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At least 1,063 records · Page 59
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Effects of inclination angle on the spectra of X-ray binaries

Iron emission and absorption features from nine X-ray binaries are compared with a model that predicts characteristics of iron K-shell features corresponding to different viewing angles for the accretion disk. In this model, emission and absorption features arise from an accretion disk corona whose structure is computed under the assumptions of ionization, thermal, and hydrostatic balance of gas illuminated by the central continuum source. Hence the equivalent widths of the emission and absorption features are predicted without the introduction of any free parameters to control the physical conditions in the disk corona. Our data/model comparison suggests an explanation for the equivalent widths of the iron K-alpha emission and the depth of the absorption edge in terms of (1) the angle of inclination between the observer's line of sight and the plane of the accretion disk and (2) the shape of the incident source spectrum.

Vrtilek, S. D.↗
NASA NTRS2010

Mini-TES Observations of Comanche Carbonate and Its Distribution

The discovery by the Spirit rover of outcrops rich in Mg-Fe carbonate [Morris et al., 2010] represents another manifestation of a diverse aqueous history in Gusev crater. In 2005, observations by the Moessbauer spectrometer (MB) on outcrops dubbed Comanche provided initial indication of Fe-Mg carbonate that was subsequently supported by analysis of elemental data from the Alpha Particle X-ray Spectrometer (APXS). The recognition of a carbonate component in thermal infrared spectra measured by the Miniature Thermal Emission Spectrometer (Mini-TES) was significantly delayed due to dust contamination of the instrument's optics. With the implementation of a viable dust correction, the Comanche spectra were revisited and presented clear and compelling evidence for a Mg-Fe carbonate component that could be as much as a third of the total mineral abundance. The data from all three instruments in combination are best matched by Mg-Fe carbonate with an abundance of 16-34 wt%. Mini-TES spectra were acquired for 12 targets at various locations on the Comanche (4-5 m long) and Comanche Spur (1-2 m long) outcrops, the latter being the location of the MB and APXS measurements. The two outcrops are spectrally comparable and share similar morphology and texture based on color images from the Panoramic Camera (Pancam). The highest quality Mini-TES spectrum comes from the larger Comanche outcrop on a target named Saupitty. Linear least squares modeling of the Saupitty spectrum employed a library of laboratory spectra tailored for consistency with the APXS and MB data and included spectra representing Martian dust, a slope spectrum to account for any temperature determination errors, and a blackbody spectrum to account for differences in spectral contrast between the laboratory and Mini-TES spectrum. Successful modeling of the Comanche Saupitty spectrum required one or more carbonate phases to obtain a good fit. Excluding all carbonates from the full starting library more than doubled the root-mean-squared error of the model fit (0.147% vs. 0.299%). Because Mg-Fe carbonate and Ca-Mg carbonate (dolomite) are so spectrally similar over the range used for modeling, both provide a comparable fit. However, Carich carbonates like dolomite are precluded based on APXS data and are inconsistent with MB results. The Comanche carbonate rocks are stratigraphically above a set of olivine-rich volcaniclastic rocks known as Algonquin class that mantle the Haskin Ridge feature of the Columbia Hills. Based on ~50 Mini-TES observations, the Comanche outcrops are the only rocks that host abundant carbonate. However, a target at the base of the larger Comanche outcrop appears spectrally transitional between the carbonate and olivine units. This transitional spectral character applies to additional outcrops a few 10s of meters away from Comanche that also appear stratigraphically transitional. Additional work will attempt to establish whether we are seeing an alteration horizon or depositional unit associated with the emplacement Comanche carbonate.

Ruff, Steven W.↗
NASA NTRS2014

Titan Aerosol Analog Absorption Features Produced from Aromatics in the Far Infrared

We present results on the formation of Titan aerosol analogs produced via far-UV irradiation of five aromatic precursors: benzene, naphthalene, pyridine, quinoline and isoquinoline. This is the first reported evidence of far-IR emission features observed below 200 per cm in laboratory-created Titan aerosols. These laboratory studies were motivated by recent analyses of Cassini Composite Infrared Spectrometer (CIRS) spectra that show a broad aerosol emission feature in the far-IR spectral region centered near 140 per cm, which is unique to Titan's photochemically-produced aerosol. We find that all three of the aerosol analogs formed from nitrogen-containing aromatics have similar broad emission features near that of the observed CIRS far-IR aerosol spectral feature. In addition, the inclusion of 1.5% methane to that of trace amounts of benzene also gives rise to an aerosol with a weak far-IR emission feature located below 200 per cm.

atmosphere↗
NASA NTRS1982

The far-ultraviolet spectra and geometric albedos of Jupiter and Saturn

Spectra and geometric albedoes in the range 1200 to 1940 A are compiled for Jupiter and Saturn on the basis of IUE observations. The spectra of both planets are dominated by H Lyman-alpha emission line at 1216 A, although absorption bands of C2H2 are apparent at longer wavelengths, particularly in the spectrum of Saturn, and the C I line at 1657 A is also observed. Geometric albedoes show emission features corresponding to the weak H2 Lyman and Werner bands around 1230-1280 A, auroral Lyman band emission, C I emission, and C2H2 absorption from 1600 to 1900 A. A model of atmospheric absorption in homogeneously mixed atmospheres of H2 and trace molecular absorbers is then presented and fit to the Jupiter albedo, resulting in a predicted atmosphere containing C2H2 and an unidentified molecular or particulate absorber. Finally, north-south maps of Jupiter continuum emission show limb darkening, and a comparison of equatorial and polar spectra indicates a polar increase in C2H2 absorption and weaker polar H2 emissions than previously reported.

Clarke, J. T.↗
NASA NTRS1980

The distribution of S II forbidden line emission around Jupiter

Forty-six low-dispersion spectra with high temporal resolution (about 2.5 minutes) are used to investigate the distribution and intensity of the nebular S II forbidden line emission at 6716 and 6731 A around Jupiter. The emission is found to be in the form of a ring in the vicinity of the Jovian magnetic equator with radial limits between four and seven Jovian radii. It is suggested that the ring thickness is quite variable, and that the variation found in intensity with longitude is caused by preferential plasma loading of field lines associated with the Io-induced Jovian decametric bursts.

Pilcher, C. B.↗
NASA NTRS1976

Cyclotron side-band emissions from ring-current electrons

The paper examines temporal variations in electron energy spectra and pitch-angle distributions during a VLF-emission event observed by Explorer 45 in the main phase of a magnetic storm. It is noted that the observed event occurred outside the plasmasphere on the night side of the magnetosphere and that the dusk-side plasmapause had a double structure during the event. It is found that the VLF emissions consisted of two frequency bands, corresponding to the whistler and electrostatic modes, and that there was a sharp band of 'missing emissions' along frequencies equal to half the equatorial electron gyrofrequency. A peculiar pitch-angle distribution for high-energy electrons (50 to 350 keV) is noted. It is concluded that the VLF-producing particles were enhanced low-energy (about 5 keV) ring-current electrons which penetrated into the night side of the magnetosphere from the magnetotail plasma sheet and which drifted eastward after encountering the steep gradient of the geomagnetic field.

Maeda, K.↗
NASA NTRS2021

CLEAR: The Gas-phase Metallicity Gradients of Star-forming Galaxies at 0.6<z<2.6

We report on the gas-phase metallicity gradients of a sample of 238 star-forming galaxies at 0.6 < z < 2.6, measured through deep near-infrared Hubble Space Telescope slitless spectroscopy. The observations include 12 orbit depth Hubble/WFC3 G102 grism spectra taken as a part of the CANDELS Lyα Emission at Reionization (CLEAR) survey, and archival WFC3 G102+G141 grism spectra overlapping the CLEAR footprint. The majority of galaxies in this sample are consistent with having a zero or slightly positive metallicity gradient ( dZ/dR ≥ 0, i.e., increasing with radius) across the full mass range probed (8.5 < log M * / M ⊙ < 10.5). We measure the intrinsic population scatter of the metallicity gradients, and show that it increases with decreasing stellar mass—consistent with previous reports in the literature, but confirmed here with a much larger sample. To understand the physical mechanisms governing this scatter, we search for correlations between the observed gradient and various stellar population properties at fixed mass. However, we find no evidence for a correlation with the galaxy properties we consider—including star formation rates, sizes, star formation rate surface densities, and star formation rates per gravitational potential energy. We use the observed weakness of these correlations to provide material constraints for predicted intrinsic correlations from theoretical models.

Raymond C. Simons↗
NASA NTRS2015

Spectral Confusion for Cosmological Surveys of Redshifted C II Emission

Far-infrared cooling lines are ubiquitous features in the spectra of star-forming galaxies. Surveys of redshifted fine-structure lines provide a promising new tool to study structure formation and galactic evolution at redshifts including the epoch of reionization as well as the peak of star formation. Unlike neutral hydrogen surveys, where the 21 cm line is the only bright line, surveys of redshifted fine-structure lines suffer from confusion generated by line broadening, spectral overlap of different lines, and the crowding of sources with redshift. We use simulations to investigate the resulting spectral confusion and derive observing parameters to minimize these effects in pencilbeam surveys of redshifted far-IR line emission. We generate simulated spectra of the 17 brightest far-IR lines in galaxies, covering the 150-1300 μm wavelength region corresponding to redshifts 0 < z < 7, and develop a simple iterative algorithm that successfully identifies the 158 μm [C II] line and other lines. Although the [C II] line is a principal coolant for the interstellar medium, the assumption that the brightest observed lines in a given line of sight are always [C II] lines is a poor approximation to the simulated spectra once other lines are included. Blind line identification requires detection of fainter companion lines from the same host galaxies, driving survey sensitivity requirements. The observations require moderate spectral resolution 700 < R < 4000 with angular resolution between 20″ and 10′, sufficiently narrow to minimize confusion yet sufficiently large to include a statistically meaningful number of sources.

galactic evolution at redshifts↗
NASA NTRS1998

Silicate Mineralogy of the Dust in the Inner Coma of Comet C/1995 01 (Hale-Bopp) Pre- and Post-Perihelion

We present 7.6 - 13.3 microns infrared (IR) spectrophotometry (R approx. = 180 - 350) of the 10 microns silicate emission from dust in the inner coma (i.e., within a diameter of 3in.) of comet C/1995 O1 (Hale-Bopp) at four temporal epochs from 1996 October through 1997 June during Hale-Bopp s approach to, arrival at, and recession from perihelion. The HIFOGS spectra at large heliocentric distances exhibit strong emission peaks from 9.9 - 10.1 microns and at 11.2 microns. The HIFOGS spectra of Hale-Bopp taken 1996 October 07 - 14 UT are identical in shape to the ISO SWS spectrum at 2.8 AU obtained on 1996 October 06 UT. Magnesium-rich olivine was unambiguously identified due to presence of the expected 11.2 microns peak along with the matching far-IR 18 microns, 23 microns, and 33 microns peaks in the ISO SWS spectrum. In contrast, to large heliocentric distances, we find that the silicate feature at small heliocentric distances (tau(sub lambda) less than or = 1.7 AU) exhibits strong peaks at 9.3 microns, 9.9 - 10.1 microns, and 11.2 microns, and weak at 10.5 microns and 11.8 microns. We will show that the dramatic increase of the 9.3 microns and 10.0 microns peaks close to perihelion leads to the hypothesis that there are two crystalline grain components with significantly different temperatures. The hotter mineral species (including olivines) radiate over a large range of heliocentric distances at detectable leve!s. The cooler mineral species (pyroxenes) radiate on the Wien side of the blackbody, too faint to detect in the mid-infrared spectra, until close to the sun when this species radiates on the Reyleigh-Jeans tail and becomes apparent. Decomposition of the observed silicate emission features into mineral components through comparison of the height and shape of the silicate feature ("Flux/cont") derived from the cometary spectra, to optical extinctions (Qext) derived from laboratory measurements of terrestrial silicate minerals and interplanetary dust particles (IDPs) is successful for a combination of warm grains (consisting of olivines, amorphous olivines, amorphous pyroxenes, and layer-lattice silicates) and cool grains (crystalline pyroxenes).

Wooden, Diane H.↗
NASA NTRS1992

The mass and dynamics of cD clusters with cooling flows. 1: ROSAT observations of A 496

As a part of a program to determine the mass distribution of cD galaxy clusters with cooling flows, we obtained a ROSAT image of the cluster A 496. The image reveals sharply peaked emission centered on the cD galaxy. Both the peaked cooling flow emission and the more extended emission filling the cluster are centered on the cD galaxy to within 15 sec. The surface brightness profile is consistent with previous Einstein HRI observations. We measure spatially resolved spectra for the x-ray emission, and find a significant decline in temperature in the innermost 2 to 4 min. We also find a gradient in absorption due to cold neutral gas, with excess absorption, however, is far below previously reported values. We caution that this is a progress report, and that our results are preliminary.

Kriss, Gerard A.↗
NASA NTRS1987

Physics issues of gamma ray burst emissions

The critical physics issues in the interpretation of gamma-ray-burst spectra are reviewed. An attempt is made to define the emission-region parameter space satisfying the maximum number of observational and theoretical constraints. Also discussed are the physical mechanisms responsible for the bursts that are most consistent with the above parameter space.

Liang, Edison↗
NASA NTRS1982

Chromospheres of classical Cepheids

The International Ultraviolet Explorer spectra of five classical Cepheids were obtained in the short and the long wavelength regions at low dispersion, curves and emission line strengths were obtained from the low resolution spectra. The amplitudes of the light curves increase with decreasing wavelength except around 1550 A where the amplitude is surprisingly small. The emission line fluxes behave differently in the various stars and it appears that bumps in the ultraviolet light curves are related to the behavior of the chromospheres. However, the strengths of the emission lines are roughly comparable to nonvariable stars of similar temperature and luminosity. The high resolution spectra were used to study the fluxes of the emission from the Mg II h and k lines. It is found that the emission components come and go during the cycles and the behavior differs from one star to another, with generally stronger and more persistent emission at longer periods. This is compared with the times of appearance of the Ca II H and K emission features and provides insight into the way in which the chromosphere reacts to shock waves generated by the pulsation of the star.

Schmidt, E. G.↗
NASA NTRS1995

Airborne and laboratory studies of interstellar PAHs

A brief history of the observations which have led to the hypothesis that polycyclic aromatic hydrocarbons (PAH's) are the carriers of the widespread interstellar emission features near 3050, 1615, '1300' and 890 cm(exp -1) (3.29, 6.2, '7.7', and 11.2 mu m) is presented. The central role of airborne spectroscopy is stressed. The principal reason for the assignment to PAH's was the resemblance of the interstellar emission spectrum to the laboratory absorption spectra of PAH's and PAH-like materials. Since precious little information was available on the properties of PAH's in the forms that are thought to exist under interstellar conditions -isolated and ionized in the emission zones, with the smallest PAH's being dehydrogenated- there was a need for a spectral data base on PAH's taken in these states. Here, the relevant infrared spectroscopic properties of PAH's will be reviewed. These laboratory spectra show that relative band intensities are severely altered and that band frequencies shift. It is shown that these new data alleviate several of the spectroscopic criticisms previously leveled at the hypothesis.

Allamandola, L. J.↗
NASA NTRS1972

Partially autoionizing states of atomic oxygen

The Rydberg states 3d' (3Po)2,1,0 and 3s'' (3Po)2,1,0 and the inner shell transition 2s 2p5 (3Po)2,1,0, which are forbidden to autoionize on the basis of LS coupling, were observed in emission spectroscopy and in autoionization spectra produced in the photoelectron spectrum of atomic oxygen.

Samson, J. A. R.↗
NASA NTRS1976

Optical identification of A0620-00

The optical object corresponding to the transient X-ray source A0620-00 is identified. The position (1950) of this object is given to a precision of 2 sec as: right ascension 6 hr 20 min 11.2 sec, declination -0 deg 19 min 10 sec. It is noted that the object has undergone a substantial change in brightness since the X-ray source was first detected and that three low-dispersion spectra of it show no emission or absorption features. Similarities between the present object and Sco X-1 are discussed.

Boley, F.↗
NASA NTRS1978

Dynamics of the solar transition zone

Time-resolved profiles of the 1548-A C IV line arising from the solar transition region are analyzed in order to determine whether the 300-sec oscillations characteristic of the photosphere and chromosphere penetrate into the transition zone and to measure the rms amplitude of transition-zone disturbances as well as their dependence on solar activity. The rms velocity amplitude is used to set limits on the mechanical energy flux available for solar heating. A power-spectrum analysis indicates that acoustic waves appear to have been detected in the transition zone, that at least one case of a strong 200- to 300-sec oscillation was observed, but that strong periodicities are not found on the average in either the intensity or the velocity field. It is suggested that the rms velocity that may be attributed to directly observable wave motion is between 3 and 7 km/s, depending on whether the individual emission elements seen in rocket spectra are coherent or independent in phase.

Bruner, E. C., Jr.↗