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At least 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

X-ray studies of coeval star samples. III - X-ray emission in the Ursa Major stream

Results are reported from a comprehensive survey of X-ray emission from stars known or suspected to be members of the UMa cluster and/or stream. Of the 42 UMa member stars surveyed, 18 were detected as X-ray sources, and spectral analysis was performed for 10 stars with sufficient X-ray counts. Consideration is given to relations between X-ray luminosity, color, and kinematics of the sample stars, and the X-ray spectra of the UMa stars are discussed in the context of the general problem of stellar X-ray temperatures. Also confirmed is the lack of X-ray-emitting A dwarfs among UMa members; among stars of later spectra type there is a rather large dispersion in X-ray luminosity. This dispersion cannot readily be explained by contamination with field star interlopers and appears rather to be a property of the UMa X-ray luminosity distribution function.

Schmitt, J. H. M. M.↗
NASA NTRS1993

Flow dynamics and bending of wide-angle tailed radio sources

The dynamics of tailed radio sources (WATs) is studied on the basis of VLA observations of 11 wide-angle WATs at 6 and 20 cm. These new images, in conjunction with optical and X-ray data, are used to describe the unifying characteristics of this class. WATs are found in centers of clusters without cooling cores, associated with galaxies of low space velocity. They are large sources, extending at least 50 kpc from the cluster center, and they have radio power close to the Fanaroff-Riley I/II break. The surface brightness and spectral distributions are used to model the flow fields and bending dynamics of the sources. Two limiting models are employed: the adiabatic model, in which no in situ energization takes place, and the kinetic model, in which all of the radio luminosity comes from in situ energization. It is found that the sources cannot be bent by the slow galaxy motion in the kinetic model. The sources can be bent by the ram pressure of a slowly moving central galaxy in the adiabatic model.

O'Donoghue, Aileen A.↗
NASA NTRS1994

Infrared observations of the dark matter lens candidate Q2345+007

Deep K-band observations are presented of the double image quasar Q2345+007. This has the largest separation (7.1 sec) of any quasar image pair considered as gravitationally lensed, so the required lens is massive (10(exp 13) solar masses). No lens has been detected in previous deep images at visible wavelengths, and we find no lens to limiting K magnitude 20.0 in the infrared image. This constrains any lens to being much less luminous than brightest cluster galaxies, while the lens must be much more massive than such galaxies to produce the observed separation. Because spectral data indicate exceptional intrinsic similarity in the quasar image components, this pair remains as the most intriguing example of an observed configuration requiring the presence of massive, concentrated dark matter acting as a gravitational lens.

Mcleod, Brian↗
NASA NTRS1975

Metal-to-metal charge transfer transitions - Interpretation of visible-region spectra of the moon and lunar materials

Prominent bands in the spectral profiles of Fe-Ti phases in lunar samples have been attributed to charge-transfer transitions between Fe and Ti cations, and a model is presented for calculating charge transfer energies from energy levels computed by the SCF-X(alpha) scattered wave molecular orbital method for isolated MO6 octahedral coordination clusters containing Fe(2+), Fe(3+), Ti(3+), and Ti(4+) cations. The calculated charge transfer energy for the Fe(2+) to Ti(4+) transition correlates well with a measured spectral feature around 0.6 micron in ilmenite, and, since ilmenite is a major constituent of mare basalts and dark-mantling material, the observed darkness and blueness of the regolith in lunar black spots is attributed primarily to this transition. The Ti(3+) to Ti(4+) transition is thought to contribute to some phases.

Loeffler, B. M.↗
NASA NTRS1994

Classification of asteroid spectra using a neural network

The 52-color asteroid survey (Bell et al., 1988) together with the 8-color asteroid survey (Zellner et al., 1985) provide a data set of asteroid spectra spanning 0.3-2.5 micrometers. An artificial neural network clusters these asteroid spectra based on their similarity to each other. We have also trained the neural network with a categorization learning output layer in a supervised mode to associate the established clusters with taxonomic classes. Results of our classification agree with Tholen's classification based on the 8-color data alone. When extending the spectral range using the 52-color survey data, we find that some modification of the Tholen classes is indicated to produce a cleaner, self-consistent set of taxonomic classes. After supervised training using our modified classes, the network correctly classifies both the training examples, and additional spectra into the correct class with an average of 90% accuracy. Our classification supports the separation of the K class from the S class, as suggested by Bell et al. (1987), based on the near-infrared spectrum. We define two end-member subclasses which seem to have compositional significance within the S class: the So class, which is olivine-rich and red, and the Sp class, which is pyroxene-rich and less red. The remaining S-class asteroids have intermediate compositions of both olivine and pyroxene and moderately red continua. The network clustering suggests some additional structure within the E-, M-, and P-class asteroids, even in the absence of albedo information, which is the only discriminant between these in the Tholen classification. New relationships are seen between the C class and related G, B, and F classes. However, in both cases, the number of spectra is too small to interpret or determine the significance of these separations.

Howell, E. S.↗
NASA NTRS1977

Applications of remote sensing, volume 2

The author has identified the following significant results. The overall spectral response of the strata measured by a mean vector and covariance matrix for each stratum did not show differences among the LACIE phase 3 strata using the machine clustering procedures. This was expected since the large strata gave rise to broad normal distributions with a great deal of overlap. The static stratification of Kansas contains strata which are small in size. The distributions for these strata are not as broad as those based on the LACIE phase 3 partitions, but there is still some confusion since strata from different categories are not spectrally distinct.

Landgrebe, D. A.↗
NASA NTRS1974

The extended X-ray source in Virgo and its relation to M87

Spectral data in the 0.2-1.6 keV range are presented for the extended X-ray source in the Virgo cluster. When combined with Uhuru data, the simplest function which fits the composite spectrum from 0.2 to 10 keV is one describing bremsstrahlung from an isothermal plasma at 36 million deg K. Production of the X-rays by inverse compton scattering is also considered, and models relating the X-ray source to M87 are discussed.

Catura, R. C.↗
NASA NTRS1975

Study of the utilization of EREP data from the Wabash River Basin

The author has identified the following significant results. Analysis of the digitized SL/4 S190A color IR photography proved very difficult. An area within Allen County, including Ft. Wayne, was studied. Eight segments of the study area were clustered separately and the cluster maps were then compared with the photography and maps available. The training areas for the land use classes were selected from the cluster maps. The separability measures (transformed divergence) of the classes indicated that many of the land use classes were not spectrally separable. The classification results bore this out. Visually the resulting classification map was poor, with 67 percent correct data. These results were of significantly lower quality than those obtained for the summertime SL/2 data near Lake Monroe, Indiana. Low contrast between land use classes during the wintertime and the limited spectral range and resolution are the major causes for the poor performance.

Silva, L. F.↗
NASA NTRS1976

Uhuru observations of the Norma X-ray burster

Four X-ray bursts consistent with a single source in Norma are reported which were discovered by reexamining Uhuru data obtained between 1970 and 1973. The temporal and spectral characteristics of the bursts are described and shown to be similar to those displayed by bursts from the globular cluster NGC 6224. An error box of the source location is given, and it is found that both the position and intensity of the four bursts are consistent with those of 10 bursts detected by the Vela satellites in 1976. It is concluded that the source is the same as that observed by the Vela and is an X-ray burster with characteristics similar to those of certain other bursters. XB 1608-52 is suggested as the designation of this burster, possible burst models are considered, and it is noted that the error box of the present source contains an identified globular cluster.

Grindlay, J.↗
NASA NTRS1992

The Objective Double Crystal Spectrometer

The solar corona, supernova remnants, the hot diffuse interstellar gas in the Galaxy, galactic halos, and the hot intracluster gas in rich clusters of galaxies, are examples of extended astrophysical plasmas which emit line-rich spectra in the X-ray spectral range from 1.5 to 25 A. These phenomena represent a significant fraction of the baryonic matter in the universe. The study of the composition, structure and dynamics of these astrophysical plasmas requires observations with both high spectral and spatial resolution simultaneously. The Objective Double Crystal Spectrometer, coupled with a grazing incidence X-ray telescope, represents a stigmatic instrument which is highly efficient for the study of such sources. We describe the configuration and performance (spatial resolution, spectral resolution and efficiency) of the Objective Double Crystal spectrometer.

Walker, Arthur B. C., Jr.↗
NASA NTRS2009

The Balloon Experimental Twin Telescope for Infrared Interferometry

Astronomical studies at infrared wavelengths have dramatically improved our understanding of the universe, and observations with Spitzer, the upcoming Herschel mission, and SOFIA will continue to provide exciting new discoveries. The comparatively low spatial resolution of these missions, however, is insufficient to resolve the physical scales on which mid- to far-infrared emission arises, resulting in source and structure ambiguities that limit our ability to answer key science questions. Interferometry enables high angular resolution at these wavelengths. We have proposed a new high altitude balloon experiment, the Balloon Experimental Twin Telescope for Infrared Interferometry (BETTII). High altitude operation makes far-infrared (30- 300micron) observations possible, and BETTII's 8-meter baseline provides unprecedented angular resolution (approx. 0.5 arcsec) in this band. BETTII will use a double-Fourier instrument to simultaneously obtain both spatial and spectral information. The spatially resolved spectroscopy provided by BETTII will address key questions about the nature of disks in young cluster stars and active galactic nuclei and the envelopes of evolved stars. BETTII will also lay the groundwork for future space interferometers.

Silverburg, Robert↗
NASA NTRS2012

A New Method to Constrain Supernova Fractions Using X-ray Observations of Clusters of Galaxies

Supernova (SN) explosions enrich the intracluster medium (ICM) both by creating and dispersing metals. We introduce a method to measure the number of SNe and relative contribution of Type Ia supernovae (SNe Ia) and core-collapse supernovae (SNe cc) by directly fitting X-ray spectral observations. The method has been implemented as an XSPEC model called snapec. snapec utilizes a single-temperature thermal plasma code (apec) to model the spectral emission based on metal abundances calculated using the latest SN yields from SN Ia and SN cc explosion models. This approach provides a self-consistent single set of uncertainties on the total number of SN explosions and relative fraction of SN types in the ICM over the cluster lifetime by directly allowing these parameters to be determined by SN yields provided by simulations. We apply our approach to XMM-Newton European Photon Imaging Camera (EPIC), Reflection Grating Spectrometer (RGS), and 200 ks simulated Astro-H observations of a cooling flow cluster, A3112.We find that various sets of SN yields present in the literature produce an acceptable fit to the EPIC and RGS spectra of A3112. We infer that 30.3% plus or minus 5.4% to 37.1% plus or minus 7.1% of the total SN explosions are SNe Ia, and the total number of SN explosions required to create the observed metals is in the range of (1.06 plus or minus 0.34) x 10(exp 9), to (1.28 plus or minus 0.43) x 10(exp 9), fromsnapec fits to RGS spectra. These values may be compared to the enrichment expected based on well-established empirically measured SN rates per star formed. The proportions of SNe Ia and SNe cc inferred to have enriched the ICM in the inner 52 kiloparsecs of A3112 is consistent with these specific rates, if one applies a correction for the metals locked up in stars. At the same time, the inferred level of SN enrichment corresponds to a star-to-gas mass ratio that is several times greater than the 10% estimated globally for clusters in the A3112 mass range.

Observations↗
NASA NTRS2023

The High Energy X-Ray Probe (HEX-P): Galactic PeVatrons, Star Clusters, Superbubbles, Microquasar Jets, and Gamma-Ray Binaries

HEX-P is a probe-class mission concept that will combine high spatial resolution X-ray imaging (<10"FWHM) and broad spectral coverage (0.2--80 keV) with an effective area far superior to current facilities (including XMM-Newton and NuSTAR) to enable revolutionary new insights into a variety of important astrophysical problems. With the recent discoveries of over 40 ultra-high-energy gamma-ray sources (detected above 100 TeV) and neutrino emission in the Galactic Plane, we have entered a new era of multi-messenger astrophysics facing the exciting reality of Galactic PeVatrons. In the next decade, as more Galactic PeVatrons and TeV gamma-ray sources are expected to be discovered, the identification of their acceleration and emission mechanisms will be the most pressing issue in both particle and high-energy astrophysics. In this paper, along with its companion papers (Reynolds et al. 2023, Mori et al. 2023), we will present that HEX-P is uniquely suited to address important problems in various cosmic-ray accelerators, including Galactic PeVatrons, through investigating synchrotron X-ray emission of TeV--PeV electrons produced by both leptonic and hadronic processes. For Galactic PeVatron candidates and other TeV gamma-ray sources, HEX-P can fill in a large gap in the spectral-energy distributions (SEDs) of many objects observed in radio, soft X-rays, and gamma rays, constraining the maximum energies to which electrons can be accelerated, with implications for the nature of the Galactic PeVatrons and their contributions to the spectrum of Galactic cosmic rays beyond the knee at $\sim3$ PeV. In particular, X-ray observation with HEX-P and TeV observation with CTA will provide the most powerful multi-messenger diagnostics to identify Galactic PeVatrons and explore a variety of astrophysical shock mechanisms. We present simulations of each class of Galactic TeV--PeV sources, demonstrating the power of both the imaging and spectral capabilities of HEX-P to advance our knowledge of Galactic cosmic-ray accelerators. In addition, we discuss HEX-P’s unique and complementary roles to upcoming gamma-ray and neutrino observatories in the 2030s.

particle accelerators↗
NASA NTRS2022

A Candle in the Wind: A Radio Filament in the Core of the A3562 Galaxy Cluster

Using a MeerKAT observation of the galaxy cluster A3562 (a member of the Shapley Supercluster), we have discovered a narrow, long and straight, very faint radio filament, which branches out at a straight angle from the tail of a radio galaxy located in projection near the core of the cluster. The radio filament spans 200 kpc and aligns with a sloshing cold front seen in the X-rays, staying inside the front in projection. The radio spectral index along the filament appears uniform (within large uncertainties) atα' −1.5. We propose that the radio galaxy is located outside the cold front, but dips its tail under the front. The tangential wind that blows there may stretch the radio plasma from the radio galaxy into a filamentary structure. Some reacceleration is needed in this scenario to maintain the radio spectrum uniform. Alternatively, the cosmic ray electrons from that spot in the tail can spread along the cluster magnetic field lines, straightened by that same tangential flow, via anomalously fast diffusion. Our radio filament can provide constraints on this process. We also uncover a compact radio source at the Brightest Cluster Galaxy (BCG) that is 2–3 orders of magnitude

S Giacintucci↗
NASA NTRS1993

The Evolution of Stellar Coronae: Initial Results from a ROSAT PSPC Observation of IC 2391

A 23 ks ROSAT PSPC image of the young star cluster, IC 2391, reveals 76 soft x-ray sources with L(sub x)(0.2-2.0 keV) greater than or equal to 2 x 10(exp 28) ergs/s in the direction of the cluster center. Nineteen of these sources are associated with known cluster members. We find that x-ray emission from the IC 2391 B stars deviates widely from the L(sub x)/L(sub bol) = 10(exp -7) relation based on Einstein observations of O and early B stars. Instead, we observe a wide range in L(sub x) with an order of magnitude spread at any given mass and no apparent dependence on spectral type. A comparison of the spread of L(sub x) as a function of B-V for low-mass stars between IC 2391 and the much older Hyades cluster shows that despite the factor of approx. 10 difference in their ages, these two clusters exhibit very similar dispersions in levels of stellar activity. We conclude that the low-mass stars in IC 2391 have arrived on the ZAMS with a wide range of coronal activity levels, from very strong to very weak, and that existing empirical activity-age scaling laws therefore cannot be valid.

Patten, Brian M.↗
NASA NTRS1974

Progress in gamma ray burst astronomy

Spectral observations on nine of the eleven known cosmic gamma ray bursts detected from IMP-7 from late 1972 through 1973 are reported. All nine events were found to have average spectra ranging from 100 to 1100 keV. The hypothesis of a single greater than 100 keV average event spectrum for all gamma ray bursts (inferred from IMP-6 observations) was investigated. In addition to the mutual consistency of these 14 IMP events, all independently reported average event spectra fit the IMP-7 common spectrum. This observed lack of variability of the average event spectrum suggests that the production mechanism is tied to more rigidly fixed source parameters than most celestial or solar hard X-ray phenomena. Other characteristics of gamma ray bursts events, are discussed: a high-energy spectral tail with power-law index -2.5, a rising size spectrum from the earlier event rate, and a hint of clustering of event occurrence in time.

Cline, T. L.↗
NASA NTRS1974

Satellite detection of air pollutants

NASA's ERTS-1 satellite, with its high resolution and multispectral capabilities, has been found useful in the detection and analysis of smoke from large point sources (power plants, steel mills, etc.), and widespread atmospheric turbidity associated with atmospheric stagnations. Smoke plumes from the Chicago-Northern Indiana industrial complex have been tracked over Lake Michigan for over 100 km. Experience has shown that smoke plumes are relatively easy to detect over water (in the 0.6-0.7 micrometer band) but much more difficult over land surfaces. Pattern recognition techniques (cluster analysis) were applied to the digital ERTS data, and it was found that the smoke plumes indeed had a unique spectral signature. Studies are currently underway to use measured plume geometries to obtain quantitative estimates of diffusion over water surfaces.

Lyons, W. A.↗
NASA NTRS1989

Data compression experiments with LANDSAT thematic mapper and Nimbus-7 coastal zone color scanner data

A case study is presented where an image segmentation based compression technique is applied to LANDSAT Thematic Mapper (TM) and Nimbus-7 Coastal Zone Color Scanner (CZCS) data. The compression technique, called Spatially Constrained Clustering (SCC), can be regarded as an adaptive vector quantization approach. The SCC can be applied to either single or multiple spectral bands of image data. The segmented image resulting from SCC is encoded in small rectangular blocks, with the codebook varying from block to block. Lossless compression potential (LDP) of sample TM and CZCS images are evaluated. For the TM test image, the LCP is 2.79. For the CZCS test image the LCP is 1.89, even though when only a cloud-free section of the image is considered the LCP increases to 3.48. Examples of compressed images are shown at several compression ratios ranging from 4 to 15. In the case of TM data, the compressed data are classified using the Bayes' classifier. The results show an improvement in the similarity between the classification results and ground truth when compressed data are used, thus showing that compression is, in fact, a useful first step in the analysis.

Tilton, James C.↗