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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 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

The CatWISE Preliminary Catalog: Motions from WISE and NEOWISE Data

CatWISE is a program to catalog sources selected from combined WISE and NEOWISE all-sky survey data at 3.4 and 4.6 μm (W1 and W2). The CatWISE Preliminary Catalog consists of 900,849,014 sources measured in data collected from 2010 to 2016. This data set represents four times as many exposures and spans over 10 times as large a time baseline as that used for the AllWISE Catalog. CatWISE adapts AllWISE software to measure the sources in coadded images created from six-month subsets of these data, each representing one coverage of the inertial sky, or epoch. The catalog includes the measured motion of sources in eight epochs over the 6.5 yr span of the data. From comparison to Spitzer, signal-to-noise ratio = 5 limits in magnitudes in the Vega system are W1 = 17.67 and W2 = 16.47, compared to W1 = 16.96 and W2 = 16.02 for AllWISE. From comparison to Gaia, CatWISE positions have typical accuracies of 50 mas for stars at W1 = 10 mag and 275 mas for stars at W1 = 15.5 mag. Proper motions have typical accuracies of 10 mas yr -1 and 30 mas yr -1 for stars with these brightnesses, an order of magnitude better than from AllWISE. The catalog is available in the WISE/NEOWISE Enhanced and Contributed Products area of the NASA/IPAC Infrared Science Archive.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

The Dark Energy Survey Data Release 2

In this work, we present the second public data release of the Dark Energy Survey, DES DR2, based on optical/near-infrared imaging by the Dark Energy Camera mounted on the 4 m Blanco telescope at Cerro Tololo Inter-American Observatory in Chile. DES DR2 consists of reduced single-epoch and coadded images, a source catalog derived from coadded images, and associated data products assembled from 6 yr of DES science operations. This release includes data from the DES wide-area survey covering ~5000 deg 2 of the southern Galactic cap in five broad photometric bands, grizY. DES DR2 has a median delivered point-spread function FWHM of g = 1.11'', r = 0.95'', i = 0.88'', z = 0.83'', and Y = 0farcs90, photometric uniformity with a standard deviation of < 3 mmag with respect to Gaia DR2 G band, a photometric accuracy of ~11 mmag, and a median internal astrometric precision of ~27 mas. The median coadded catalog depth for a 1farcs95 diameter aperture at signal-to-noise ratio = 10 is g = 24.7, r = 24.4, i = 23.8, z = 23.1, and Y = 21.7 mag. DES DR2 includes ~691 million distinct astronomical objects detected in 10,169 coadded image tiles of size 0.534 deg2 produced from 76,217 single-epoch images. After a basic quality selection, benchmark galaxy and stellar samples contain 543 million and 145 million objects, respectively. These data are accessible through several interfaces, including interactive image visualization tools, web-based query clients, image cutout servers, and Jupyter notebooks. DES DR2 constitutes the largest photometric data set to date at the achieved depth and photometric precision.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Finding Peas in the Early Universe with JWST

The Early Release Observations (EROs) of JWST beautifully demonstrate the promise of JWST in characterizing the universe at Cosmic Dawn. We analyze the Near Infrared Spectrograph ERO spectra of three z ~ 8 galaxies to determine their metallicities, gas temperatures, and ionization. These galaxies offer the first opportunity to understand the physical properties of Epoch-of-Reionization galaxies through detailed rest-optical emission-line spectroscopy. We show that these objects have metal abundances $12+\mathrm{log}[{\rm{O}}/{\rm{H}}]\,\approx$ 6.9–8.3, based on both the T e method and on a recent calibration of the R 23 metallicity indicator. Since the spectra are some of the earliest science data from JWST, we compare several line ratios with values expected from robust physics, to validate our measurement procedures. We compare the abundances and emission-line ratios to a nearby sample of Green Pea galaxies—a population of nearby emission-line galaxies whose UV properties resemble Epoch-of-Reionization galaxies, and which often have large Lyman continuum escape fractions. The JWST data show striking further similarities between these high-redshift galaxies and nearby Green Peas. The z ~ 8 galaxies span the metallicity range covered by Green Peas. They also show the compact morphology that is typical of emission-line-dominated galaxies at all redshifts. Based on these similarities with Green Peas, it is likely that these are the first rest-optical spectra of galaxies that are actively driving cosmological reionization.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2025

Spotting Stasis in Cosmological Perturbations.

An analysis of the unique properties of the growth of cosmological perturbations during a stasis epoch in the early universe, and how these properties may provide a signature for the discovery of such an epoch.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2025

The DESI Y1 RR Lyrae catalog I: Empirical modeling of the cyclic variation of spectroscopic properties and a chemodynamical analysis of the outer halo

We present the catalog of RR Lyrae stars observed in the first year of operations of the Dark Energy Spectroscopic Instrument (DESI) survey. This catalog contains 6,240 RR Lyrae stars out to $\sim100$ kpc from the Galactic center and over 12,000 individual epochs with homogeneously-derived stellar atmospheric parameters. We introduce a novel methodology to model the cyclical variation of the spectroscopic properties of RR Lyrae from single-epoch measurements. We employ this method to infer the radial velocity and effective temperature variation of fundamental mode and first-overtone RR Lyrae stars and to determine their systemic velocities and mean temperatures. For fundamental mode pulsators, we obtain radial velocity curves with amplitudes of $\sim$30--50 km s$^{-1}$ and effective temperature curves with 300--1,000 K variations, whereas for first-overtone pulsators these amplitudes are $\sim20$ km s$^{-1}$ and $\sim 600$ K, respectively. We use our sample to study the metallicity distribution of the halo and its dependence on Galactocentric distance ($R_{\rm GC}$). Using a radius-dependent mixture model, we split the data into chemodynamically distinct components and find that our inner halo sample ($R_{\rm GC}\lesssim50$ kpc) is predominantly composed of stars with [Fe/H] $\sim-1.5$ dex and largely radial orbits (with an anisotropy parameter $\beta\sim0.94$), that we associate with the Gaia-Sausage-Enceladus merger event. Stars in the outer halo field exhibit a broader and more metal-poor [Fe/H] distribution with more circular orbits ($\beta\sim0.39$). The metallicity gradient of the metal-rich and the metal-poor components is found to be $0.005$ and $0.010$ dex kpc$^{-1}$, respectively. Our catalog highlights DESI's tantalizing potential for studying the Milky Way and the pulsation properties of RR Lyrae stars in the era of large spectroscopic surveys.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2026

Statistical and temporal characteristics of sawtooth events

Magnetospheric sawtooth events are characterized by periodic particle injections and magnetic dipolarizations spread quasi-simultaneously across a wide range of magnetic local times. We present a comprehensive statistical study of magnetospheric sawtooth events (STEs) during solar cycle 24 (2008–2016), extending previous catalogs and enabling solar cycle comparisons. Our results confirm that STEs predominantly occur during the rising and declining phases of the solar cycle, and are strongly associated with geomagnetic storms. Superposed epoch analysis reveals near-simultaneous particle injections across all magnetic local time sectors, but magnetic field dipolarization confined to the midnight region. These results support a scenario in which nightside tail reconnection and enhanced convection are the primary drivers of sawtooth oscillations. The localization of magnetic dipolarizations during STEs challenges global instability interpretations and suggests that STEs represent a stormtime substorm mode triggered under specific solar wind and magnetotail conditions. Superposed epoch analyses also show enhanced oxygen content in the magnetosphere during sawtooth events, but do not show a significant difference from geomagnetic storms that do not exhibit periodic behavior.

58 GEOSCIENCES↗
NASA NTRS1971

The AGK3, a basis for a general (northern) reference catalogue of positions and proper motions

The original concept of the international AGK3 program is presented and a report on the methods applied and on the progress of the work is given. The results in the form of revised positions of the AGK2 reduced to the FK4 system, and of AGK3, can be extrapolated easily to earlier epochs, as far back as those of AGK1, and the mean error for these epochs will permit one the deriving of reliable values for systematic corrections of the old catalogs. By using the AGK2/3 positions a general catalog of roughly to the ninth magnitude can be constructed by including large catalogs such as AGK1, AC, and Yale. Thus a new edition of the type of the SAO catalog for the northern hemisphere can be produced.

Dieckvoss, W.↗
NASA NTRS1972

Some recent observations and interpretation of the Jupiter decimeter emission

The decimetric emission consists partly of thermal radiation from the planetary disk and partly of nonthermal radiation from a region of larger angular extent and is thought to result from synchrotron emission by relativistic electrons in the magnetic field. Four topics relating to the decimetric emission are discussed. (1) A comparison is made of maps giving detailed brightness contours. One was obtained for epoch 1963.8 and was at a wavelength of 10.4 cm. The second was for epoch 1967.2 at 21.3 cm. (2) Interferometric data at 21.1 cm taken in April 1968 and May 1979 indicate that the emission centroid is fixed in Jupiter and rotates with it. (3) Circular polarization observations are described and are used to obtain a surface magnetic field strength at the equator between 3.2 and 15.2 gauss. (4) An upper limit on the Faraday rotation is used to set an upper limit on the density of thermal electrons surrounding Jupiter, and uncertainties in the results are discussed.

Berge, G. L.↗
NASA NTRS1973

System description and operating guide for DSAS illumination and moon conflict programs

The DSAS Illumination and Moon Conflict programs are described which during an orbit when the DSAS (Digital Solar Aspect Sensor) will record the direct rays of the sun, and the periods of time when the horizon scanners will come in conflict with the moon. The DSAS Illumination Program makes use of an orbit tape (or epoch time and orbital elements) in addition to an ephemeris tape containing positions of the sun and moon. The Moon Conflict Program makes use of the same ephemeris tape with sun and moon positions, but uses only epoch time and orbital elements for the satellite positions. These programs were designed for the TIROS or ITOS series spacecraft but may be utilized by any spacecraft with similar sensors.

Dunker, S. C.↗
NASA NTRS1972

Omega VLF timing revision 1

The report specifically discusses time dissemination techniques, including epoch determination, frequency determination, and ambiguity resolution. It also discusses operational considerations including equipment, path selection, and adjustment procedure. epoch (the actual location or timing of periodic events) is shown to be both maintainable and calibratable by the techniques described to better than 3-microsecond accuracy; and frequency (the uniformity of the time scale) to about one part in 10 to the 12th power.

Swanson, E. R.↗
NASA NTRS1973

Climatic change on Mars.

It is pointed out that Mars is the only known planet with a major atmospheric constituent condensable at typical surface temperatures. The temperatures range from 290 K at equatorial noon to a temperature at the cold pole of 145 K in polar winter. There may be three different periods of climatic variation on Mars. Aspects of reversible climatic instability might possibly explain the channels and other features suggestive of the extensive occurrence of liquid water on Mars. An aqueous epoch on Mars would have important biological and other geological implications. Putative Martian organisms which flourish in the aqueous epoch may now be in cryptobiotic repose.

Sagan, C.↗
NASA NTRS1972

GEODYN programmer's guide, volume 2, part 2

A computer program for executive control routine for orbit integration of artificial satellites is presented. At the beginning of each arc, the program initiates required constants as well as the variational partials at epoch. If epoch needs to be reset to a previous time, the program negates the stepsize, and calls for integration backward to the desired time. After backward integration is completed, the program resets the stepsize to the proper positive quantity.

Mullins, N. E.↗
NASA NTRS1975

Some properties of the Svalgaard A/C index

Several properties of the A/C index of polar cap variations introduced by L. Svalgaard in 1972 have been found to vary with time. In the presatellite era, C days, as measured by the Ap index, are almost twice as geomagnetically active as A days, while in the modern epoch they have essentially identical activity. Prior to 1962 there were over 40% more A days than C days per year, while during the modern epoch there are essentially equal numbers of A days and C days. In view of this strong bias to assigning a 'toward' classification on geomagnetically active days it is recommended that the Svalgaard A/C classification not be used in studies of geomagnetic activity. It is also recommended that a full and thorough documentation of the index be prepared and/or that others undertake to compile such a classification separately.

Russell, C. T.↗
NASA NTRS1976

Apparent 'superrelativistic' expansion of the extragalactic radio source 3C 345

The compact extragalactic radio source 3C 345 was observed by very-long-baseline interferometry (wavelength about 3.8 cm) at 12 epochs distributed over the nearly four-year period from February 1971 to October 1974. For one of these epochs, the multibaseline data were sufficient to allow the brightness distribution to be estimated in a model-independent manner; the resultant distribution was clearly dominated by two components. The remaining sets of data were also represented adequately by two-component models. The angular separation of the two components increased during this period from about 1.00 to 1.30 milliarcsec, corresponding to an apparent average speed of expansion of approximately 2.5 c at a fixed position angle of 105 (plus or minus 5) deg. These results, coupled with the fact that contraction has never been observed, seem difficult to reconcile with the so-called Christmas-tree model of the 'superrelativistic' expansion of extragalactic radio sources.

Wittels, J. J.↗
NASA NTRS1977

Interpretation of observed cosmic microwave background radiation

It is argued that the 'surface of last scattering' of the observed microwave background radiation corresponds to the distribution of dust in galaxies or protogalaxies with a temperature of about 110 K at the epoch corresponding to Z roughly equal to 40. This is in contrast with the plasma temperature of over 3,000 K at an earlier epoch (Z greater than about 1,000), as given by the canonical model of big bang cosmologies. In view of this, the claim that the microwave background radiation lends strong support to hot big bang cosmologies is without foundation.

Alfven, H.↗
NASA NTRS1977

Orbit determination accuracies using satellite-to-satellite tracking

The uncertainty in relay satellite sate is a significant error source which cannot be ignored in the reduction of satellite-to-satellite tracking data. Based on simulations and real data reductions, it is numerically impractical to use simultaneous unconstrained solutions to determine both relay and user satellite epoch states. A Bayesian or least squares estimation technique with an a priori procedure is presented which permits the adjustment of relay satellite epoch state in the reduction of satellite-to-satellite tracking data without the numerical difficulties introduced by an ill-conditioned normal matrix.

Vonbun, F. O.↗
NASA NTRS1978

Solar plages and the vorticity of the earth's atmosphere

Three superimposed epoch analyses of the vorticity area index (VAI) at 500 mbar are described. The analyses used the following definitions of the zero days: (1) the central meridian passage (CMP) of very active solar plages; (2) the occurrence of peak values of the 10.7 cm solar radio flux; and (3) the CMP of active solar plages also accompanied at CMP by sharp rises in 10.7 cm solar radio noise. All three superimposed epoch analyses show a sustained rise in VAI several days before the zero day; the rise continues through the zero day and is followed by a sustained minimum in VAI several days after the zero day. The results suggest that the location of the very active plages play an important role in determining their meteorological influence. It is possible that the initial rise in VAI is caused by enhanced electromagnetic radiation associated with the solar activity, and that the decrease some days later is the result of the geomagnetic storm particle emission that generally follows the zero date.

Olson, R. H.↗
NASA NTRS1978

Geophysical and geochemical evolution of the lunar magma ocean

There is increasing evidence that at least the outer few hundred kilometers of the moon were melted immediately following accretion. This paper studies the evolution of this lunar magma ocean. The long time scale for solidification leads to the inference that the plagioclase-rich (ANT) lunar crust began forming, perhaps preceded by local accumulations termed 'rockbergs', at the very beginning of the magma ocean epoch. In this view the cooling and solidification of the magma ocean was primarily controlled by the rate at which heat could be conducted across the floating ANT crust. Thus the thickness of the crust was the factor controlling the lunar solidification time. Heat arising from enthalpy of crystallization was transported in the magma by convection. Mixing length theory is used to deduce the principal flow velocity (typically several cm/s) during convection. The magma ocean is deduced to have been turbulent down to a characteristic length scale of the order of 100 m, and to have overturned on a time scale of the order of 1 yr for most of the magma ocean epoch.

Herbert, F.↗