revealed visible emission bands in the 2.6–2.8 eV range, attributed to point defects. Raman spectra (2.33 eV excitation) showed a reduction in the Raman peak intensities in the damaged region, along with weak PL bands around 1.9–2.1 eV.

36 MATERIALS SCIENCE↗
DOE OSTI2016

QUASI-PERIODICITIES AT YEAR-LIKE TIMESCALES IN BLAZARS

We searched for quasi-periodicities on year-like timescales in the light curves of six blazars in the optical—near-infrared bands and we made a comparison with the high energy emission. We obtained optical/NIR light curves from Rapid Eye Mounting photometry plus archival Small and Moderate Aperture Research Telescope System data and we accessed the Fermi light curves for the γ-ray data. The periodograms often show strong peaks in the optical and γ-ray bands, which in some cases may be inter-related. The significance of the revealed peaks is then discussed, taking into account that the noise is frequency dependent. Quasi-periodicities on a year-like timescale appear to occur often in blazars. No straightforward model describing these possible periodicities is yet available, but some plausible interpretations for the physical mechanisms causing periodic variabilities of these sources are examined.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Is the pale blue dot unique? Optimized photometric bands for identifying earth-like exoplanets

The next generation of ground- and space-based telescopes will image habitable planets around nearby stars. A growing literature describes how to characterize such planets with spectroscopy, but less consideration has been given to the usefulness of planet colors. Here, we investigate whether potentially Earth-like exoplanets could be identified using UV-visible-to-NIR wavelength broadband photometry (350–1000 nm). Specifically, we calculate optimal photometric bins for identifying an exo-Earth and distinguishing it from uninhabitable planets including both Solar System objects and model exoplanets. The color of some hypothetical exoplanets—particularly icy terrestrial worlds with thick atmospheres—is similar to Earth's because of Rayleigh scattering in the blue region of the spectrum. Nevertheless, subtle features in Earth's reflectance spectrum appear to be unique. In particular, Earth's reflectance spectrum has a “U-shape” unlike all our hypothetical, uninhabitable planets. This shape is partly biogenic because O{sub 2}-rich, oxidizing air is transparent to sunlight, allowing prominent Rayleigh scattering, while ozone absorbs visible light, creating the bottom of the “U.” Whether such uniqueness has practical utility depends on observational noise. If observations are photon limited or dominated by astrophysical sources (zodiacal light or imperfect starlight suppression), then the use of broadband visible wavelength photometry to identify Earth twins has little practical advantage over obtaining detailed spectra. However, if observations are dominated by dark current, then optimized photometry could greatly assist preliminary characterization. We also calculate the optimal photometric bins for identifying extrasolar Archean Earths, and find that the Archean Earth is more difficult to unambiguously identify than a modern Earth twin.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

RESOLVED CO GAS INTERIOR TO THE DUST RINGS OF THE HD 141569 DISK

The disk around HD 141569 is one of a handful of systems whose weak infrared emission is consistent with a debris disk, but still has a significant reservoir of gas. Here we report spatially resolved millimeter observations of the CO(3-2) and CO(1-0) emission as seen with the Submillimeter Array and CARMA. We find that the excitation temperature for CO is lower than expected from cospatial blackbody grains, similar to previous observations of analogous systems, and derive a gas mass that lies between that of gas-rich primordial disks and gas-poor debris disks. The data also indicate a large inner hole in the CO gas distribution and an outer radius that lies interior to the outer scattered light rings. This spatial distribution, with the dust rings just outside the gaseous disk, is consistent with the expected interactions between gas and dust in an optically thin disk. This indicates that gas can have a significant effect on the location of the dust within debris disks.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

INFRARED HIGH-RESOLUTION INTEGRATED LIGHT SPECTRAL ANALYSES OF M31 GLOBULAR CLUSTERS FROM APOGEE

Chemical abundances are presented for 25 M31 globular clusters (GCs), based on moderately high resolution ( R = 22,500) H -band integrated light (IL) spectra from the Apache Point Observatory Galactic Evolution Experiment (APOGEE). Infrared (IR) spectra offer lines from new elements, lines of different strengths, and lines at higher excitation potentials compared to the optical. Integrated abundances of C, N, and O are derived from CO, CN, and OH molecular features, while Fe, Na, Mg, Al, Si, K, Ca, and Ti abundances are derived from atomic features. These abundances are compared to previous results from the optical, demonstrating the validity and value of IR IL analyses. The CNO abundances are consistent with typical tip of the red giant branch stellar abundances but are systematically offset from optical Lick index abundances. With a few exceptions, the other abundances agree between the optical and the IR within the 1 σ uncertainties. The first integrated K abundances are also presented and demonstrate that K tracks the α elements. The combination of IR and optical abundances allows better determinations of GC properties and enables probes of the multiple populations in extragalactic GCs. In particular, the integrated effects of the Na/O anticorrelation can be directly examined for the first time.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

COMPARISON OF DIVERSITY OF TYPE IIB SUPERNOVAE WITH ASYMMETRY IN CASSIOPEIA A USING LIGHT ECHOES

We compare the diversity of spectral line velocities in a large sample of type IIb supernovae (SNe IIb) with the expected asphericity in the explosion, as measured from the light echoes (LEs) of Cassiopeia A (Cas A), which was a historical galactic SN IIb. We revisit the results of Rest et al., who used LEs to observe Cas A from multiple lines of sight and hence determine its asphericity, as seen in the velocity of three spectral lines (He i λ 5876, H α , and the Ca ii near-infrared (NIR) triplet). We confirm and improve on this measurement by reproducing the effect of the LEs in the spectra of several extragalactic SNe IIb found in the literature as well as mean SN IIb spectra recently created by Liu et al. and comparing these to the observed light echo spectra of Cas A, including their associated uncertainties. In order to quantify the accuracy of this comparison, we smooth the light echo spectra of Cas A using Gaussian processes and use a Monte Carlo method to measure the absorption velocities of these three features in the spectra. We then test the hypothesis that the diversity of ejecta velocities seen in SNe IIb can be explained by asphericity. We do this by comparing the range of velocities seen in the different LEs, and hence different lines of sight, of Cas A to that seen in the population of SNe IIb. We conclude that these two ranges are of the same order and thus asphericity could be enough to explain the diversity in the expansion velocity alone.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

EBL Inhomogeneity and Hard-Spectrum Gamma-Ray Sources

The unexpectedly hard very-high-energy (VHE; E > 100 GeV) γ -ray spectra of a few distant blazars have been interpreted as evidence of a reduction of the γγ opacity of the universe due to the interaction of VHE γ -rays with the extragalactic background light (EBL) compared to the expectation from current knowledge of the density and cosmological evolution of the EBL. One of the suggested solutions to this problem involves the inhomogeneity of the EBL. In this paper, we study the effects of such inhomogeneity on the energy density of the EBL (which then also becomes anisotropic) and the resulting γγ opacity. Specifically, we investigate the effects of cosmic voids along the line of sight to a distant blazar. We find that the effect of such voids on the γγ opacity, for any realistic void size, is only of the order of ≲1% and much smaller than expected from a simple linear scaling of the γγ opacity with the line-of-sight galaxy underdensity due to a cosmic void.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Chandra Phase-resolved Spectroscopy of the High Magnetic Field Pulsar B1509−58

We report on a timing and spectral analysis of the young, high magnetic field rotation-powered pulsar (RPP) B1509−58 using Chandra continuous-clocking mode observation. The pulsar’s X-ray light curve can be fit by the two Gaussian components and the pulsed fraction shows moderate energy dependence over the Chandra band. The pulsed X-ray spectrum is well described by a power law with a photon index 1.16(4), which is harder than the values measured with RXTE /PCA and NuSTAR . This result supports the log-parabolic model for the broadband X-ray spectrum. With the unprecedented angular resolution of Chandra , we clearly identified off-pulse X-ray emission from the pulsar, and its spectrum is best fit by a power law plus blackbody model. The latter component has a temperature of ∼0.14 keV with a bolometric luminosity comparable to the luminosities of other young and high magnetic field RPPs, and it lies between the temperature of magnetars and typical RPPs. In addition, we found that the nonthermal X-ray emission of PSR B1509−58 is significantly softer in the off-pulse phase than in the pulsed phase, with the photon index varying between 1.0 and 1.8 and anticorrelated with the flux. This is similar to the behavior of three other young pulsars. We interpreted it as different contributions of pair-creation processes at different altitudes from the neutron star surface according to the outer-gap model.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Double-coronal X-Ray and Microwave Sources Associated with a Magnetic Breakout Solar Eruption

Double-coronal hard X-ray (HXR) sources are believed to be critical observational evidence of bi-directional energy release through magnetic reconnection in large-scale current sheets in solar flares. Here, we present a study on double-coronal sources observed in both HXR and microwave regimes, revealing new characteristics distinct from earlier reports. This event is associated with a footpoint-occulted X1.3-class flare (2014 April 25, starting at 00:17 UT) and a coronal mass ejection that were likely triggered by the magnetic breakout process, with the lower source extending upward from the top of the partially occulted flare loops and the upper source co-incident with rapidly squeezing-in side lobes (at a speed of ∼250 km s{sup −1} on both sides). The upper source can be identified at energies as high as 70–100 keV. The X-ray upper source is characterized by flux curves that differ from those of the lower source, a weak energy dependence of projected centroid altitude above 20 keV, a shorter duration, and an HXR photon spectrum slightly harder than those of the lower source. In addition, the microwave emission at 34 GHz also exhibits a similar double-source structure and the microwave spectra at both sources are in line with gyrosynchrotron emission given by non-thermal energetic electrons. These observations, especially the co-incidence of the very-fast squeezing-in motion of side lobes and the upper source, indicate that the upper source is associated with (and possibly caused by) this fast motion of arcades. This sheds new light on the origin of the corona double-source structure observed in both HXRs and microwaves.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Long-term Study of the Light Curve of PKS 1510-089 in GeV Energies

We have analyzed data from the flat-spectrum radio quasar PKS 1510-089 collected over a period of eight years from 2008 August to 2016 December with the Fermi -LAT. We have identified several flares of this highly variable source, studied their temporal and spectral properties in detail, and compared with previous works on flares of PKS 1510-089. Five major flares and a few subflares or substructures have been identified in our study. The fastest variability time is found to be 1.30 ± 0.18 hr between MJD 55852.063 and 55852.188, where we estimate the minimum size of the emission region to be 4.85 × 10{sup 15} cm. In most of the flares, the spectral energy distributions are better fitted with a log-parabolic distribution compared to a simple power law or a power law with exponential cutoffs. This has strong physics implications regarding the nature of the high-energy gamma-ray emission region.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

An XMM-Newton Study of the Mixed-morphology Supernova Remnant G346.6-0.2

We present an X-ray imaging and spectroscopic study of the molecular cloud interacting mixed-morphology supernova remnant G346.6–0.2 using XMM-Newton . The X-ray spectrum of the remnant is well described by a recombining plasma that most likely arises from adiabatic cooling and has subsolar abundances of Mg, Si, and S. Our fits also suggest the presence of either an additional power-law component with a photon index of ∼2 or an additional thermal component with a temperature of ∼2.0 keV. We investigate the possible origin of this component and suggest that it could arise from either the Galactic ridge X-ray emission, an unidentified pulsar wind nebula, or X-ray synchrotron emission from high-energy particles accelerated at the shock. However, deeper, high-resolution observations of this object are needed to shed light on the presence and origin of this feature. Based on its morphology, its Galactic latitude, the density of the surrounding environment, and its association with a dense molecular cloud, G346.6–0.2 most likely arises from a massive progenitor that underwent core collapse.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

A Search for Quasi-periodic Oscillations in the Blazar 1ES 1959+650

We have searched quasi-periodic oscillations (QPOs) in the 15 GHz light curve of the BL Lac object 1ES 1959+650 monitored by the Owens Valley Radio Observatory 40 m telescope during the period from 2008 January to 2016 February, using the Lomb–Scargle Periodogram, power spectral density (PSD), discrete autocorrelation function, and phase dispersion minimization (PDM) techniques. The red noise background has been established via the PSD method, and no QPO can be derived at the 3 σ confidence level accounting for the impact of the red noise variability. We conclude that the light curve of 1ES 1959+650 can be explained by a stochastic red noise process that contributes greatly to the total observed variability amplitude, dominates the power spectrum, causes spurious bumps and wiggles in the autocorrelation function and can result in the variance of the folded light curve decreasing toward lower temporal frequencies when few-cycle, sinusoid-like patterns are present. Moreover, many early supposed periodicity claims for blazar light curves need to be reevaluated assuming red noise.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1979

Discontinuities in Jovian sulphur plasma

The radial distribution of the Jovian sulfur plasma is discussed. Spectra of the ionized sulfur in the Jovian magnetosphere indicate a sharp discontinuity in visible sulfur emission at a radial distance of six Jupiter radii (Io orbit), outside of which emission is greatly reduced and the plasma is observed not to be in corotation with the planet. Possible explanations of this phenomenon include an effect of Io on the electron temperature outside its orbit, leading to the suppression of S II emission by second ionization, and a current system in Jupiter's ionosphere which prevents plasma from diffusing outward and decouples it from the corotation field. This discontinuity also requires reconciliation with Pioneer observations of the radial and pitch-angle diffusion of energetic charged particles.

Mekler, Y.↗
NASA NTRS1981

The diffuse galactic gamma radiation - The Compton contribution and component separation by energy interval and galactic coordinates

The diffuse high-energy galactic gamma radiation to be expected from cosmic ray interactions with matter and photons is considered with particular emphasis on the contribution of Compton radiation from cosmic ray electrons. The intensity, spectrum and spatial distribution of the expected galactic gamma radiation are estimated based on models of the matter, cosmic ray and photon distributions to take into account the contributions of bremsstrahlung, high-energy cosmic-ray nucleon and interstellar matter interactions as well as Compton interactions between cosmic ray electrons and background photons. Results suggest that the Compton gamma ray contribution from cosmic ray electron interactions with galactic visible and infrared photons is substantially larger than previously believed. Analysis of the energy spectra and latitude dependence of the various sources reveals that the Compton radiation, bremsstrahlung and nuclear cosmic ray-matter interaction radiation should be separable, with Compton radiation dominating at energies from 10 to 100 MeV at galactic latitudes greater than several degrees. Results demonstrate the potential of gamma ray observations in studies of galactic structure, cosmic ray electrons and galactic photon density.

Kniffen, D. A.↗
NASA NTRS1986

Spectral evolution of young stellar objects

An evolutionary sequence, from protostars to pre-main-sequence stars, is suggested for the classification of young stellar objects. This sequence is derived by comparing the predictions of the theoretical models of Adams and Shu with the morphological classification scheme of Lada and Wilking. We first define the spectral index in the near- and mid-infrared, n is identical to d log(nu F sub nu)/d log nu, and then interpret the class of sources with negative spectral indices as protostars. The inferred mass infall rates for these objects are generally consistent with the measured gas temperatures of approx. 35 K in Ophiuchus, and of approx. 10 K in Taurus. Fitting the data requires us to adopt cloud rotation rates in Ophiuchus which are typically an order of magnitude greater than in Taurus, and we speculate on the mechanistic origin for this difference. Next, we consider a subclass of T Tauri stars with near- and mid-infrared excesses and positive or zero spectral indices. We find that the objects with the steeper indices can be understood as the post-infall products from the collapse of rotating cloud cores, where the infrared excesses arise from the simple reprocessing of visible stellar photons in optically thick but spatially thin disks. The sources with flatter spectra may require massive accretion disks. Given the existence of protostars and naked star/disk systems, there is a natural interpretation of another subclass of T Tauri stars, those with two peaks in their emergent spectral energy distributions. These are readily explained as intermediate cases in which dust envelopes still surround the stars and disks. Finally, we find that the theory can be extended to explain the spectral energy distribution of FU Orionis, a famous outburst source. Our model suggests that FU Orionis has a disk, but it offers no discrimination between the competing ideas that the outburst took place on the star or in the disk.

Adams, F. C.↗
NASA NTRS1988

Application of imaging spectrometer data to the Kings-Kaweah ophiolite melange

The Kings-Kaweah ophiolite melange in east-central California is thought to be an obducted oceanic fracture zone and provides the rare opportunity to examine in detail the complex nature of this type of terrain. It is anticipated that the distribution and abundance of components in the melange can be used to determine the relative importance of geologic processes responsible for the formation of fracture zone crust. Laboratory reflectance spectra of field samples indicate that the melange components have distinct, diagnostic absorptions at visible to near-infrared wavelengths. The spatial and spectral resolution of AVIRIS is ideally suited for addressing important scientific questions concerning the Kings-Kaweah ophiolite melange and fracture zones in general.

Mustard, John F.↗
NASA NTRS1989

Column atmospheric water vapor retrievals from airborne imaging spectrometer data

High-spatial-resolution column atmospheric water vapor amounts were derived from spectral data collected by the Airborne Visible Infrared Imaging Spectrometer (AVIRIS). The quantitative derivation is made by curve fitting observed spectra with calculated spectra in the 1.14- and 0.94-micron water-vapor band absorption regions with a nonlinear least-squares technique. The precision of the retrieved column water vapor is approximately 5 percent. The derived column water vapor amounts are independent of the absolute surface reflectance. Curve fitting of spectra near 1 micron from areas covered with vegetation indicates that both the amount of atmospheric water vapor and the moisture content of vegetation can be retrieved simultaneously. It should be possible to measure column water vapor over land areas from satellite altitude with the proposed high-resolution imaging spectrometer or even the moderate-resolution imaging spectrometer.

Gao, Bo-Cai↗