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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 1,495 records · Page 83
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Signal-to-noise ratios in IUE SWP-LO spectra of chromospheric emission-line sources

The short-wavelength-prime (SWP) detector of the International Ultraviolet Explorer should operate near the photon-counting limit, but the noise levels in flat-field images are several times higher. The exaggerated noise can be traced to the incomplete removal of the pixel-to-pixel granularity of the television frames by the prevailing spectral image processing system. An empirical noise model for the current-epoch photometric linearization strategy and one for a hypothetical processing system that achieves complete flat fielding of the raw images are derived. A formula is then proposed to predict the signal-to-noise ratio in the measured flux of an emission line (possibly superimposed on a smooth continuum) in an IUE low-dispersion (5 A resolution) far-ultraviolet (1150 A-1950 A) spectrum as recorded with the SWP camera. For illustration, the formula is specialized to the important C IV 1549 A feature of F-K stars. The S/N relation permits one to determine sensitivity limits, upper limits in faint exposures, and optimum exposure times.

Ayres, Thomas R.↗
NASA NTRS1995

In situ phytoplankton absorption, fluorescence emission, and particulate backscattering spectra determined from reflectance

An inverse model was developed to extract the absortion and scattering (elastic and inelastic) properties of oceanic constituents from surface spectral reflectance measurements. In particular, phytoplankton spectral absorption coefficients, solar-stimulated chlorophyll a fluorescence spectra, and particle backscattering spectra were modeled. The model was tested on 35 reflectance spectra obtained from irradiance measurements in optically diverse ocean waters (0.07 to 25.35 mg/cu m range in surface chlorophyll a concentrations). The universality of the model was demonstrated by the accurate estimation of the spectral phytoplankton absorption coefficents over a range of 3 orders of magnitude (rho = 0.94 at 500 nm). Under most oceanic conditions (chlorophyll a less than 3 mg/cu m) the percent difference between measured and modeled phytoplankton absorption coefficents was less than 35%. Spectral variations in measured phytoplankton absorption spectra were well predicted by the inverse model. Modeled volume fluorescence was weakly correlated with measured chl a; fluorescence quantum yield varied from 0.008 to 0.09 as a function of environment and incident irradiance. Modeled particle backscattering coefficients were linearly related to total particle cross section over a twentyfold range in backscattering coefficents (rho = 0.996, n = 12).

Roesler, Collin S.↗
DOE OSTI2012

A CATALOG OF ROTATION AND ACTIVITY IN EARLY-M STARS

We present a catalog of rotation and chromospheric activity in a sample of 334 M dwarfs of spectral types M0-M4.5 populating the parameter space around the boundary to full convection. We obtain high-resolution optical spectra for 206 targets and determine projected rotational velocity, vsin i, and H{alpha} emission. The data are combined with measurements of vsin i in field stars of the same spectral type from the literature. Our sample adds 157 new rotation measurements to the existing literature and almost doubles the sample of available vsin i. The final sample provides a statistically meaningful picture of rotation and activity at the transition to full convection in the solar neighborhood. We confirm a steep rise in the fraction of active stars at the transition to full convection known from earlier work. In addition, we see a clear rise in rotational velocity in the same stars. In very few stars, no chromospheric activity but a detection of rotational broadening is reported. We argue that all of them are probably spurious detections; we conclude that in our sample all significantly rotating stars are active, and all active stars are significantly rotating. The rotation-activity relation is valid in partially and in fully convective stars. Thus, we do not observe any evidence for a transition from a rotationally dominated dynamo in partially convective stars to a rotation-independent turbulent dynamo in fully convective stars; turbulent dynamos in fully convective stars of spectral types around M4 are still driven by rotation. Finally, we compare projected rotational velocities of 33 stars to rotational periods derived from photometry in the literature and determine inclinations for a few of them.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

Neutron emission and fragment yield in high-energy fission

The KRIS special library of spectra and emission probabilities in the decays of 1500 nuclei excited up to energies between 150 and 250 MeV was developed for correctly taking into account the decay of highly excited nuclei appearing as fission fragments. The emission of neutrons, protons, and photons was taken into account. Neutron emission fromprimary fragments was found to have a substantial effect on the formation of yields of postneutron nuclei. The library was tested by comparing the calculated and measured yields of products originating from the fission of nuclei that was induced by high-energy protons. The method for calculating these yields was tested on the basis of experimental data on the thermal-neutroninduced fission of {sup 235}U nuclei.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2013

CYGNUS X-3's LITTLE FRIEND

Using the unique X-ray imaging capabilities of the Chandra X-ray observatory, a 2006 observation of Cygnus X-3 has provided insight into a singular feature associated with this well-known microquasar. This extended emission, located {approx}16'' from Cygnus X-3, varies in flux and orbital phase (shifted by 0.56 in phase) with Cygnus X-3, acting like a celestial X-ray 'mirror'. The feature's spectrum, flux, and time variations allow us to determine the location, size, density, and mass of the scatterer. We find that the scatterer is a Bok Globule located along our line of sight, and we discuss its relationship to Cygnus X-3. This is the first time such a feature has been identified with Chandra.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

AN INFRARED EXCESS IDENTIFIED IN RADIO-LOUD BROAD ABSORPTION LINE QUASARS

If broad absorption line (BAL) quasars represent a high-covering-fraction evolutionary state (even if this is not the sole factor governing the presence of BALs), it is expected that they should show an excess of mid-infrared radiation compared to normal quasars. Some previous studies have suggested that this is not the case. We perform the first analysis of the IR properties of radio-loud BAL quasars, using IR data from WISE and optical (rest-frame ultraviolet) data from SDSS, and compare the BAL quasar sample with a well-matched sample of unabsorbed quasars. We find a statistically significant excess in the mid- to near-infrared luminosities of BAL quasars, particularly at rest-frame wavelengths of 1.5 and 4 {mu}m. Our sample was previously used to show that BALs are observed along many lines of sight toward quasars, but with an overabundance of more edge-on sources, suggesting that orientation factors into the appearance of BALs. The evidence here-of a difference in IR luminosities between BAL quasars and unabsorbed quasars-can be ascribed to evolution. This suggests that a merging of the current BAL paradigms is needed to fully describe the class.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1986

Correcting observed stellar Lyman alpha profiles for the effects of interstellar absorption and geocoronal emission

Techniques to compensate for interstellar absorption and geocoronal emission in IUE studies of late stars atmospheres were developed. Thus it is possible to determine the Lyman alpha flux from nearby cool stars using the low-resolution spectra in the IUE archives. The accuracy of such a procedure depends fundamentally upon the assumptions regarding the shape of the intrinsic profile and the density and velocity structure of the local interstellar medium, not upon measurement uncertainties of the low-resolution spectra. Geocoronal emission and saturated spectra are fatal only to a one-dimensional spectral analysis. When both the spatial and the spectral dimensions are considered, the observed Lyman alpha flux can be recovered.

Neff, J. E.↗
NASA NTRS1967

Spectra of interstellar matter

Absorption and emission lines, continuous emission of thermal radiation, and continuous nonthermal emission of interstellar spectra

EMISSION SPECTRUM↗
DOE OSTI2017

Toward an Understanding of the Excitonic Structure of the CP47 Antenna Protein Complex of Photosystem II Revealed via Circularly Polarized Luminescence

Identification of the lowest energy pigments in the photosynthetic CP47 antenna protein complex of Photosystem II (PSII) is essential for understanding its excitonic structure, as well as excitation energy pathways in the PSII core complex. Unfortunately, there is no consensus concerning the nature of the low-energy state(s) nor chlorophyll (Chl) site energies in this important photosynthetic antenna. Although, we raised concerns regarding the estimations of Chl site energies obtained from modeling studies of various types of CP47 optical spectra [Reinot, T; et al., Anal. Chem. Insights 2016, 11, 35–48] recent new assignments imposed by the shape of the circularly polarized luminescence (CPL) spectrum [Hall, J.; et al., Biochim. Biophys. Acta 2016, 1857, 1580–1593] necessitate our comments. We demonstrate that other combinations of lowenergy Chls provide equally good or improved simultaneous fits of various optical spectra (absorption, emission, CPL, circular dichroism, and nonresonant hole-burned spectra), but more importantly, we expose the heterogeneous nature of the recently studied complexes and argue that the published composite nature of the CPL (contributed to by CPL 685 , CPL 691 , and CPL 695 ) does not represent an intact CP47 protein. A positive CPL 695 is extracted for the intact protein, which when simultaneously fitted with multiple other optical spectra, provides new information on the excitonic structure of intact and destabilized CP47 complexes and their lowest energy state(s).

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

EXPLORING THE DIVERSITY OF GROUPS AT 0.1 < z < 0.8 WITH X-RAY AND OPTICALLY SELECTED SAMPLES

We present the global group properties of two samples of galaxy groups containing 39 high-quality X-ray-selected systems and 38 optically (spectroscopically) selected systems in coincident spatial regions at 0.12 < z < 0.79. The total mass range of the combined sample is {approx}(10{sup 12}-5) Multiplication-Sign 10{sup 14} M{sub Sun }. Only nine optical systems are associable with X-ray systems. We discuss the confusion inherent in the matching of both galaxies to extended X-ray emission and of X-ray emission to already identified optical systems. Extensive spectroscopy has been obtained and the resultant redshift catalog and group membership are provided here. X-ray, dynamical, and total stellar masses of the groups are also derived and presented. We explore the effects of utilizing different centers and applying three different kinds of radial cut to our systems: a constant cut of 1 Mpc and two r{sub 200} cuts, one based on the velocity dispersion of the system and the other on the X-ray emission. We find that an X-ray-based r{sub 200} results in less scatter in scaling relations and less dynamical complexity as evidenced by results of the Anderson-Darling and Dressler-Schectman tests, indicating that this radius tends to isolate the virialized part of the system. The constant and velocity dispersion based cuts can overestimate membership and can work to inflate velocity dispersion and dynamical and stellar mass. We find L{sub X} -{sigma} and M{sub stellar}-L{sub X} scaling relations for X-ray and optically selected systems are not dissimilar. The mean fraction of mass found in stars, excluding intracluster light, for our systems is {approx}0.014 with a logarithmic standard deviation of 0.398 dex. We also define and investigate a sample of groups which are X-ray underluminous given the total group stellar mass. For these systems the fraction of stellar mass contributed by the most massive galaxy is typically lower than that found for the total population of groups implying that there may be less intragroup medium contributed from the most massive member in these systems. Eighty percent of 15 underluminous groups have less than 40% of their stellar mass in the most massive galaxy which happens in less than 1% of cases with samples matched in stellar mass, taken from the combined group catalog.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Fantastic Fits with fantasy of Active Galactic Nuclei Spectra: Exploring the Fe II Emission near the Hα Line

In this study, a refined approach for multicomponent fitting of active galactic nuclei (AGNs) spectra is presented utilizing the newly developed Python code Fully Automated pythoN Tool for AGN Spectra analYsis (fantasy). AGN spectra are modeled by simultaneously considering the underlying broken power-law continuum, predefined emission line lists, and an Fe II model, which is here extended to cover the wavelength range 3700–11000 Å. The Fe II model, founded solely on atomic data, effectively describes the extensive emission of the complex iron ion in the vicinity of the Hγ and Hβ lines, as well as near the Hα line, which was previously rarely studied. The proposed spectral fitting approach is tested on a sample of high-quality AGN spectra from the Sloan Digital Sky Survey Data Release 17. The results indicate that when Fe II emission is present near Hβ, it is also detected redward from Hα, potentially contaminating the broad Hα line wings and thus affecting the measurements of its flux and width. The production of Fe II emission is found to be strongly correlated with Eddington luminosity and appears to be controlled by a similar mechanism as the hydrogen Balmer lines. The study highlights the benefits of fitting type 1 AGN spectra with the fantasy code, pointing that it may be used as a robust tool for analyzing a large number of AGN spectra in the coming spectral surveys.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Light-curve analysis of neon novae

We analyzed light curves of five neon novae, QU Vul, V351 Pup, V382 Vel, V693 CrA, and V1974 Cyg, and determined their white dwarf (WD) masses and distance moduli on the basis of theoretical light curves composed of free–free and photospheric emission. For QU Vul, we obtained a distance of d ∼ 2.4 kpc, reddening of E(B − V) ∼ 0.55, and WD mass of M{sub WD} = 0.82–0.96 M{sub ⊙}. This suggests that an oxygen–neon WD lost a mass of more than ∼0.1 M{sub ⊙} since its birth. For V351 Pup, we obtained d∼5.5 kpc, E(B−V)∼0.45, and M{sub WD}=0.98–1.1 M{sub ⊙}. For V382 Vel, we obtained d∼1.6 kpc, E(B−V)∼0.15, and M{sub WD}=1.13–1.28 M{sub ⊙}. For V693 CrA, we obtained d∼7.1 kpc, E(B−V)∼0.05, and M{sub WD}=1.15–1.25 M{sub ⊙}. For V1974 Cyg, we obtained d∼1.8 kpc, E(B−V)∼0.30, and M{sub WD}=0.95–1.1 M{sub ⊙}. For comparison, we added the carbon–oxygen nova V1668 Cyg to our analysis and obtained d∼5.4 kpc, E(B−V)∼0.30, and M{sub WD}=0.98–1.1 M{sub ⊙}. In QU Vul, photospheric emission contributes 0.4–0.8 mag at most to the optical light curve compared with free–free emission only. In V351 Pup and V1974 Cyg, photospheric emission contributes very little (0.2–0.4 mag at most) to the optical light curve. In V382 Vel and V693 CrA, free–free emission dominates the continuum spectra, and photospheric emission does not contribute to the optical magnitudes. We also discuss the maximum magnitude versus rate of decline relation for these novae based on the universal decline law.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

SINGLE-STAR H II REGIONS AS A PROBE OF MASSIVE STAR SPECTRAL ENERGY DISTRIBUTIONS

The shape of OB-star ionizing spectral energy distributions (SEDs) is a critical component in many diagnostics of galaxy and interstellar medium properties. To quantitatively examine the shape of the OB-star SED, we compare long slit observations of single-star, Large Magellanic Cloud H II regions to the predictions from CLOUDY photoionization simulations that use CoStar, TLUSTY, and WM-basic stellar atmosphere models as the ionizing source. For each atmosphere model, we run grids of H II region simulations with the effective temperature (T{sub eff}) of the star as a free parameter. The best SEDs from each atmosphere code are found by matching the predicted emission-line spectra with those observed from the nebulae. By assuming a clumpy gas distribution, all atmosphere codes are able to reproduce the observed emission lines, except at the highest energy transitions {approx}> 40 eV. Taking into account both low and high energy transitions, we find that simulations using WM-basic produce the best agreement with the observed line ratios. The rates of ionizing photons from different atmosphere models vary systematically with the relative hardness of the SEDs. However, in general the rates produced by the model SEDs, for standard log(g) = 4.0 models, are consistent with the rates derived from the H{alpha} luminosities. We find that our effective temperatures inferred from the nebular ionization balance are consistent with those predicted by conventional photospheric-based calibrations from the literature. We suggest that future spectral type to T{sub eff} calibrations can be constructed from nebular data.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

DISENTANGLING AGN AND STAR FORMATION IN SOFT X-RAYS

We have explored the interplay of star formation and active galactic nucleus (AGN) activity in soft X-rays (0.5-2 keV) in two samples of Seyfert 2 galaxies (Sy2s). Using a combination of low-resolution CCD spectra from Chandra and XMM-Newton, we modeled the soft emission of 34 Sy2s using power-law and thermal models. For the 11 sources with high signal-to-noise Chandra imaging of the diffuse host galaxy emission, we estimate the luminosity due to star formation by removing the AGN, fitting the residual emission. The AGN and star formation contributions to the soft X-ray luminosity (i.e., L{sub x,AGN} and L{sub x,SF}) for the remaining 24 Sy2s were estimated from the power-law and thermal luminosities derived from spectral fitting. These luminosities were scaled based on a template derived from XSINGS analysis of normal star-forming galaxies. To account for errors in the luminosities derived from spectral fitting and the spread in the scaling factor, we estimated L{sub x,AGN} and L{sub x,SF} from Monte Carlo simulations. These simulated luminosities agree with L{sub x,AGN} and L{sub x,SF} derived from Chandra imaging analysis within a 3{sigma} confidence level. Using the infrared [Ne II]12.8 {mu}m and [O IV]26 {mu}m lines as a proxy of star formation and AGN activity, respectively, we independently disentangle the contributions of these two processes to the total soft X-ray emission. This decomposition generally agrees with L{sub x,SF} and L{sub x,AGN} at the 3{sigma} level. In the absence of resolvable nuclear emission, our decomposition method provides a reasonable estimate of emission due to star formation in galaxies hosting type 2 AGNs.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Photoionization Models for the Inner Gaseous Disks of Herbig Be Stars: Evidence against Magnetospheric Accretion?

We investigate the physical properties of the inner gaseous disks of three hot Herbig B2e stars, HD 76534, HD 114981, and HD 216629, by modeling CFHT-ESPaDOns spectra using non-LTE radiative transfer codes. We assume that the emission lines are produced in a circumstellar disk heated solely by photospheric radiation from the central star in order to test whether the optical and near-infrared emission lines can be reproduced without invoking magnetospheric accretion. The inner gaseous disk density was assumed to follow a simple power-law in the equatorial plane, and we searched for models that could reproduce observed lines of H i (H α and H β ), He i, Ca ii, and Fe ii. For the three stars, good matches were found for all emission line profiles individually; however, no density model based on a single power-law was able to reproduce all of the observed emission lines. Among the single power-law models, the one with the gas density varying as ∼10{sup −10}( R {sub *}/ R ){sup 3} g cm{sup −3} in the equatorial plane of a 25 R {sub *} (0.78 au) disk did the best overall job of representing the optical emission lines of the three stars. This model implies a mass for the H α -emitting portion of the inner gaseous disk of ∼10{sup −9} M {sub *}. We conclude that the optical emission line spectra of these HBe stars can be qualitatively reproduced by a ≈1 au, geometrically thin, circumstellar disk of negligible mass compared to the central star in Keplerian rotation and radiative equilibrium.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Poly(methyl methacrylate)/layered zinc sulfide nanocomposites: Preparation, characterization and the improvements in thermal stability, flame retardant and optical properties

Highlights: • Layered zinc sulfide (LZnS) was synthesized successfully via hydrothermal method. • We prepare PMMA/LZnS nanocomposites by in situ bulk polymerization of MMA. • PMMA/LZnS nanocomposites were investigated by TGA, DSC, MCC, UV–vis and PL test. • The thermal stability, flame retardant and optical properties of PMMA are improved. - Abstract: Layered zinc sulfide (LZnS) was synthesized successfully via hydrothermal method and poly(methyl methacrylate) (PMMA)/layered zinc sulfide nanocomposites were obtained by in situ bulk polymerization of methyl methacrylate (MMA). X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used to characterize the as-synthesized layered zinc sulfide and PMMA/layered zinc sulfide nanocomposites. Microscale combustion calorimeter (MCC), differential scanning calorimeter (DSC) and thermogravimetric analysis (TGA) were used to test the thermal properties of the composites. Ultraviolet visible (UV–vis) transmittance spectra and photoluminence (PL) spectra were obtained to investigate the optical properties of the composites. From the results, the thermal degradation temperature is increased by 20–50 °C, the peak of heat release rate (pHRR) and total heat release (THR) are both decreased by above 30%, and the photoluminence intensity is enhanced with the increasing loading of layered zinc sulfide.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Solar photocatalytic activities of porous Nb-doped TiO{sub 2} microspheres by coupling with tungsten oxide

Highlights: • Nb-TiO{sub 2}/WO{sub 3} was prepared by USP method combined impregnation method. • Nb-doping extend the spectral absorption of TiO{sub 2} into visible spectrum. • Nb-TiO{sub 2}/WO{sub 3} has a similar optical band gap as Nb-TiO{sub 2}. • PL spectra indicate WO{sub 3} can accept the photoexcited electrons from Nb-TiO{sub 2}. • Nb-TiO{sub 2}/WO{sub 3} shows higher activity than TiO{sub 2} and Nb-TiO{sub 2} under solar light. - Abstract: Nb doped TiO{sub 2} microspheres modified with WO{sub 3} (Nb-TiO{sub 2}/WO{sub 3}) was prepared by ultrasonic spray pyrolysis method combined with impregnation method. The microspheres were characterized with SEM, TEM, XRD, BET, photoluminescence and UV–vis absorption spectra. The Nb-doping was observed to extend the spectral absorption of TiO{sub 2} into visible spectrum, and the absorption onset was red-shifted for about 88 nm compared to pristine TiO{sub 2} microspheres. Nb-TiO{sub 2}/WO{sub 3} microspheres do not display a red-shifted absorption edge compared with Nb doped TiO{sub 2} microspheres. Under solar irradiation, Nb-TiO{sub 2}/WO{sub 3} microspheres showed higher photocatalytic activity for methylene blue degradation compared with that of pure TiO{sub 2} microspheres and Nb doped TiO{sub 2} microspheres, which could be ascribed to the extended light absorption range and the suppression of electron-hole pair recombination.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Development and characterization of PCDTBT:CdSe QDs hybrid solar cell

Solar cell consisting of low band gap polymer poly[N-900-hepta-decanyl-2,7-carbazole-alt-5,5-(40,70-di-2-thienyl-20,10, 30-benzothiadiazole)] (PCDTBT) as donor and cadmium selenide/zinc sulphide (CdSe/ZnS) core shell quantum dots (QDs) as an acceptor has been developed. The absorption measurements show that the absorption coefficient increases in bulk heterojunction (BHJ) structure covering broad absorption spectrum (200nm–700nm). Also, the photoluminescence (PL) of the PCDTBT:QDs film is found to decrease by an order of magnitude showing a significant transfer of electrons to the QDs. With this approach and under broadband white light with an irradiance of 8.19 mW/cm{sup 2}, we have been able to achieve a power conversion efficiency (PCE) of 3.1 % with fill factor 0.42 for our typical solar cell.

77 NANOSCIENCE AND NANOTECHNOLOGY↗