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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.

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At least 1,387 records · Page 77
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

FT-IR spectroscopic studies of polycyclic aromatic hydrocarbons

Proper assessment of the hypothesis which correlates polycyclic aromatic hydrocarbons (PAHs) with the unidentified infrared emission bands requires additional experimental laboratory data. In order to address this need, thermal infrared emission studies were performed on a subset of PAHs suggested to be of astrophysical importance. It was proposed that infrared emission from interstellar PAHs occurs following absorption of an ultraviolet photon. Since energy transfer to the ground electronic state can be rapid for a species in which intersystem crossing is negligible, the emission spectrum may be viewed as resulting from an equilibrium vibrational temperature (Leger and d'Hendecourt, 1987). This has been the basis for using infrared absorption spectra to calculate the corresponding emission spectra at various temperatures. These calculations were made using room temperature infrared absorption coefficients instead of those at the temperature of interest because of the latter's unavailability. The present studies are designed to address the differences between the calculated and experimental thermal emission spectra and to provide information which will be useful in future ultraviolet induced infrared fluorescence studies. The emission spectra have been obtained for temperatures up to 825K using an emission cell designed to mount against an external port of an FT-IR spectrometer. These spectra provide information concerning relative band intensities and peak positions which is unavailable from previous calculations.

Salisbury, D. W.↗
DOE OSTI2015

DETECTION OF BROAD Hα EMISSION LINES IN THE LATE-TIME SPECTRA OF A HYDROGEN-POOR SUPERLUMINOUS SUPERNOVA

iPTF13ehe is a hydrogen-poor superluminous supernova (SLSN) at z = 0.3434, with a slow-evolving light curve and spectral features similar to SN2007bi. It rises in 83–148 days to reach a peak bolometric luminosity of ∼1.3 × 10{sup 44} erg s{sup −1}, then decays slowly at 0.015 mag day{sup −1}. The measured ejecta velocity is ∼ 13,000 km s{sup −1}. The inferred explosion characteristics, such as the ejecta mass (70–220 M{sub ⊙}), and the total radiative and kinetic energy (E{sub rad} ∼ 10{sup 51} erg, E{sub kin} ∼ 2 × 10{sup 53} erg), are typical of slow-evolving H-poor SLSN events. However, the late-time spectrum taken at +251 days (rest, post-peak) reveals a Balmer Hα emission feature with broad and narrow components, which has never been detected before among other H-poor SLSNe. The broad component has a velocity width of ∼4500 km s{sup −1} and a ∼300 km s{sup −1} blueward shift relative to the narrow component. We interpret this broad Hα emission with a luminosity of ∼2 × 10{sup 41} erg s{sup −1} as resulting from the interaction between the supernova ejecta and a discrete H-rich shell, located at a distance of ∼4 × 10{sup 16} cm from the explosion site. This interaction causes the rest-frame r-band LC to brighten at late times. The fact that the late-time spectra are not completely absorbed by the shock-ionized H-shell implies that its Thomson scattering optical depth is likely ≤1, thus setting upper limits on the shell mass ≤30 M{sub ⊙}. Of the existing models, a Pulsational Pair Instability supernova model can naturally explain the observed 30 M{sub ⊙} H-shell, ejected from a progenitor star with an initial mass of (95–150) M{sub ⊙} about 40 years ago. We estimate that at least ∼15% of all SLSNe-I may have late-time Balmer emission lines.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

LINE PARAMETERS OF THE 782 nm BAND OF CO{sub 2}

The 782 nm band of CO{sub 2}, in a transparent window of Earth's atmosphere, was the first CO{sub 2} band observed 80 yr ago in the spectra of Venus. The band is very weak and therefore not saturated by the thick atmosphere of Venus, but its spectral parameters are still very limited due to the difficulty of detecting it in the laboratory. It is the highest overtone (ν{sub 1} + 5ν{sub 3}) of CO{sub 2} given in widely used spectroscopy databases such as HITRAN and GEISA. In the present work, the band is studied using a cavity ring-down spectrometer with ultra-high sensitivity as well as high precision. The positions of 55 lines in the band were determined with an absolute accuracy of 3 × 10{sup –5} cm{sup –1}, two orders of magnitude better than previous studies. The line intensities, self-induced pressure broadening coefficients, and the shift coefficients were also derived from the recorded spectra. The obtained spectral parameters can be applied to model the spectra of the CO{sub 2}-rich atmospheres of planets like Venus and Mars.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

The water abundance of the directly imaged substellar companion κ and b retrieved from a near infrared spectrum

Spectral retrieval has proven to be a powerful tool for constraining the physical properties and atmospheric compositions of extrasolar planet atmospheres based on observed spectra, primarily for transiting objects but also for directly imaged planets and brown dwarfs. Despite its strengths, this approach has been applied to only about a dozen targets. Determining the abundances of the main carbon- and oxygen-bearing compounds in a planetary atmosphere can lead to the C/O ratio of the object, which is crucial for understanding its formation and migration history. We present a retrieval analysis of the published near-infrared spectrum of κ Andromedae b, a directly imaged substellar companion to a young B9 star. We fit the emission spectrum model utilizing a Markov Chain Monte Carlo algorithm. We estimate the abundance of water vapor, and its uncertainty, in the atmosphere of the object. In addition, we place an upper limit on the abundance of CH{sub 4}. We qualitatively compare our results with studies that have applied model retrieval on multiband photometry and emission spectroscopy of hot Jupiters (extrasolar giant planets with orbital periods of several days) and the directly imaged giant planet HR 8799b.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

X-RAY PHASE-RESOLVED SPECTROSCOPY OF PSRs B0531+21, B1509-58, AND B0540-69 WITH RXTE

The Rossi X-Ray Timing Explorer (RXTE) has made hundreds of observations on three famous young pulsars (PSRs) B0531+21 (Crab), B1509-58, and B0540-69. Using the archive RXTE data, we have studied the phase-resolved spectral properties of these pulsars in details. The variation of the X-ray spectrum with phase of PSR B0531+21 is confirmed here much more precisely and more details are revealed than in the previous studies: The spectrum softens from the beginning of the first pulse, turns to harden right at the pulse peak and becomes the hardest at the bottom of the bridge, softens gradually until the second peak, and then softens rapidly. Different from the previous studies, we found that the spectrum of PSR B1509-58 is significantly harder in the center of the pulse, which is also in contrast to that of PSR B0531+21. The variation of the X-ray spectrum of PSR B0540-69 seems similar to that of PSR B1509-58, but with a lower significance. Using about 10 years of data span, we also studied the real time evolution of the spectra of these pulsars, and no significant evolution has been detected. We discuss the constraints of these results on theoretical models of pulsar X-ray emission.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Neutron-induced defects in optical fibers

We present a study on 0.8 MeV neutron-induced defects up to fluences of 10{sup 17} n/cm{sup 2} in fluorine doped optical fibers by using electron paramagnetic resonance, optical absorption and confocal micro-luminescence techniques. Our results allow to address the microscopic mechanisms leading to the generation of Silica-related point-defects such as E', H(I), POR and NBOH Centers.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Optical properties and structure of beryllium lead silicate glasses

Luminescence and optical properties and structural features of (BeO){sub x}(PbO⋅SiO{sub 2}){sub 1−x} glasses (x = 0 ÷ 0.3) are investigated by means of optical absorption and photoluminescence spectroscopy and X-ray diffraction. The regularities of the formation of the optical absorption edge and static disorder are studied. It is shown that the optical absorption and luminescence are determined by transitions between localized states of lead ions. The impact of beryllium oxide on optical and luminescence properties and electronic structure of bands tails is discussed. The presence of two different concentration ranges with various short-range order structure and band tails nature has been established.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

RED SUPERGIANT STARS AS COSMIC ABUNDANCE PROBES. II. NLTE EFFECTS IN J-BAND SILICON LINES

Medium-resolution J-band spectroscopy of individual red supergiant stars is a promising tool to investigate the chemical composition of the young stellar population in star-forming galaxies. As a continuation of recent work on iron and titanium, detailed non-LTE (NLTE) calculations are presented to investigate the influence of NLTE on the formation of silicon lines in the J-band spectra of red supergiants. Substantial effects are found resulting in significantly stronger absorption lines of neutral silicon in NLTE. As a consequence, silicon abundances determined in NLTE are significantly smaller than in local thermodynamic equilibrium (LTE) with the NLTE abundance corrections varying smoothly between -0.4 dex and -0.1 dex for effective temperatures between 3400 K and 4400 K. The effects are largest at low metallicity. The physical reasons behind the NLTE effects and the consequences for extragalactic J-band abundance studies are discussed.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

A combined Spitzer and Herschel infrared study of gas and dust in the circumbinary disk orbiting V4046 Sgr

We present results from a spectroscopic Spitzer and Herschel mid-to-far-infrared study of the circumbinary disk orbiting the evolved (age ∼12–23 Myr) close binary T Tauri system V4046 Sgr. Spitzer InfraRed Spectrograph spectra show emission lines of [Ne ii], H{sub 2} S(1), CO{sub 2}, and HCN, while Herschel Photodetector Array Camera and Spectrometer and Spectral and Photometric Imaging Receiver spectra reveal emission from [O i], OH, and tentative detections of H{sub 2}O and high-J transitions of CO. We measure [Ne iii]/[Ne ii] ≲ 0.13, which is comparable to other X-ray/EUV luminous T Tauri stars that lack jets. We use the H{sub 2} S(1) line luminosity to estimate the gas mass in the relatively warm surface layers of the inner disk. The presence of [O i] emission suggests that CO, H{sub 2}O, and/or OH is being photodissociated, and the lack of [C i] emission suggests any excess C may be locked up in HCN, CN, and other organic molecules. Modeling of silicate dust grain emission features in the mid-infrared indicates that the inner disk is composed mainly of large (r ∼ 5 μm) amorphous pyroxene and olivine grains (∼86% by mass) with a relatively large proportion of crystalline silicates. These results are consistent with other lines of evidence indicating that planet building is ongoing in regions of the disk within ∼30 AU of the central, close binary.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Large-scale uniform ZnO tetrapods on catalyst free glass substrate by thermal evaporation method

Highlights: • Investigate the growth of ZnO-Ts on glass substrate by thermal evaporation method. • Glass substrate without any catalyst or a seed layer. • The morphology was controlled by adjusting the temperature of the material and the substrate. • Glass substrate was placed vertically in the quartz tube. - Abstract: Here, we report for the first time the catalyst-free growth of large-scale uniform shape and size ZnO tetrapods on a glass substrate via thermal evaporation method. Three-dimensional networks of ZnO tetrapods have needle–wire junctions, an average leg length of 2.1–2.6 μm, and a diameter of 35–240 nm. The morphology and structure of ZnO tetrapods were investigated by controlling the preparation temperature of each of the Zn powder and the glass substrate under O{sub 2} and Ar gases. Studies were carried out on ZnO tetrapods using X-ray diffraction, field emission scanning electron microscopy, UV–vis spectrophotometer, and a photoluminescence. The results showed that the sample grow in the hexagonal wurtzite structure with preferentially oriented along (002) direction, good crystallinity and high transmittance. The band gap value is about 3.27 eV. Photoluminescence spectrum exhibits a very sharp peak at 378 nm and a weak broad green emission.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Synthesis and photoluminescence properties of ALa{sub 9}(SiO{sub 4}){sub 6}O{sub 2}: Eu{sup 3+} (A = Li, Na) red phosphor

Highlights: • The ALa{sub 9}(SiO{sub 4}){sub 6}O{sub 2}: Eu{sup 3+} (A = Li, Na) red phosphors were synthesized. • Photoluminescence (PL) properties of ALa{sub 9}(SiO{sub 4}){sub 6}O{sub 2}: Eu{sup 3+} (A = Li, Na) phosphors also were discussed. • ALa{sub 9}(SiO{sub 4}){sub 6}O{sub 2}: Eu{sup 3+} (A = Li, Na) could be a potential red phosphor for NUV LEDs and displays. - Abstract: ALa{sub 9}(SiO{sub 4}){sub 6}O{sub 2}: Eu{sup 3+} (A = Li, Na) oxyapatite phosphors have been synthesized via traditional solid-state methods X-ray powder diffraction (XRD) analysis confirmed the phase formation of ALa{sub 9}(SiO{sub 4}){sub 6}O{sub 2}: Eu{sup 3+} (A = Li, Na) materials. The scanning electron microscope (SEM) image exhibited the irregular morphology of ALa{sub 9}(SiO{sub 4}){sub 6}O{sub 2}: Eu{sup 3+} (A = Li, Na) particles. The photoluminescence excitation (PLE) and emission (PL) spectra were investigated. The results showed that the phosphor could be efficiently excited by the near ultraviolet (NUV) light, and it exhibited red light emission. The calculated color coordinates lies in the red region. All the obtained results suggest that the prepared phosphors exhibit great potential application as red emitting phosphor for near ultraviolet white light emitting diodes (NUV WLEDs).

36 MATERIALS SCIENCE↗
DOE OSTI2015

Infrared laser induced population transfer and parity selection in {sup 14}NH{sub 3}: A proof of principle experiment towards detecting parity violation in chiral molecules

We have set up an experiment for the efficient population transfer by a sequential two photon—absorption and stimulated emission—process in a molecular beam to prepare quantum states of well defined parity and their subsequent sensitive detection. This provides a proof of principle for an experiment which would allow for parity selection and measurement of the time evolution of parity in chiral molecules, resulting in a measurement of the parity violating energy difference Δ{sub pv}E between enantiomers of chiral molecules. Here, we present first results on a simple achiral molecule demonstrating efficient population transfer (about 80% on the average for each step) and unperturbed persistence of a selected excited parity level over flight times of about 1.3 ms in the beam. In agreement with model calculations with and without including nuclear hyperfine structure, efficient population transfer can be achieved by a rather simple implementation of the rapid adiabatic passage method of Reuss and coworkers and considering also the stimulated Raman adiabatic passage technique of Bergmann and coworkers as an alternative. The preparation step uses two powerful single mode continuous wave optical parametric oscillators of high frequency stability and accuracy. The detection uses a sensitive resonantly enhanced multiphoton ionization method after free flight lengths of up to 0.8 m in the molecular beam. Using this technique, we were able to also resolve the nuclear hyperfine structure in the rovibrational levels of the ν{sub 1} and ν{sub 3} fundamentals as well as the 2ν{sub 4} overtone of {sup 14}NH{sub 3}, for which no previous data with hyperfine resolution were available. We present our new results on the quadrupole coupling constants for the ν{sub 1}, ν{sub 3}, and 2ν{sub 4} levels in the context of previously known data for ν{sub 2} and its overtone, as well as ν{sub 4}, and the ground state. Thus, now, {sup 14}N quadrupole coupling constants for all fundamentals and some overtones of {sup 14}NH{sub 3} are known and can be used for further theoretical analysis.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

OPTICAL SPECTROSCOPIC SURVEY OF HIGH-LATITUDE WISE-SELECTED SOURCES

We report on the results of an optical spectroscopic survey at high Galactic latitude (|b| {>=} 30 Degree-Sign ) of a sample of WISE-selected targets, grouped by WISE W1 ({lambda}{sub eff} = 3.4 {mu}m) flux, which we use to characterize the sources WISE detected. We observed 762 targets in 10 disjoint fields centered on ultraluminous infrared galaxy candidates using DEIMOS on Keck II. We find 0.30 {+-} 0.02 galaxies arcmin{sup -2} with a median redshift of z = 0.33 {+-} 0.01 for the sample with W1 {>=} 120 {mu}Jy. The foreground stellar densities in our survey range from 0.23 {+-} 0.07 arcmin{sup -2} to 1.1 {+-} 0.1 arcmin{sup -2} for the same sample. We obtained spectra that produced science grade redshifts for {>=}90% of our targets for sources with W1 flux {>=}120 {mu}Jy that also had an i-band flux {approx}> 18 {mu}Jy. We used this for targeting very preliminary data reductions available to the team in 2010 August. Our results therefore present a conservative estimate of what is possible to achieve using WISE's Preliminary Data Release for the study of field galaxies.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

ENHANCED INTERFEROMETRIC IDENTIFICATION OF SPECTRA IN HABITABLE EXTRASOLAR PLANETS

An Earth-like extrasolar planet emits light that is many orders of magnitude fainter than that of the parent star. We propose a method of identifying bio-signature spectral lines in light of known extrasolar planets based on Fourier spectroscopy in the infrared, using an off-center part of a Fourier interferogram only. This results in superior sensitivity to narrower molecular-type spectral bands, which are expected in the planet spectrum but are absent in the parent star. We support this idea by numerical simulations that include photon and thermal noise, and show it to be feasible at a luminosity ratio of 10{sup -6} for a Sun-like parent star in the infrared. We also carried out a laboratory experiment to illustrate the method. The results suggest that this method should be applicable to real planet searches.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

TIME-VARYING POTASSIUM IN HIGH-RESOLUTION SPECTRA OF THE TYPE IA SUPERNOVA 2014J

We present a time series of the highest resolution spectra yet published for the nearby Type Ia supernova (SN Ia) 2014J in M82. They were obtained at 11 epochs over 33 days around peak brightness with the Levy Spectrograph (resolution R ≈ 110,000) on the 2.4 m Automated Planet Finder telescope at Lick Observatory. We identify multiple Na i D and K i absorption features as well as absorption by Ca ii H and K and several of the more common diffuse interstellar bands (DIBs). We see no evolution in any component of Na i D, Ca ii, or in the DIBs, but do establish the dissipation/weakening of the two most blueshifted components of K i. We present several potential physical explanations, finding the most plausible to be photoionization of circumstellar material, and discuss the implications of our results with respect to the progenitor scenario of SN 2014J.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

AN INFRARED DIFFUSE CIRCUMSTELLAR BAND? THE UNUSUAL 1.5272 μm DIB IN THE RED SQUARE NEBULA

The molecular carriers of the ubiquitous absorption features called the diffuse interstellar bands (DIBs) have eluded identification for many decades, in part because of the enormous parameter space spanned by the candidates and the limited set of empirical constraints afforded by observations in the diffuse interstellar medium. Detection of these features in circumstellar regions, where the environmental properties are more easily measured, is thus a promising approach to understanding the chemical nature of the carriers themselves. Here, using high-resolution spectra from the Apache Point Observatory Galactic Evolution Experiment survey, we present an analysis of the unusually asymmetric 1.5272 μm DIB feature along the sightline to the Red Square Nebula (RSN) and demonstrate the likely circumstellar origin of about half of the DIB absorption in this line of sight. This interpretation is supported both by the velocities of the feature components and by the ratio of foreground to total reddening along the line of sight. The RSN sightline offers the unique opportunity to study the behavior of DIB carriers in a constrained environment and thus to shed new light on the carriers themselves.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Calculation of Spectra of Neutrons and Charged Particles Produced in a Target of a Neutron Generator

An algorithm for calculating the spectra of neutrons and associated charged particles produced in the target of a neutron generator is detailed. The products of four nuclear reactions {sup 3}H(d,n){sup 4}He, {sup 2}H(d,n){sup 3}He, {sup 2}H(d,p){sup 3}H, and {sup 3}He(d,p){sup 4}He are analyzed. The results of calculations are presented in the form of neutron spectra for several emission angles and spectra of associated charged particles emitted at an angle of 180° for a deuteron initial energy of 0.13 MeV.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2015

Optical and structural properties of ensembles of colloidal Ag{sub 2}S quantum dots in gelatin

The size dependences of the absorption and luminescence spectra of ensembles of hydrophilic colloidal Ag{sub 2}S quantum dots produced by the sol-gel method and dispersed in gelatin are analyzed. By X-ray diffraction analysis and transmission electron microscopy, the formation of core/shell nanoparticles is detected. The characteristic feature of the nanoparticles is the formation of crystalline cores, 1.5–2.0 nm in dimensions, and shells of gelatin and its complexes with the components of synthesis. The observed slight size dependence of the position of infrared photoluminescence bands (in the range 1000–1400 nm) in the ensembles of hydrophilic colloidal Ag{sub 2}S quantum dots is explained within the context of the model of the radiative recombination of electrons localized at structural and impurity defects with free holes.

36 MATERIALS SCIENCE↗