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At least 379 records · Page 21

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NASA NTRS1984

Emission FTIR analyses of thin microscopic patches of jet fuel residue deposited on heated metal surface

Deposits laid down in patches on metal strips in a high pressure/high temperature fuel system simulator operated with aerated fuel at varying flow rates were analyzed by emission FTIR in terms of functional groups. Significant differences were found in the spectra and amounts of deposits derived from fuels to which small concentrations of oxygen-, nitrogen-, or sulfur-containing heterocyclics or metal naphthenates were added. The spectra of deposits generated on strips by heating fuels and air in a closed container were very different from those of the flowing fluid deposits. One such closed-container dodecane deposit on silver gave a strong surface-enhanced Raman spectrum.

Lauer, J. L.↗

NASA NTRS2008

Estimation of the Unsteady Aerodynamic Load on Space Shuttle External Tank Protuberances from a Component Wind Tunnel Test

At the wake of the Columbia (STS-107) accident it was decided to remove the Protuberance Aerodynamic Load (PAL) Ramp that was originally intended to protect various protuberances outside of the Space Shuttle External Tank from high buffet load induced by cross-flows at transonic speed. In order to establish the buffet load without the PAL ramp, a wind tunnel test was conducted where segments of the protuberances were instrumented with dynamic pressure transducers; and power-spectra of sectional lift and drag forces at various span-wise locations between two adjacent support brackets were measured under different cross flow angles, Mach number and other conditions. Additionally, frequency-dependent spatial correlations between the sectional forces were also established. The sectional forces were then adjusted by the correlation length to establish span-averaged spectra of normal and lateral forces that can be suitably "added" to various other unsteady forces encountered by the protuberance. This paper describes the methodology used for calculating the correlation-adjusted power spectrum of the buffet load. A second part of the paper describes wind-tunnel results on the difference in the buffet load on the protuberances with and without the PAL ramp. In general when the ramp height is the same as that of the protuberance height, such as that found on the liquid Oxygen part of the tank, the ramp is found to cause significant reduction of the unsteady aerodynamic load. However, on the liquid Hydrogen part of the tank, where the Oxygen feed-line is far larger in diameter than the height of the PAL ramp, little protection is found to be available to all but the Cable Tray.

Panda, J.↗

NASA NTRS2008

Estimation of the Unsteady Aerodynamic Load on Space Shuttle External Tank Protuberances from a Component Wind Tunnel Test

Panda, Jayatana↗

DOE OSTI2023

J1046+4047: an extremely low-metallicity dwarf star-forming galaxy with O32 = 57

ABSTRACT Using the optical spectrum obtained with the Kitt Peak Ohio State Multi-Object Spectrograph mounted on the Apache Point Observatory 3.5 m Telescope and the Sloan Digital Sky Survey spectrum, we study the properties of one of the most metal-poor dwarf star-forming galaxies (SFGs) in the local Universe, J1046+4047. The galaxy, with a redshift z = 0.04874, was selected from the Data Release 16 of the SDSS. Its properties are among the most extreme for SFGs in several ways. The oxygen abundance 12 + log(O/H) = 7.082 ± 0.016 in J1046+4047 is among the lowest ever observed. With an absolute magnitude Mg = −16.51 mag, a low stellar mass M⋆ = 1.8 × 106 M⊙, and a very low mass-to-light ratio M⋆/Lg ∼ 0.0029 (in solar units), J1046+4047 has a very high specific star formation rate sSFR ∼ 430 Gyr−1, indicating very active ongoing star formation. Another striking feature of J1046+4047 is that it possesses a ratio O32 = I([O iii] λ5007)/I([O ii] λ3727) ∼ 57. Using this extremely high O32, we have confirmed and improved the strong-line calibration for the determination of oxygen abundances in the most metal-deficient galaxies, in the range 12 + log(O/H) ≲ 7.65. This improved method is applicable for all galaxies with O32 ≤ 60. We find the H α emission line in J1046+4047 to be enhanced by some non-recombination processes and thus cannot be used for the determination of interstellar extinction.

Izotov, Y. I. (ORCID:0000000214166082)↗

NASA NTRS1972

Mass spectra stimulated by O+ and Ar+ interacting with a surface.

Beams of O(+) and Ar(+) in the energy range from 100 to 300 eV were directed into an aperture in one face of a copper box. The mass spectrum from a similar aperture in an adjacent face was observed with the aid of a commercial RF quadrupole spectrometer. On the basis of the results obtained it is reported that O(+) beams at about 200 eV may be essentially lost after a few collisions with a surface, in agreement with similar conclusions about atomic oxygen at thermal energies.

Siegel, M. W.↗

NASA NTRS1993

Boundary conditions for the paleoenvironment: Chemical and physical processes in the pre-solar nebula

In observations with the NRAO 12m telescope at Kitt Peak, Arizona, Irvine, a new interstellar radical, CH2N, has been detected. This identification is important for the study of hydrogenation processes in the interstellar medium. In particular, although the abundance of hydrogen is some four orders of magnitude higher than that of other reactive elements in this environment, many organic molecules in quiescent clouds are very unsaturated. This is a consequence of activation barriers which cannot be overcome at the temperatures of cold clouds, even when such reactions are energetically allowed. The hydrogenation series based on the cyanide radical (HnCN) has had four members previously detected in the interstellar medium: CN (n equals O), HCN (n equals l), CH2CN (n equals 3), and CH3NH2 (n equals 5). The recent determination of the rotational spectrum of the CH2N radical through microwave spectroscopy in Japan has made possible a search for this species. In addition to its potential importance for interstellar chemistry, the CH2N radical has been proposed as a reaction intermediate for HCN production in the atmosphere of Jupiter, and as a possible species in the expanding envelopes of oxygen--rich evolved stars. We detected CH2N in the cold cloud TMC--1 where the abundance seems to be some three orders of magnitude lower than that of HCN. A tentative detection was made in the Galactic Center molecular cloud Sgr B2. To our knowledge, there are no predicted abundances of CH2N from models of interstellar chemistry.

Irvine, William M.↗

NASA NTRS1989

Theoretical studies of the infrared emission from circumstellar dust shells: the infrared characteristics of circumstellar silicates and the mass-loss rate of oxygen-rich late-type giants

We have modeled the infrared emission of spherically symmetric, circumstellar dust shells with the aim of deriving the infrared absorption properties of circumstellar silicate grains and the mass-loss rates of the central stars. As a basis for our numerical studies, a simple semianalytical formula has been derived that illustrates the essential characteristics of the infrared emission of such dust shells. A numerical radiative transfer program has been developed and applied to dust shells around oxygen-rich late-type giants. Free parameters in such models include the absorption properties and density distribution of the dust. An approximate, analytical expression is derived for the density distribution of circumstellar dust driven outward by radiation pressure from a central source. A large grid of models has been calculated to study the influence of the free parameters on the emergent spectrum. These results form the basis for a comparison with near-infrared observations. Observational studies have revealed a correlation between the near-infrared color temperature, Tc, and the strength of the 10 micrometers emission or absorption feature, A10. This relationship, which essentially measures the near-infrared optical depth in terms of the 10 micrometers optical depth, is discussed. Theoretical A10-Tc relations have been calculated and compared to the observations. The results show that this relation is a sensitive way to determine the ratio of the near-infrared to 10 micrometers absorption efficiency of circumstellar silicates. These results as well as previous studies show that the near-infrared absorption efficiency of circumstellar silicate grains is much higher than expected from terrestrial minerals. We suggest that this enhanced absorption is due to the presence of ferrous iron (Fe2+) color centers dissolved in the circumstellar silicates. By using the derived value for the ratio of the near-infrared to 10 micrometers absorption efficiency, the observed A10-Tc relation can be calibrated in terms of the total dust column density of the circumstellar shell and thus the mass-loss rate of late-type giants can easily be derived. Detailed models have been made of the infrared emission of three well-studied Miras: R Cas, IRC 10011, and OH 26.5+0.6, with the emphasis on the shape of the 10 micrometers emission or absorption feature. The results show that the intrinsic shape of the 10 micrometers resonance varies from a very broad feature in R Cas to a relatively narrower feature in OH 26.5+0.6, with IRC 10011 somewhere in between. Possible origins of this variation are discussed. The mass-loss rates from these objects are calculated to be 3 x 10(-7), 2 x 10(-5), and 2 x 10(-4) M Sun yr-1 for R Cas, IRC 10011, and OH 26.5+0.6, respectively. These results are compared to other determinations in the literature.

NASA Discipline Exobiology↗

NASA NTRS1989

Plasma density fluctuations observed during Space Shuttle Orbiter water releases

Observations by the Langmuir probe on the Plasma Diagnostics Package flown as part of the Spacelab 2 mission in the summer of 1985 show a strong increase in the level of turbulence near the Shuttle Orbiter during operations in which liquid water is released. The spectrum of the plasma density fluctuations peaks at the lowest frequencies measured (a few Hz) and extends up to a few kHz, near the lower hybrid frequency. Two potential mechanisms for generating the plasma turbulence are suggested which are both based on the production of water ions as a result of charge exchange with the ambient oxygen ions in the ionosphere. The first mechanism proposed is the ion-plasma instability which arises from the drift of the contaminant with respect to the ambient oxygen ions. The other mechanism proposed is the Ott-Farley instability, which is a result of the ring distribution formed by the 'pick-up' water ions.

Pickett, J. S.↗

NASA NTRS1993

Backscatter Mossbauer Spectrometer (BaMS) for extraterrestrial applications

Mossbauer spectroscopy is a nuclear gamma resonance technique particularly well suited to the study of materials that contain iron (Fe-57). It can provide information on the oxidation state of iron as well as the type and proportion of iron-containing mineral species in a sample of interest. Iron Mossbauer spectroscopy (FeMS) has been applied to samples believed to have come from Mars (SNC meteorites) and has been helpful in refining the choice among putative Martian surface materials by suggesting a likely nanophase component of the Martian regolity. FeMS spectrum of a Martial analogue material (Hawaiian palagonite) is shown; it is dominated by ferric-bearing phases and shows evidence of a nanophase component. FeMS has also been applied to lunar materials. It can be used to measure the maturity of lunar surface material and has been proposed as a prospector for lunar ilmenite, an oxygen resource mineral. Several years ago we suggested a backscatter Mossbauer spectrometer (BaMS) for a Mars rover mission. Backscatter design was selected as most appropriate for in-situ application because no sample preparation is required. Since that time, we have continued to develop the BaMS instrument in anticipation that it would eventually find a home on a NASA planetary mission. Gooding proposed BaMS as a geochemistry instrument on MESUR. More recently, an LPI workshop has recommended that BaMS be included in a three-instrument payload on the next (1996?) lunar lander.

Agresti, D. G.↗

NASA NTRS2017

Airborne Demonstration of Atmospheric Oxygen Optical Depth Measurements with an Integrated Path Differential Absorption Lidar

We report on an airborne demonstration of atmospheric oxygen (O2) optical depth measurements with an Integrated Path Differential Absorption (IPDA) lidar using a fiber-based laser transmitter and photon counting detectors. Accurate atmospheric temperature and pressure measurements are needed for NASA's Active Sensing of CO2 Emissions over Nights, Days and Seasons (ASCENDS) mission. Since O2 is uniformly mixed in the atmosphere, its spectrum can be used to estimate the dry mixing ratio of CO2. In its airborne configuration, the IPDA lidar uses an Erbium Doped Fiber amplifier, a frequency doubler and single photon counting detectors to measure O2 absorption at multiple wavelengths near 765 nm. This instrument was deployed in 2013 and 2014 aboard NASA's DC-8 airborne laboratory as part of two campaigns to measure CO2 mixing ratios over a wide range of topography and weather conditions from altitudes ranging between 3 km and 13 km. In this paper we will review a summary of the results from our flights, discuss the errors that limit the precision and accuracy of the measurement and identify possible areas of improvement.

Methane↗

NASA NTRS1991

First results from the Goddard High-Resolution Spectrograph - Spectroscopic determination of stellar parameters of Melnick 42, an O3f star in the Large Magellanic Cloud

GHRS and optical (ESO 3.6 m) observations of the O3f star Melnick 42 in the 30 Doradus complex are reported. A first analysis reveals that with a luminosity of 2.3 million L(solar) and a present mass of 100 M(solar), Melnick 42 is one of the most luminous and massive stars known. An estimate of abundances indicates that iron and oxygen are very likely reduced by a factor of four relative to the sun, whereas carbon is more strongly depleted and nitrogen is approximately solar. The terminal velocity of the stellar wind is 3000 km/s. The mass-loss rate is 4 x 10 to the -6th M(solar)/yr, with a large uncertainty. The excellent quality GHRS spectrum taken in a crowded region of the LMC demonstrates the superiority of the HST for quantitative ultraviolet spectroscopy of hot stars in other galaxies.

Heap, S. R.↗

DOE OSTI2021

The Coronal Line Spectrum of the Iron Nova V3666 Ophiuchi

Optical and infrared spectroscopy are presented for the classical nova V3666 Ophiuchi (Nova Ophiuchi 2018 No.3) from 11 months after its outburst. At that epoch, V3666 Oph displayed an [Fe x] λ0.6375 emission line stronger than Hα and nearly a factor of 3 larger, relative to Hα, than in any nova observed previously. The [Fe x] feature, with an equivalent width exceeding 1300 Å, was enormously strong relative to the continuum emission as well. V3666 Oph also reached a state of high excitation for an Fe ii type nova, displaying coronal lines of [Fe xi], [S ix], and [Ar x], and permitted features that can be identified with the C vi (8–7), (9–8), and (10–9) transitions. In addition to [Fe x] and [Fe xi], V3666 Oph also displayed bright lines of [Fe vii], indicating that the prominent iron features were not confined to a single or narrow range of ionization states. Modeling the emission line spectrum of V3666 Oph with the photoionization code Cloudy indicated that the bulk of the emission line gas was matter-bounded, severely reducing the amount of low ionization gas and resulting in coronal lines that were very strong in comparison to lines such as H i and He i, and the familiar low excitation forbidden lines of nitrogen and oxygen. Such matter-bounded regions are observationally rare in novae since they are both faint and short-lived, offering a plausible explanation for why [Fe x] λ0.6375 had not be seen at this strength previously.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2024

Nonlinear light-output calibration of the oxygenated xylene scintillators used in OMEGA neutron time-of-flight spectrometers

Neutron time-of-flight (nTOF) spectrometers are essential instruments for measuring and evaluating the performance of inertial confinement fusion implosions. The neutron spectrometers utilized for the OMEGA laser include two liquid-based scintillators, each consisting of a large volume filled with xylene that is coupled to four photomultiplier tubes. Analysis of the signal from these detectors requires detailed knowledge of the scintillator’s light output, which is needed to fit the nTOF spectrum, from which the neutron energy spectrum is informed. The light output is nonlinearly proportional to the neutron energy, which, in turn, affects the interpretation of the neutron energy spectrum from a TOF signal. A recent campaign on OMEGA was performed to calibrate the xylene detectors and infer the shape of the light-output curve. The campaign utilized materials with increasing Z placed in the OMEGA target chamber to initiate scattering events with the 14 MeV fusion neutrons. This process leads to the production of backscatter neutrons of varying energies that appear as peaks in the nTOF data. Simulations using a neutron transport code were combined with the measured deuterium–tritium neutron yields to calculate the expected backscattered neutron yields from the well-known scattering cross sections of each material. Furthermore, the neutron-energy dependent light output of the scintillator inferred from the experiment is compared to the light-output curve simulated with a neutron transport code for the following neutron energies: 1.5, 2.5, 6, and 14 MeV.

47 OTHER INSTRUMENTATION↗

NASA NTRS1982

Analysis of nitrogen and oxygen far ultraviolet auroral emissions

Far ultraviolet observations of the auroral and airglow provide quantitative diagnostics of atmospheric abundances, energy deposition, and excitation processes because many atmospheric species have resonance transitions in this spectral region. The spectroscopy of an active auroral arc observed above Fort Churchill on March 29, 1978, has been discussed by Feldman and Gentieu (1982). The present investigation attempts to quantify the measurements with the aid of a self-consistent approach used by Meier et al. (1980). It is shown that the primary electron spectrum has a characteristic energy of 1.75-2.5 keV, corresponding to energy deposition rates of 5-8 erg/(sq cm-sec). Atomic nitrogen emissions resulting from molecular dissociative excitation show no evidence of multiple scattering, in contrast to data from other auroras.

Meier, R. R.↗

NASA NTRS2007

Suzaku Observation of Diffuse X-ray Emission from the Carina Nebula

We studied extended X-ray emission from the Carina Nebula taken with the Suzaku CCD camera XIS on 2005 Aug. 29. The X-ray morphology, plasma temperature and absorption to the plasma are consistent with the earlier Einstein results. The Suzaku spectra newly revealed emission lines from various spices including oxygen, but not from nitrogen. This result restricts the N/O ratio significantly low, compared with evolved massive stellar winds, suggesting that the diffuse emission is originated in an old supernova remnant or a super shell produced by multiple supernova remnants. The X-ray spectra from the north and south of eta Car showed distinct differences between 0.3-2 keV. The south spectrum shows strong L-shell lines of iron ions and K-shell lines of silicon ions, while the north spectrum shows them weak in intensity. This means that silicon and iron abundances are a factor of 2-4 higher in the south region than in the north region. The abundance variation may be produced by an SNR ejecta, or relate to the dust formation around the star forming core.

Hamaguchi, Kenji↗

NASA NTRS1990

Experimental investigations of low-energy (4 to 40 eV) collisions of O(-)(P2) ions and O(P3) atoms with surfaces

Using a newly-developed, magnetically confined source, low-energy, ground state oxygen negative ions and neutral atoms are generated. The energy range is variable, and atom and neutrals have been generated at energies varying from 2 eV to 40 eV and higher. It was found that the interaction of these low-energy species with a solid magnesium fluoride target leads to optical emissions in the (at least) visible and infrared regions of the spectrum. Researchers describe y details of the photodetachment source, and present spectra of the neutral and ion glows in the wavelength range 250 to 850 nm (for O(-)) and 600 to 850 nm (for O), and discuss the variability of the emissions for incident energies between 4 and 40 eV.

Chutjian, A.↗

NASA NTRS1990

Experimental investigations of low-energy (4-40 eV) collisions of O-(2P) ions and O(3P) atoms with surfaces

Using a newly-developed, magnetically confined source, low-energy, ground state oxygen negative ions and neutral atoms are generated. The energy range is variable, and atom and neutrals have been generated at energies varying from 2 eV to 40 eV and higher. It was found that the interaction of these low-energy species with a solid magnesium fluoride target leads to optical emissions in the (at least) visible and infrared regions of the spectrum. Researchers describe y details of the photodetachment source, and present spectra of the neutral and ion glows in the wavelength range 250 to 850 nm (for O/-/) and 600 to 850 nm (for O), and discuss the variability of the emissions for incident energies between 4 and 40 eV.

Orient, O. J.↗

NASA NTRS1973

X-ray spectrum of Cassiopeia A - Evidence for iron line emission.

A sensitive measurement by rocket-borne detectors of the X-ray flux from Cas A has revealed a steep continuum and a broad spectral feature in the region where line radiation from iron nuclei would be expected. The flux in this feature is 0.0122 plus or minus 0.0017 photons per sq cm per sec. The presence of broad iron lines is consistent with a model in which about 13 MeV-per-nucleon iron nuclei charge exchange with surrounding interstellar oxygen and other heavy atoms. The model suggests that a substantial fraction of the energy from the outburst has gone into low-energy cosmic rays which produce the observed H II region surrounding the remnant.

Serlemitsos, P. J.↗