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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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

Source and event selection for radio-planetary frame-tie measurements using the Phobos Landers

The Soviet Phobos Lander mission will place two spacecraft on the Martian moon Phobos in 1989. Measurements of the range from Earth-based stations to the landers will allow an accurate determination of the ephemerides of Phobos and Mars. Delta Very Long Base Interferometry (VLBI) between the landers and compact radio sources nearby on the sky will be used to obtain precise estimates of the angular offset between the radio and planetary reference frames. The accuracy of this frame-tie estimate is expected to be in the vicinity of 10 mrad, depending on how well several error sources can be controlled (calibrated or reduced). Many candidate radio sources for VLBI measurements were identified, but additional work is necessary to select those sources which have characteristics appropriate to the present application. Strategies for performing the source selection are described.

Linfield, R.↗
NASA NTRS1990

Identifying galaxies in the zone of avoidance

A set of IR color criteria was applied to sources in the IRAS Point Source Catalog at low Galactic latitudes in order to select candidate galaxies. A total of 371 of the selected sources within a Galactic latitude range (b) = 2-16 deg were searched for H I with the Arecibo 305 m radio telescope. Twenty-six percent (97) were detected, including 36 galaxies previously known only as IRAS sources. The H I spectra of the detected galaxies are presented together with their observed redshifts and velocity widths.

Lu, N. Y.↗
NASA NTRS2006

Microshutter Arrays for the JWST NIRSpec

A primary goal of the James Webb Space Telescope (JWST) is to characterize the birth and evolution of galaxies by imaging and spectroscopic observations. The telescope will use a Near Infrared Camera and a Near Infrared Spectrometer (NIRSpec) to carry out this program. The 3.6 x 3.6 field of NIRSpec will contain thousands of candidate high redshift galaxies. With such a high candidate object density, simultaneous multi-object capability is essential. This capability requires a programmable object selection mask to eliminate sky background and to reduce source confusion caused. We are developing a two-dimensional programmable field mask for NIRSpec. These masks employ micromechanical (MEMS) techniques to provide source selection over the NIRSpec field of view. The first flight format arrays (171x365 shutters) have been fabricated and full functionality of these arrays has been demonstrated in lab tests. Qualification tests are in progress to demonstrate readiness for flight, and will be complete in the early fall of 2006. In this paper, I describe performance of this critical new technology, and progress in making the devices ready for a 2008 delivery to ESA for inclusion in the NIRSpec.

Moseley, Samuel H.↗
NASA NTRS2010

Microshutter Arrays for the JWST NIRSpec

A primary goal of the James Webb Space Telescope (JWST) is to characterize the birth and evolution of galaxies by imaging and spectroscopic observations. The telescope will use a Near Infrared Camera and a Near Infrared Spectrometer (NIRSpec) to carry out this program. The 3.6' x 3.6' field of NIRSpec will contain thousands of candidate high redshift galaxies. With such a high candidate object density, simultaneous multi-object capability is essential. This capability requires a programmable object selection mask to eliminate sky background and to reduce source confusion caused. We are developing a two-dimensional programmable field mask for NIRSpec. These masks employ micromechanical (MEMS) techniques to provide source selection over the NIRSpec field of view. The first flight format arrays (171x365 shutters) have been fabricated and full functionality of these arrays has been demonstrated in lab tests.

Moseley, Samuel H.↗
NASA NTRS1994

The second Caltech-Jodrell Bank VLBI survey. 1: Observations of 91 of 193 sources

We define the sample for the second Caltech-Jodrell Bank very long base interferometry (VLBI) survey. This is a sample of 193 flat- or gigahertz-peaked-spectrum sources selected at 4850 MHz. This paper presents images of 91 sources with a resolution of approximately 1 mas, obtained using VLBI observations at 4992 MHz with a global array. The remaining images and the integrated radio spectra will be presented in a forthcoming paper by Henstock et al.

Taylor, G. B.↗
NASA NTRS2014

A Measurement of the Millimeter Emission and the Sunyaev-Zel'dovich Effect Associated with Low-Frequency Radio Sources

We present a statistical analysis of the millimeter-wavelength properties of 1.4 GHz-selected sources and a detection of the Sunyaev-Zel'dovich effect associated with the halos that host them. We stack data at 148, 218 and 277 GHz from the Atacama Cosmology Telescope at the positions of a large sample of radio AGN selected at 1.4 GHz. The thermal Sunyaev-Zel'dovich (SZ) effect associated with the halos that host the AGN is detected at the 5 sigma level through its spectral signature, representing a statistical detection of the SZ effect in some of the lowest mass halos (average M(sub 200) approximately equals 10(sup 13) solar mass h(sub 70)(exp −1) ) studied to date. The relation between the SZ effect and mass (based on weak lensing measurements of radio galaxies) is consistent with that measured by Planck for local bright galaxies. In the context of galaxy evolution models, this study confirms that galaxies with radio AGN also typically support hot gaseous halos. Adding Herschel observations allows us to show that the SZ signal is not significantly contaminated by dust emission. Finally, we analyze the contribution of radio sources to the angular power spectrum of the cosmic microwave background.

radio continuum↗
DOE OSTI2015

Coupling an electrospray source and a solids probe/chemical ionization source to a selected ion flow tube apparatus

A new ion source region has been constructed and attached to a variable temperature selected ion flow tube. The source features the capabilities of electron impact, chemical ionization, a solids probe, and electrospray ionization. The performance of the instrument is demonstrated through a series of reactions from ions created in each of the new source regions. The chemical ionization source is able to create H{sub 3}O{sup +}, but not as efficiently as similar sources with larger apertures. The ability of this source to support a solids probe, however, greatly expands our capabilities. A variety of rhenium cations and dications are created from the solids probe in sufficient abundance to study in the flow tube. The reaction of Re{sup +} with O{sub 2} proceeds with a rate constant that agrees with the literature measurements, while the reaction of Re{sub 2}{sup 2+} is found to charge transfer with O{sub 2} at about 60% of the collision rate; we have also performed calculations that support the charge transfer pathway. The electrospray source is used to create Ba{sup +}, which is reacted with N{sub 2}O to create BaO{sup +}, and we find a rate constant that agrees with the literature.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

List-Mode source injection algorithm for detectors with arbitrary pose and trajectory

environments, introducing actual sources is usually neither feasible nor economical. It is more practical to move the detector (whether airborne, vehicle-borne, or human-portable) through the test environment and then later artificially superimpose either measured or simulated source signatures on the recorded background data. We present a source injection (SI) algorithm that inserts source events into list-mode background data. It is designed to accommodate cases where “injection data” are available only at a limited set of locations. Stochastic methods are employed both to select source events from a measured dataset containing both source and background events, and to scale the number of selected events to match the field conditions of detector-source distance, air attenuation, acquisition duration, and the relative strength of the measured and injected sources. The algorithm is deployed as part of the Airborne Radiation Enhanced-sensor System (ARES) Advanced Technology Demonstration, and is applied to field data obtained using the ARES detector system. For this helicopter-borne detection system, we describe a practical ground-based measurement scheme for acquiring data for later injection. These data are then injected into background data acquired during flight, where arbitrary detector poses and trajectories are possible. Similar flight paths are traversed with and without actual 137Cs and 60Co sources present. SI is applied to the source-absent datasets, and the results are compared to the source-present datasets. SI output is found to be consistent with measured activity within the estimated uncertainties in GPS position and source strength.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRS1996

Optical detector calibrator system

An optical detector calibrator system simulates a source of optical radiation to which a detector to be calibrated is responsive. A light source selected to emit radiation in a range of wavelengths corresponding to the spectral signature of the source is disposed within a housing containing a microprocessor for controlling the light source and other system elements. An adjustable iris and a multiple aperture filter wheel are provided for controlling the intensity of radiation emitted from the housing by the light source to adjust the simulated distance between the light source and the detector to be calibrated. The geared iris has an aperture whose size is adjustable by means of a first stepper motor controlled by the microprocessor. The multiple aperture filter wheel contains neutral density filters of different attenuation levels which are selectively positioned in the path of the emitted radiation by a second stepper motor that is also controlled by the microprocessor. An operator can select a number of detector tests including range, maximum and minimum sensitivity, and basic functionality. During the range test, the geared iris and filter wheel are repeatedly adjusted by the microprocessor as necessary to simulate an incrementally increasing simulated source distance. A light source calibration subsystem is incorporated in the system which insures that the intensity of the light source is maintained at a constant level over time.

Strobel, James P.↗
NASA NTRS1980

A computer program for the prediction of near field noise of aircraft in cruising flight: User's guide

Detailed instructions for using the near field cruise noise prediction program, a program listing, and a sample case with output are presented. The total noise for free field lossless conditions at selected observer locations is obtained by summing the contributions from up to nine acoustic sources. These noise sources, selected at the user's option, include the fan/compressor, turbine, core (combustion), jet, shock, and airframe (trailing edge and turbulent boundary layers). The effects of acoustic suppression materials such as engine inlet treatment may also be included in the noise prediction. The program is available for use on the NASA/Langley Research Center CDC computer. Comparisons of the program predictions with measured data are also given, and some possible reasons for their lack of agreement presented.

Tibbetts, J. G.↗
DOE OSTI2016

The 2 Ms Chandra Deep Field-North Survey and the 250 Ks extended Chandra Deep Field-South Survey: Improved point-source catalogs

We present improved point-source catalogs for the 2 Ms Chandra Deep Field-North (CDF-N) and the 250 ks Extended Chandra Deep Field-South (E-CDF-S) Surveys, implementing a number of recent improvements in Chandra source-cataloging methodology. For CDF-N/E-CDF-S, we provide a main catalog that contains 683/1003 X-ray sources detected with wavdetect at a false-positive probability threshold of 10{sup −5} that also satisfy a binomial-probability source-selection criterion of P<0.004/P < 0.002. Such an approach maximizes the number of reliable sources detected: a total of 196/275 main-catalog sources are new compared to the Alexander et al. CDF-N/Lehmer et al. E-CDF-S main catalogs. We also provide CDF-N/E-CDF-S supplementary catalogs that consist of 72/56 sources detected at the same wavdetect threshold and having P of 0.004–0.1/0.002–0.1 and K{sub s}⩽22.9/K{sub s}⩽22.3 mag counterparts. For all ≈1800 CDF-N and E-CDF-S sources, including the ≈500 newly detected ones (these being generally fainter and more obscured), we determine X-ray source positions utilizing centroid and matched-filter techniques; we also provide multiwavelength identifications, apparent magnitudes of counterparts, spectroscopic and/or photometric redshifts, basic source classifications, and estimates of observed active galactic nucleus and galaxy source densities around respective field centers. Simulations show that both the CDF-N and E-CDF-S main catalogs are highly reliable and reasonably complete. Background and sensitivity analyses indicate that the on-axis mean flux limits reached represent a factor of ≈1.5–2.0 improvement over the previous CDF-N and E-CDF-S limits. We make our data products publicly available.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1988

Spectroscopic observations of X-ray selected late type stars

A spectroscopic survey of nine X-ray selected late type stars was conducted. These stars are serendipitously discovered EINSTEIN X-ray sources, selected from two large x-ray surveys: the Columbia Astrophysical Laboratory survey (five stars) and the CFA Medium Sensitivity survey (four stars). Four of the Columbia survey stars were found to be short period binaries. The fifth was found to be an active single G dwarf. None of the Medium Sensitivity survey stars were found to be either binaries or active stars. Activity was measured by comparing the H-alpha and the CaII infrared triplet (8498, 8542) lines in these stars to the lines in inactive stars of similar spectral type. A correlation was found between the excess H-alpha lime emission and V sin(i) and between the excess H-alpha line emission and X-ray luminosity. No correlation was found between the infrared line emission and any other measured quantity.

Takalo, L. O.↗
DOE OSTI2022

The miniJPAS survey: A search for extreme emission-line galaxies

Context. Galaxies with extreme emission lines (EELGs) may play a key role in the evolution of the Universe, as well as in our understanding of the star formation process itself. For this reason an accurate determination of their spatial density and fundamental properties in different epochs of the Universe will constitute a unique perspective towards a comprehensive picture of the interplay between star formation and mass assembly in galaxies. In addition to this, EELGs are also interesting in order to explain the reionization of the Universe, since their interstellar medium (ISM) could be leaking ionizing photons, and thus they could be low z, analogous of extreme galaxies at high z . Aims. This paper presents a method to obtain a census of EELGs over a large area of the sky by detecting galaxies with rest-frame equivalent widths ≥300 Å in the emission lines [O II]λλ3727,3729Å, [O III]λ5007Å, and Hα. For this, we aim to use the J-PAS survey, which will image an area of ≈8000 deg 2 with 56 narrow band filters in the optical. As a pilot study, we present a methodology designed to select EELGs on the miniJPAS images, which use the same filter dataset as J-PAS, and thus will be exportable to this larger survey. Methods. We make use of the miniJPAS survey data, conceived as a proof of concept of J-PAS, and covering an area of ≈1 deg 2 . Objects were detected in the r SDSS images and selected by imposing a condition on the flux in a given narrow-band J-PAS filter with respect to the contiguous ones, which is analogous to requiring an observed equivalent width larger than 300 Å in a certain emission line within the filter bandwidth. The selected sources were then classified as galaxies or quasi-stellar objects (QSOs) after a comparison of their miniJPAS fluxes with those of a spectral database of objects known to present strong emission lines. This comparison also provided a redshift for each source, which turned out to be consistent with the spectroscopic redshifts when available (|Δz/(1 + z spec )| ≤ 0.01). Results. The selected candidates were found to show a compact appearance in the optical images, some of them even being classified as point-like sources according to their stellarity index. After discarding sources classified as QSOs, a total of 17 sources turned out to exhibit EW 0 ≥ 300 Å in at least one emission line, thus constituting our final list of EELGs. Our counts are fairly consistent with those of other samples of EELGs in the literature, although there are some differences, which were expected due to biases resulting from different selection criteria.

59 BASIC BIOLOGICAL SCIENCES↗
NASA NTRS1998

Radio Sources in Galaxy Clusters at 28.5 GHz

We present serendipitous observations of radio sources at 28.5 GHz (1 cm), which resulted from our program to image thermal Sunyaev-Zeldovich (SZ) effect in 56 galaxy clusters. In a total area of about 0.8 degrees sq., we find 64 radio sources with fluxes down to - 0.4 mJy (> 4sigma,), and within 250" from the pointing centers. The spectral indices (S varies as v(sup -alpha) of 54 sources with published low frequency flux densities range from -0.6 approximately < alpha and alpha approximately < 2 with a mean of 0.77 +/- 0.06, and a median of 0.84. Extending low frequency surveys of radio sources towards galaxy clusters CL 0016+16, Abell 665, and Abell 2218 to 28.5 GHz, and selecting sources with S(sub l.4GHz) >/= 7 mJy to form an unbiased sample, we find a mean spectral index of 0.71 +/- 0.08 and a median of 0.71. We find 4 to 7 times more sources predicted from a low frequency survey in areas without galaxy clusters. This excess cannot be accounted for by gravitational lensing of a background radio population by cluster potentials, indicating most of the detected sources are associated with galaxy clusters. The differential source count slope, gamma is approximately 1.96 (dN/dS varies as S(exp -gamma)), is flatter than what is expected for a nonevolving Euclidean population (gamma = 2.5). For the cluster Abell 2218, the presence of unsubtracted radio sources with S(sub 28.5GHz) is approximately < 0.5 mJy (- 5 sigma), can only contribute to temperature fluctuations at a level of DeltaT is approximately 10 to 25 microK. The corresponding error due to radio point source contamination in the Hubble constant derived through a combined analysis of 28.5 GHz SZ images and X-ray emission observations ranges from 1% to 6%.

Cooray, Asantha R.↗
NASA NTRS2010

Herschel-ATLAS: The Angular Correlation Function of Submillimetre Galaxies at High and Low Redshift

We present measurements of the angular correlation function of galaxies selected from the first field of the H-ATLAS survey. Careful removal of the background from galactic cirrus is essential, and currently dominates the uncertainty in our measurements. For our 250 micrometer-selected sample we detect no significant clustering, consistent with the expectation that the 250 pm-selected sources are mostly normal galaxies at z < or equal to 1. For our 350 micrometer and 500 micrometer-selected samples we detect relatively strong clustering with correlation amplitudes A of 0.2 and 1.2 at 1', but with relatively large uncertainties. For samples which preferentially select high redshift galaxies at z approx. 2-3 we detect significant strong clustering, leading to an estimate of r(0) approx. 7-11/h Mpc. The slope of our clustering measurements is very steep. delta approx. 2. The measurements are consistent with the idea that sub-mm sources consist of a low redshift population of normal galaxies and a high redshift population of highly clustered star-bursting galaxies.

Maddox, S. J.↗
NASA NTRS2011

The LBA Calibrator Survey of Southern Compact Extragalactic Radio Sources - LCS1

We present a catalogue of accurate positions and correlated flux densities for 410 flat-spectrum, compact extragalactic radio sources previously detected in the Australia Telescope 20 GHz (AT20G) survey. The catalogue spans the declination range [-90deg, -40deg] and was constructed from four 24-h very long baseline interferometry (VLBI) observing sessions with the Australian Long Baseline Array at 8.3 GHz. The VLBI detection rate in these experiments is 97 per cent, the median uncertainty of the source positions is 2.6 mas and the median correlated flux density on projected baselines longer than 1000 km is 0.14 Jy. The goals of this work are (1) to provide a pool of southern sources with positions accurate to a few milliarcsec, which can be used for phase-referencing observations, geodetic VLBI and space navigation; (2) to extend the complete flux-limited sample of compact extragalactic sources to the Southern hemisphere; and (3) to investigate the parsec-scale properties of high-frequency selected sources from the AT20G survey. As a result of this VLBI campaign, the number of compact radio sources south of declination -40deg which have measured VLBI correlated flux densities and positions known to milliarcsec accuracy has increased by a factor of 3.5.

Petrov, Leonid↗
DOE OSTI2023

Polarization and variability of compact sources measured in Planck time-ordered data

This paper introduces a new Planck Catalog of Polarized and Variable Compact Sources (PCCS-PV) comprising 153 sources, the majority of which are extragalactic. The data include both the total flux density and linear polarization measured by Planck with frequency coverage from 30 to 353 GHz, and temporal spacing ranging from days to years. We classify most sources as beamed, extragalactic radio sources; the catalog also includes several radio galaxies, Seyfert galaxies, and Galactic and Magellanic Cloud sources, including H II regions and planetary nebulae. An advanced extraction method applied directly to the multifrequency Planck time-ordered data, rather than the mission sky maps, was developed to allow an assessment of the variability of polarized sources. Our analysis of the time-ordered data from the Planck mission, tod2flux, allowed us to catalog the time-varying emission and polarization properties for these sources at the full range of polarized frequencies employed by Planck, 30-353 GHz. PCCS-PV provides the time-and frequency-dependent, polarized flux densities for all 153 sources. To illustrate some potential applications of the PCCS-PV, we conducted preliminary comparisons of our measurements of selected sources with published data from other astronomical instruments. In summary, we find general agreement between the Planck and the Institut de Radioastronomie Millimétrique (IRAM) polarization measurements as well as with the Metsähovi 37 GHz values at closely similar epochs. Here, these combined measurements also show the value of PCCS-PV results and the PCCS2 catalog for filling in missing spectral (or temporal) coverage and helping to define the spectral energy distributions of extragalactic sources. In turn, these results provide useful clues as to the physical properties of the sources.

79 ASTRONOMY AND ASTROPHYSICS↗