Search NASA⌕ Search

SEARCH · Search NASA

Results for “Spectrum Width”

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 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

Evidence for ionized hydrogen in the cores of globular clusters

Photometric and spectrographic observations of 27 globular clusters reveal evidence for the existence of an emission component of H-alpha in the cores of several globular clusters, notably NGC 5824 and the X-ray clusters NGC 1851, 6624, and 7078. UBVR measurements for all 27 clusters show that the colors of the innermost cores (out to about 8 arcsec) are marginally reddened. A time-resolved spectrum of the central 1 by 3 arcsec of the X-ray burst source globular NGC 6624 revealed a remarkable brightening of about 1 magnitude with a duration of approximately 25 min. Concurrent with this apparent flare, H-alpha emission was seen at a radial velocity of -400 km/s relative to the absorption component. Both the emission equivalent width(about 1 A) and variability are consistent with the photometric data.

Grindlay, J. E.↗
NASA NTRS1987

Hydrogen emission from Jupiter: Hydrogen emission from sunlit atmosphere of Saturn

Successful IUE observations of the equatorial sunlit atmosphere of Jupiter and Saturn have been obtained. Spectra containing atomic and molecular hydrogen and solar reflection continuum emissions have been analyzed, with the purpose of determining the long term temporal behavior of the electroglow process. Quantitative estimates have been established for the first time using a model analysis of the short wavelength region of the spectrum. Both systems show varying degrees of long term variability in hydrogen emission rate, but the time scale is too short to determine whether there is a dependence on solar cycle activity. As part of the emission modeling program, a preliminary point source spreading function for the IUE SWP instrument has been established, suggesting a wavelength dependence in spectral line width different from previous analyses. Further IUE observations are planned for both Jupiter and Saturn.

Shemansky, D. E.↗
NASA NTRS2002

Discovery of Cyclotron Resonance Features in the Soft Gamma Repeater SGR 1806-20

We report evidence for cyclotron resonance features from the Soft Gamma Repeater SCR 1806-20 in outburst, detected with the Rossi X-ray Timing Explorer in the spectrum of a long, complex precursor that preceded a strong burst. The features consist of a narrow 5.0 keV absorption line with modulation near its second and third harmonics (at 11.2 keV and 17.5 keV respectively). The line features are transient and are detected in the harder part of the precursor. The 5.0 keV feature is strong, with an equivalent width of approx. 500 eV, and a narrow width of < 0.4 keV. Interpreting the features as electron cyclotron lines in the context of accretion models leads to a large mass-radius ratio (M/R > 0.3 Solar Mass/km) that is inconsistent with neutron stars, or requires a low (5 - 7) x 10(exp 11) G magnetic field that is unlikely for SGRs. The line widths are also narrow compared to those of electron cyclotron resonances observed so far in X-ray pulsars. In the magnetar picture, the features are plausibly explained as ion cyclotron resonances in an ultra-strong magnetic field, which have recently been predicted from magnetar candidates. In this view, the 5.0 keV feature is consistent with a proton cyclotron fundamental whose energy and width are close to model predictions. The line energy would correspond to a surface magnetic field of 1.0 x 10(exp 15) G for SGR 1806-20, in good agreement with that inferred from the spin-down measure in the source.

Ibrahim, A. I.↗
NASA NTRS2002

Discovery of Cyclotron Resonance Features in the Soft Gamma Repeater SGR 1806-20

We report evidence of cyclotron resonance features from the Soft Gamma Repeater SGR 1806-20 in outburst, detected with the Rossi X-ray Timing Explorer in the spectrum of a long, complex precursor that preceded a strong burst. The features consist of a narrow 5.0 keV absorption line with modulation near its second and third harmonics (at 11.2 keV and 17.5 keV respectively). The line features are transient and are detected in the harder part of the precursor. The 5.0 keV feature is strong, with an equivalent width of approx. 500 eV and a narrow width of less than 0.4 keV. Interpreting the features as electron cyclotron lines in the context of accretion models leads to a large mass-radius ratio (M/R greater than 0.3 solar mass/km) that is inconsistent with neutron stars or that requires a low (5-7) x 10(exp 11) G magnetic field that is unlikely for SGRs. The line widths are also narrow compared with those of electron cyclotron resonances observed so far in X-ray pulsars. In the magnetar picture, the features are plausibly explained as ion cyclotron resonances in an ultra-strong magnetic field that have recently been predicted from magnetar candidates. In this view, the 5.0 keV feature is consistent with a proton cyclotron fundamental whose energy and width are close to model predictions. The line energy would correspond to a surface magnetic field of 1.0 x 10(exp 15) G for SGR 1806-20, in good agreement with that inferred from the spin-down measure in the source.

Ibrahim, Alaa I.↗
NASA NTRS1995

Degree-scale anisotropy in the cosmic microwave background: SP94 results

We present results from two observations of the cosmic microwave background (CMB) performed from the South Pole during the 1993-1994 austral summer. Each observation employed a 3 deg peak-to-peak sinusoidal, single-difference chop and consisted of a 20 deg x 1 deg strip on the sky. The first observation used a receiver which operates in three channels between 38 and 45 GHz (Q-band) with a full width half maximum (FWHM) beam which varies from 1 deg to 1.15 deg. The second observation overlapped the first observation and used a receiver which operates in four channels between 26 and 36 GHz (Ka-band) with a FWHM beam which varies from 1.5 deg to 1.7 deg. Significant correlated structure is observed in all channels for each observation. The spectrum of the structure is consistent with a CMB spectrum and is formally inconsistent with diffuse synchrotron and free-free emission at the 5 sigma level. The amplitude of the structure is inconsistent with 20 K interstellar dust; however, the data do not discriminate against flat or inverted spectrum point sources. The root mean square amplitude (+/- 1 sigma) of the combined (Ka + Q) data is Delta T(sub rms) = 41.2(sup +15.5, sub -6.7) micro-K for an average window function which has a peak value of 0.97 at l = 68 and drops to e(exp -0.5) of the peak value at l = 36 and l = 106. A band power estimate of the CMB power spectrum, C(sub l), gives average value of (C(sub l)l(l + 1)/(2 pi))(sub B) = 1.77(sup +1.58, sub -0.54) x 10(exp -10).

Gundersen, J. O.↗
NASA NTRS2000

Spectral Evolution in GRB 990510

We present time-resolved spectroscopy of the afterglow of GRB 990510. Through the identification of several absorption lines in the first epoch spectrum, we determine the redshift for this burst to be z >= 1.6190 +/- 0.0016. No clear emission lines are detected. From the absence of the Ly.alpha drop, we can put an upper limit to the redshift of z <= 2.3. We study the time evolution of the MgII absorption line in our spectra taken 0.8 and 3.9 days after the burst, whose equivalent width (E.W.) is expected to change in case the burst resides in a dense compact medium (Perna & Loeb 1998). We measure an E.W. of 2.5 /- 0.2 and 2.3 +/- 0.6 in the spectra 0.8 and 3.8 days after the burst, respectively. Our results suggest that the atoms responsible for the absorption are not in the vicinity of the site of the burst.

Vreeswijk, P. M.↗
NASA NTRS1983

Redistribution - Why half a collision is better than a whole one

The study of spectral line shapes has traditionally been mainly concerned with the measurement and interpretation of absorption or emission profiles. Often only the line widths are studied. The present investigation has the objective to evaluate the additional information which can be obtained by scattering light (usually from a laser) from an atomic system which is being perturbed by collisions. A scattering experiment is discussed. The scattered light consists of two components, a (coherent) Rayleigh component and a redistributed (fluorescent) component. In order to obtain the absorption spectrum, questions regarding the probability of photon absorption are considered. By observing the fluorescence subsequent to absorption during a collision it is found possible to obtain information on the evolution of the system from the point of absorption to the completion of the collision. The information on the intracollisional evolution is the justification for the title of the study, namely 'Why half a collision is better than a whole one'.

Cooper, J.↗
NASA NTRS1990

Analysis of pressure-broadened ozone spectra in the 3 micron region

The Molecular Spectroscopy Lab at NASA-Langley has been involved in a long term effort to carefully characterize the infrared spectra of small molecules of atmospheric interest, including methane, water vapor, ozone, and their isotopic counterparts. High resolution gas phase infrared spectra are obtained using both a tunable diode laser system, and the McMath Fourier transform spectrometer at the Kitt Peak Solar Observatory. Spectra are obtained at various pressures and temperatures for pure gas samples, and for samples containing mixtures of the species of interest in nitrogen, oxygen, or air. From these spectra, using a nonlinear least squares fitting technique, spectral parameters of position, intensity, and half-width were determined for varying laboratory conditions that approximate atmospheric conditions experienced in remote sensing situations. These parameters are of interest in theoretical studies of these species, as well as in allowing more accurate interpretation of remote sensing data. The current work involves the analysis of a series of McMath FTIR spectra of ozone broadened by mixing with air, nitrogen, or oxygen. Each spectrum covers the region from 2396 to 4057/cm. Each vibrational band is analyzed by first diving its region into small intervals containing a few well isolated absorption lines of reasonable intensity. Each of these small intervals is fit by multiple iterations of the nonlinear least square program until residuals are minimized to a reasonable value which corresponds to the noise level of the measured spectrum. Intervals for the 3 nu(sub 3) ozone band in the region from 3000 to 3060 wavenumbers are being examined.

Prochaska, Eleanor S.↗
NASA NTRS1995

Space qualification of IR-reflecting coverslides for GaAs solar cells

Improvements to GaAs solar array performance, from the use on solar cell coverslides of several reflecting coatings that reject unusable portions of the solar spectrum, are quantified. Blue-red-rejection (BRR) coverslides provide both infrared reflection (IRR) and ultraviolet rejection (UVR). BRR coverslides were compared to conventional antireflection (AR) and ultraviolet (UV) coated coverslides. A 2% improvement in peak-power output, relative to that from Ar-coated coverslides, is seen for cells utilizing BRR coverslides with the widest bandpass. Coverslide BRR-filter bandpass width and covered-solar-cell short-circuit current is a function of incident light angle and the observed narrower-bandpass filters are more sensitive to change in angle from the normal than are wide-bandpass filters. The first long-term (3000 hours) UV testing of unirradiated and 1 MeV electron-irradiated GaAs solar cells, with multilayer-coated coverslides to reduce solar array operating temperature, has indicated that all multilayer coatings on coverslides and solar cells will experience degradation from the space environment (UV and/or electrons). Five types of coverslide coatings, designed for GaAs solar cells, were tested as part of a NASA-sponsored space-flight qualification for BRR, multi-layer-coated, coverslides. The reponse to the different radiations varied with the coatings. The extent of degradation and its consequences on the solar cell electrical characteristics depend upon the coatings and the radiation. In some cases, an improved optical coupling was observed during long-term UV exposure to the optical stack. The benefits of multi-layered solar cell optics may depend upon both the duration and the radiation environment of a mission.

Meulenberg, Andrew↗
NASA NTRS2004

Iron K Lines from Accretion Disks: Models for Line Production and Spectroscopic Constraints

Measured profiles of the iron K lines provide important dynamical information about emitting matrial in compact objects. However, much of the modeling work which has been used to infer the location and origin of line observed from AGN and galactic black hole sources is based on highly simplified assumptions about the microphysics of K line emission. In particular, many of the intrinsic line energies, widths and emissivities are based on central-field atomic calculations. We present the results of new calculations of the quantities for the entire iron isonuclear sequence, and demonstrate that the intrinsic K line spectra contain considerably more complexity than has been previously considered. We also present calculations of iron K emission and absorption spectra which include the new data, including the local spectrum radiated from an X-ray illuminated accretion disk. The implications for the interpretation of observed iron K lines from black hole sources will be discussed.

Kallman, Timothy↗
NASA NTRS2011

What Supergranule Flow Models Tell Us About the Sun's Surface Shear Layer and Magnetic Flux Transport

Models of the photospheric flows due to supergranulation are generated using an evolving spectrum of vector spherical harmonics up to spherical harmonic wavenumber l~1500. Doppler velocity data generated from these models are compared to direct Doppler observations from SOHO/MDI and SDO/HMI. The models are adjusted to match the observed spatial power spectrum as well as the wavenumber dependence of the cell lifetimes, differential rotation velocities, meridional flow velocities, and relative strength of radial vs. horizontal flows. The equatorial rotation rate as a function of wavelength matches the rotation rate as a function of depth as determined by global helioseismology. This leads to the conclusions that the cellular structures are anchored at depths equal to their widths, that the surface shear layer extends to at least 70 degrees latitude, and that the poleward meridional flow decreases in amplitude and reverses direction at the base of the surface shear layer (approx.35 Mm below the surface). Using the modeled flows to passively transport magnetic flux indicates that the observed differential rotation and meridional flow of the magnetic elements are directly related to the differential rotation and meridional flow of the convective pattern itself. The magnetic elements are transported by the evolving boundaries of the supergranule pattern (where the convective flows converge) and are unaffected by the weaker flows associated with the differential rotation or meridional flow of the photospheric plasma.

Hathaway, David↗
NASA NTRS1991

A cool supergiant with anomalous behavior of the 2800 Mg II doublet

The IUE ultraviolet spectrum for a supergiant of type G Ia, HD 135345, is obtained for the wavelength region 2000-3000 A. In the spectrum, the continuum as well as the feature of the Mg II doublet at 2800 A is found to be anomalous. The observed level of continuum increases toward short wavelengths to 2000 A, verifying that this supergiant is actually a binary system with a hot companion. The anomalies in the magnesium doublet are the complete absence of the chromospheric emission and the very small equivalent width of the doublet absorption: the equivalent width is 4 A, which is 7.5 times smaller than that for a typical G5 star. The main parameters of the binary system are obtained, namely, spectral classes, effective temperatures, ratio of radii, and visible magnitudes.

Gurzadian, G. A.↗
NASA NTRS1995

Effects of prescattering attenuation of spectropolarimetric line profiles

We present the wavelength dependent linear polarization and position angle variations arising from single Thomson scattering of continuum stellar radiation in an axisymmetric, hot, planar disk, which is in bulk motion. The wavelength dependence arises through the combination of Doppler shifted line attenuation, prior to scattering, and the Doppler redistribution of the scattered radiation due to the bulk and thermal motions of the disk electrons. We find that when the scattering electrons are cold, there are large polarization and position angle variations across the resulting spectrapolarimetric absorption line profile-agreeing with previous investigations. However, when the thermal Doppler velocities of the scattering electrons are comparable to or greater than the electron bulk velocity (as is of ten the case), then the scattered line profile is broadened and the amplitude of the polarimetric variations are considerably reduced. The properties of the electron thermal smearing function are such that the equivalent width of any scattered spectrapolarimetric feature is independent on the electron temperature-a consequence of the conservation of areas under convolution. An important result of this is that for an axisymmetric circumstellar envelope the position angle variations will average to zero across any line formed through the above process. We expect that the effect of multiple line blending will yield a depolarization equivalent width is given by thesum of the individual equivalent widths and the position angle variations will average to zero. The implications of this are that the large depolarizations observed in the UV spectra of pi Aquarii, zeta Tauri and PP Carinae by the Wisconsin Ultraviolet Photo Polarimeter Experiment (WUPPE) can only be explained with prescattering attenuation of stellar flux if there are a sufficient number of multiple overlapping lines in that part of the spectrum.

Wood, Kenneth↗
NASA NTRS1976

Limb brightening on Uranus - The visible spectrum

Results are presented for pinhole and slit narrowband photoelectric area-scanning photometry of the Uranus disk at eight central wavelengths ranging from 5600 to 7500 A. The observations were undertaken to detect limb brightening on the planet and to study the nature of its disk profile as a function of geometrical albedo. A coarse analysis of the results shows that the disk must exhibit limb brightening in the two CH4 bands at 6190 and 7300 A relative to all other wavebands investigated. Except for the two CH4 bands, the shapes and widths of the images are found to be essentially identical; point-spread-function data for all wavebands indicate no significant variation in the representative Gaussian l/e width with wavelength. A fine analysis of the data reveals absolute limb brightening in the 7300-A CH4 band and absolute limb darkening in the adjacent wavebands. These results are shown to be consistent with the hypothesis that clouds are absent from the visible atmosphere of Uranus.

Price, M. J.↗
NASA NTRS1982

Infrared observations of the Uranian rings

Maps of the Uranian rings at 2.2 microns and spectrophotometric observations covering 2.0 to 2.4 and 2.9 to 3.9 microns are discussed. The maps reveal a 2:1 azimuthal brightness variation whose amplitude and phase are consistent with the width variation and apsidal precession of the epsilon ring. Comparison with models based on stellar occultation data leads to an upper limit of 0.01 on the normal optical depth of any broad (5000 km wide), diffuse component of the ring system. A significant east-west asymmetry, corresponding to a brightening of the near side of the rings relative to the far side, is unexplained. The spectrum of the rings is flat over the range 2.1 to 3.9 microns. There is no spectroscopic evidence for the presence of H2O.

Nicholson, P. D.↗
NASA NTRS1997

The X-Ray Warm Absorber in NGC 3516

The Seyfert 1 galaxy, NGC 3516 has been the subject of many absorption line studies at both ultra-violet and X-ray wavelengths. In the UV, strong, broad, variable associated metal line absorption with velocity width approximately 2000 km s(exp -1) is thought to originate in gas with N(sub H)greater than or approximately 10(exp 10)cm (exp -2) lying between 0.01 and 9 pc from the central active nucleus. The Ginga X-ray data are consistent with several possibilities: a warm absorber and a cold absorber combined either with partial covering or an unusually strong reflection spectrum. We present ROSAT observations of NGC 3516 which show a strong detection of a warm absorber dominated by a blend of 0 VII/O VIII edges at approximately 0.8 keV with N(sub H) approximately 7x10(exp 21)cm(exp -2), and U:8-12. We argue that NGC 3516 contains an outflowing 'XUV' absorber showing the presence of X-ray absorption edges which are consistent with the presence of broad absorption lines in the old IUE spectra and their disappearance in the new UV observations. Our dynamical model suggests that the O VII absorption edge will continue to weaken compared to the O VIII edge, an easily testable prediction with future missions like AXAF. Eventually the source would be transparent to the X-rays unless a new absorption system is produced.

Mathur, Smita↗
NASA NTRS2016

Lunar Phase Function at 1064 Nm from Lunar Orbiter Laser Altimeter Passive and Active Radiometry

We present initial calibration and results of passive radiometry collected by the Lunar Orbiter Laser Altimeter onboard the Lunar Reconnaissance Orbiter over the course of 12 months. After correcting for time- and temperature-dependent dark noise and detector responsivity variations, the LOLA passive radiometry measurements are brought onto the absolute radiance scale of the SELENE Spectral Profiler. The resulting photometric precision is estimated to be 5%. We leverage the unique ability of LOLA to measure normal albedo to explore the 1064 nm phase function's dependence on various geologic parameters. On a global scale, we find that iron abundance and optical maturity (quantified by FeO and OMAT) are the dominant controlling parameters. Titanium abundance (TiO2), surface roughness on decimeter to decameter scales, and soil thermo- physical properties have a smaller effect, but the latter two are correlated with OMAT, indicating that exposure age is the driving force behind their effects in a globally-averaged sense. The phase function also exhibits a dependence on surface slope at approximately 300 m baselines, possibly the result of mass wasting exposing immature material and/or less space weathering due to reduced sky visibility. Modeling the photometric function in the Hapke framework, we find that, relative to the highlands, the maria exhibit decreased backscattering, a smaller opposition effect (OE) width, and a smaller OE amplitude. Immature highlands regolith has a higher backscattering fraction and a larger OE width compared to mature highlands regolith. Within the maria, the backscattering fraction and OE width show little dependence on TiO2 and OMAT. Variations in the phase function shape at large phase angles are observed in and around the Copernican-aged Jackson crater, including its dark halo, a putative impact melt deposit. Finally, the phase function of the Reiner Gamma Formation behaves more optically immature than is typical for its composition and OMAT, suggesting the visible-to-near-infrared spectrum and phase function respond differently to the unusual regolith evolution and properties at this location. The phase difference map revealed additional geologically-influenced variations in the phase function's shape. In particular, variations were observed associated with the dark halo around Jackson crater, the impact ejecta of Copernicus and Giordano Bruno, and the Reiner Gamma Formation. For the latter, we 915 found that the phase function behaves more optically immature than the global phase function for its composition and OMAT, suggesting a difference in how the visible-to-near-IR spectrum and phase function respond to the unusual regolith evolution and properties at this location.

moon↗
NASA NTRS2016

Lunar Phase Function at 1064 Nm from Lunar Orbiter Laser Altimeter Passive and Active Radiometry

We present initial calibration and results of passive radiometry collected by the Lunar Orbiter Laser Al- timeter onboard the Lunar Reconnaissance Orbiter over the course of 12 months. After correcting for time- and temperature-dependent dark noise and detector responsivity variations, the LOLA passive radiometry measurements are brought onto the absolute radiance scale of the SELENE Spectral Profiler. The resulting photometric precision is estimated to be approximately 5%. We leverage the unique ability of LOLA to measure normal albedo to explore the 1064 nm phase function's dependence on various geologic parameters. On a global scale, we find that iron abundance and optical maturity (quantified by FeO and OMAT) are the dominant controlling parameters. Titanium abundance (TiO2 ), surface roughness on decimeter to decameter scales, and soil thermophysical properties have a smaller effect, but the latter two are correlated with OMAT, indicating that exposure age is the driving force behind their effects in a globally-averaged sense. The phase function also exhibits a dependence on surface slope at approximately 300 m baselines, possibly the result of mass wasting exposing immature material and/or less space weathering due to reduced sky visibility. Modeling the photometric function in the Hapke framework, we find that, relative to the highlands, the maria exhibit decreased backscattering, a smaller opposition effect (OE) width, and a smaller OE amplitude. Immature highlands regolith has a higher backscattering fraction and a larger OE width compared to mature highlands regolith. Within the maria, the backscattering fraction and OE width show little dependence on TiO2 and OMAT. Variations in the phase function shape at large phase angles are observed in and around the Copernican-aged Jackson crater, including its dark halo, a putative impact melt deposit. Finally, the phase function of the Reiner Gamma Formation behaves more optically immature than is typical for its composition and OMAT, suggesting the visible-to-near-infrared spectrum and phase function respond differently to the unusual regolith evolution and properties at this location.

LOLA↗