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At least 1,225 records · Page 68
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

A study of coronal X-ray emission from short-period Algol binaries

A study of X-ray emission from five short-period Algol-type binaries based on observations with Advanced Satellite for Cosmology and Astrophysics (ASCA) and ROSAT is presented. We have observed RZ Cas with both satellites, and beta Per, U Cep, delta Lib, and TW Dra with ROSAT. Significant intensity variations are seen in the X-ray emission from RZ Cas, U Cep, TW Dra, and delta Lib. These variations seem unrelated to the eclipsing behavior of these systems and are probably due to either rotational modulation of compact active regions on the surfaces of the chromospherically active secondary components or to flaring activity in the systems. The spectra of all but one of the systems require the presence of at least two discrete plasma components with different temperatures (0.6 - 0.7 keV, and approximately 2 keV) and the abundances of the medium-Z elements 20% - 50% of the solar photospheric values. The high resolving power and signal-to-noise ratio of the ASCA spectra allow us to individually constrain the coronal abundances of O, Ne, Mg, Si, S, and Fe in RZ Cas. We demonstrate that, if we use the elemental abundances and temperatures obtained from the analysis of their ASCA spectra as (fixed) inputs, to fit the ROSAT PSPC spectra well requires the presence of a third component (kT approximately 0.2 - 0.3 keV) in RZ Cas and beta Per. A continuous emission measure model of the power-law type (EM(T) variesas (T/T(sub max)(sup alpha)) generally gives a poor fit to the ASCA and ROSAT data on most sources. Circumstellar or circumbinary absorbing matter seems to be present in some of these systems, as indicated by the variable total column density needed to fit their X-ray spectra.

Singh, K. P.↗
NASA NTRS1992

CELIAS: Charge, Element and Isotope Analysis System for the SOHO mission

The status and further development as well as first calibration of the CELIAS experiment on SOHO is presented. CELIAS is designed to measure the mass, ionic charge, and energy of low and high speed solar wind of suprathermal ions and of low energy flare particles. Through analysis of the elemental and isotopic abundances (the ionic charge state and velocity distributions of ions originating on the solar atmosphere), the investigation focuses on studying the plasma processes in various temporal and spatial scales in the solar chromosphere, transition zone, and corona. Additionally, the CELIAS experiment includes the Solar EUV Monitor (SEM). This unit, which consists of an EUV transmission grating spectrometer and three isolated silicon photodiodes as detectors, is described. The three mass and charge discriminating sensors based on the time of flight technique are also described.

Hovestadt, D.↗
NASA NTRS2005

Coronal Diagnostics of Intermediate Activity Star XI Boo A

The analysis of Xi Boo A proved difficult to adapt to our line-by-line approach because of the strong wings of the RGS instrumental profile, as has been detailed in earlier reports. While progress was also delayed because of problems in using SAS v4, we succeeded in the past year or so to bring the analysis to conclusion. Abundances have been derived using both EPIC and RGS data, confirming earlier EUVE findings of a mild solar-like FIP effect, though with some evidence of a turn-up in abundances of elements with higher FIP. Plasma densities appear normal for a moderately active stellar corona. Xi Boo A nicely bridges the gap between the very active stars and stars like the Sun, and it indeed does appear that these are the stars in which the solar-like FIP effects begins to change to the "inverse FIP" type of effect seen in the very active stars. Probing this divide was the main goal of the proposal. These results are in the process of being prepared for publication, though we have not decided the target journal as yet.

Drake, Jeremy↗
NASA NTRS1975

Origin and composition of heavy nuclei between 10 and 60 MeV per nucleon during interplanetary quiet times in 1968-1972

Results are reported for measurements of the relative abundances of nuclei from boron through iron in the energy range between 10 and 60 MeV/nucleon which were made with an instrument on board OGO 5 during the period of changing solar modulation from 1968 to 1971. The investigation was conducted to determine whether the heavy nuclei in this energy range were of solar or galactic origin. It is found that the relative abundances are in good agreement with the nuclear abundances of galactic cosmic rays, that the differential energy spectra of carbon and oxygen at these energies diverged from the characteristic modulated galactic spectrum, that changes in the C + N + O flux during this period underwent a temporal phase lag with respect to high-energy galactic cosmic rays, and that this phase lag was the same as that for helium nuclei of galactic origin with energies of 30 to 100 MeV/nucleon. It is concluded that the experimental evidence favors a galactic origin for the present nuclei. Some implications of the energy-spectrum results for cosmic-ray modulation theory are discussed.

Mogro-Campero, A.↗
NASA NTRS1972

Enhanced emission of iron nuclei in solar flares

A silica glass window from Apollo 12 CM and a piece of flint glass from the Surveyor 3 camera filter were examined for Fe nuclei tracks. A large difference between observed and predicted track densitites was found. At low rigidity (or energy), the solar particle Fe/He ratio is much higher than the photospheric abundance ratio, but decreases with increasing rigidity until it approaches the photospheric value at a rigidity of about 500 MV. It is felt that the low-energy Fe tracks are of solar origin. The implications that heavy nuclei can be preferentially emitted from a source of energetic particles are discussed. Other conclusions are the following: Rocks exposed on the lunar surface for 10 million yr would accumulate about 6 x 10 to the 12th power tracks/sq cm, and the rate of radiation-induced erosion is about 10 to the -9 cm/yr. The lunar soil should contain heavily irradiated small grains, some with track densities of about 10 to the 12th power/sq cm that have flaked from radiation-damaged rock surfaces and some that were irradiated while at the top of the soil layer.

Price, P. B.↗
NASA NTRS1971

The chemical composition of the photosphere and the corona

Collected photospheric and coronal abundances are presented in tables as summarized from a variety of references. A fairly complete picture of the composition of the solar photosphere for the first 92 elements is developed. Photospheric and coronal abundances are equal to within a factor of 2 (0.3 dex).

Withbroe, G. L.↗
NASA NTRS1989

Seed population for about 1 MeV per nucleon heavy ions accelerated by interplanetary shocks

Data obtained between 1977 and 1982 by the ISEE 1 and ISEE 3 satellites on the composition of heavy ions of about 1 MeV per nucleon, accelerated in interplanetary shock events which followed solar flare events, are examined. It was found that the average relative abundances for C, O, and Fe in the shock events were very close to those found for energetic ions in the solar flares, suggesting that, at these energies, the shock accelerated particles have the solar energetic particles as their seed population. This hypothesis is supported by the fact that the Fe/O ratio in the solar particle events is very strongly correlated with the Fe/O ratio in associated diffusive shock events.

Tan, L. C.↗
NASA NTRS1991

Seasonal cycle and secular trend of the total and tropospheric column abundance of ethane above the Jungfraujoch

The secular trend and the seasonal cycle of the total and the tropospheric column abundances of C2H6 over the Jungfraujoch Station (Switzerland) were deduced from infrared solar spectra recorded in 1951 and from 1984 to 1988. Results show a definite seasonal variation in the total vertical column abundance of C2H6, with a maximum of (1.43 + or - 0.03) x 10 to the 16th molecules/sq cm during March and April and a minimum in the fall; the ratio between the maximum and the minimum column abundances was found to be 1.62 + or - 0.11. The secular trend in the tropospheric burden above the Jungfraujoch was found to be (0.85 + or - 0.3) percent/yr.

Ehhalt, D. H.↗
NASA NTRS2004

Extra Solar Planetary Imaging Coronagraph and Science Requirements for the James Webb Telescope Observatory

1) Extra solar planetary imaging coronagraph. Direct detection and characterization of Jovian planets, and other gas giants, in orbit around nearby stars is a necessary precursor to Terrestrial Planet Finder 0 in order to estimate the probability of Terrestrial planets in our stellar neighborhood. Ground based indirect methods are biased towards large close in Jovian planets in solar systems unlikely io harbor Earthlike planets. Thus to estimate the relative abundances of terrestrial planets and to determine optimal observing strategies for TPF a pathfinder mission would be desired. The Extra-Solar Planetary Imaging Coronagraph (EPIC) is such a pathfinder mission. Upto 83 stellar systems are accessible with a 1.5 meter unobscured telescope and coronagraph combination located at the Earth-Sun L2 point. Incorporating radiometric and angular resolution considerations show that Jovians could be directly detected (5 sigma) in the 0.5 - 1.0 micron band outside of an inner working distance of 5/D with integration times of -10 - 100 hours per observation. The primary considerations for a planet imager are optical wavefront quality due to manufacturing, alignment, structural and thermal considerations. pointing stability and control, and manufacturability of coronagraphic masks and stops to increase the planetary-to- stellar contrast and mitigate against straylight. Previously proposed coronagraphic concepts are driven to extreme tolerances. however. we have developed and studied a mission, telescope and coronagraphic detection concept, which is achievable in the time frame of a Discovery class NASA mission. 2) Science requirements for the James Webb Space Telescope observatory. The James Webb Space Observatory (JWST) is an infrared observatory, which will be launched in 201 1 to an orbit at L2. JWST is a segmented, 18 mirror segment telescope with a diameter of 6.5 meters, and a clear aperture of 25 mA2. The telescope is designed to conduct imaging and spectroscopic observations from 0.6-27 microns. The primary mirror find and understand predicted first light objects, observe galaxies back to their earliest precursors so that we can understand their growth and evolution, unravel the birth and early evolution of stars and planetary systems, and study planetary systems and the origins of life. In this paper we discuss the science goals for JWST in the context of the performance requirements they levy on the observatory.

Clampin, Mark↗
NASA NTRS1993

Interstellar grains in primitive meteorites - Diamond, silicon carbide, and graphite

Primitive meteorites contain a few parts per million (ppm) of pristine interstellar grains that provide information on nuclear and chemical processes in stars. Their interstellar origin is proven by highly anomalous isotopic ratios, varying more than 1000-fold for elements such as C and N. Most grains isolated thus far are stable only under highly reducing conditions (C/O greater than 1), and apparently are 'stardust' formed in stellar atmospheres. Microdiamonds, of median size about 10 A, are most abundant (about 400-1800 ppm) but least understood. They contain anomalous noble gases including Xe-HL, which shows the signature of the r- and p-processes. Silicon carbide, of grain size 0.2-10 microns and abundance about 6 ppm, shows the signature of the s-process and apparently comes mainly from red giant carbon (AGB) stars of 1-3 solar masses. Some grains appear to be not less than 10 exp 9 a older than the solar system. Graphite spherules of grain size 0.8-7 microns and abundance less than 2 ppm contain highly anomalous C and noble gases, as well as large amounts of fossil Mg-26 from the decay of extinct Al-26. They seem to come from at least three sources, probably AGB stars, novae, and Wolf-Rayet stars.

Anders, Edward↗
NASA NTRS1993

Requirements for the early atmosphere of Mars from nitrogen isotope ratios

The N escape models of Fox and Dalgarno and Fox required the presence of a dense, early CO2 atmosphere to inhibit fractionation of the N isotopes N-15 and N-14. The computed photochemical escape fluxes are so large at the present that the isotope ratio measured by Viking (about 1.62x terrestrial) can be produced in about 1.5 b.y. This model was refined in several ways. It was updated to incorporate the variation of the escape fluxes with increases in the solar fluxes at earlier times according to the model of Zahnle and Walker. As expected, this exacerbates the problem with overfractionation, but not greatly. Most of the escape and fractionation of the N occurs in the last 1.5 b.y., when the solar flux was only slightly different from the present. The dense early atmosphere must persist only a bit longer in order to reproduce the measured isotope ratio. The model was also modified to take into account changes in the O mixing ratio with time in the past, assuming that the O abundance is proportional to the square root of the solar flux. Although the production rate of O from photodissociation of CO2 scales as the solar flux, the strength of the winds and other mixing processes also increases with the solar flux, resulting in possibly more effective transport of O to the lower atmosphere where it is destroyed by catalytic and three-body recombination mechanisms.

Fox, J. L.↗
NASA NTRS2014

Deep Mapping of Small Solar System Bodies with Galactic Cosmic Ray Secondary Particle Showers

Galactic cosmic rays rain steadily from all directions onto asteroids and comets. The interaction of these high-energy ions produces a cascade of secondary particles, including muons, which can penetrate the solid interiors of small solar system bodies. Muons, which are produced in abundance in Earth's atmosphere, have been used to image large structures on Earth, including the Great Pyramids and the interior of volcanoes. In this study, we demonstrate that the transmitted flux of muons is sensitive to the interior density structure of asteroids and comets, less than a few hundred meters in diameter. Muonography has the potential to fill a critical gap in our knowledge of the deep interiors of small bodies, providing information needed for planetary defense, in situ resource utilization, and planetary science. We use Monte Carlo codes (MCNPX and FLUKA), which accurately model galactic cosmic ray showers, to explore systematic variations in the production of muons in solid surfaces. Results of these calculations confirm the scaling of muon production in Earth's atmosphere to solid regolith materials, as predicted by a simple, semi-empirical model. Muons are primarily produced in the top meter of the regoliths of asteroids and comets. Their rate of production is over three orders of magnitude lower than in Earth's atmosphere and depends strongly on regolith density. In practice, the use of muonography to characterize the interiors of small solar system bodies must overcome their low rate of production and their dependence on regolith density, which can vary over the surface of asteroids and comets. We show that interior contrast can be resolved using a muon telescope (hodoscope) with about 1 sq m aperture with integration times ranging from hours to weeks. Design concepts for a practical hodoscope that could be deployed in situ or on an orbiting spacecraft, are described. Regolith density within the top meter of an asteroid can be determined from radar observations. A concept for a pilot mission that combines remote radar measurements with in situ muonography of a near-Earth asteroid is presented. Perceived challenges and next steps for the development of the concept are described.

Prettyman, T. H.↗
NASA NTRS1997

The sun at minimum activity: Results from the CELIAS experiment on SOHO

The charge element and isotope analysis system (CELIAS) experiment, designed to continuously measure the composition of the solar wind and solar suprathermal particles, is presented. Information on proton velocity, kinetic temperature, density and out-of-ecliptic flow angle is obtained. A preliminary statistical analysis of proton parameters and freeze-in temperatures, obtained during the first 18 months of the operation of the Solar and Heliospheric Observatory (SOHO), is presented. The first determinations of neon isotopic abundances with CELIAS yielded an excellent agreement with the Apollo-foil experiment. The magnesium isotopic composition in the solar wind agrees with the data acquired from earth.

Bochsler, P.↗
DOE OSTI2026

Solar-powered self-descaling seesaw extractor for lithium production from seawater

The low Li + concentration and the abundance of competing ions limit the efficiency of lithium extraction from seawater. Here, in this work, we report a solar-powered seesaw extractor (SPSE) to boost Li + adsorption while minimizing scaling caused by competing ions during photothermal evaporation. The SPSE features a sandwich architecture, with a hydrophilic adsorbent layer placed between two hydrophobic photothermal layers. The seesaw configuration enables Li + to be elevated and concentrated through evaporation to overcome sluggish adsorption kinetics, while the associated salt scaling is removed by the seesawing motion. As a demonstration, we assembled 60 SPSEs into a 3 × 20 array that achieved a 15.5-fold increase in local Li + concentration and a 69.1% improvement in Li + uptake over 120 h, with a Li + /Na + separation factor exceeding 370,000.

localized enrichment↗
NASA NTRS1993

Interplanetary meteoroid debris in LDEF metal craters

We have examined craters in Al and Au LDEF surfaces to determine the nature of meteoroid residue in the rare cases where projectile material is abundantly preserved in the crater floor. Typical craters contain only small amounts of residue and we find that less than 10 percent of the craters in Al have retained abundant residue consistent with survival of a significant fraction (greater than 20 percent) of the projectile mass. The residue-rich craters can usually be distinguished optically because their interiors are darker than ones with little or no apparent projectile debris. The character of the meteoroid debris in these craters ranges from thin glass liners, to thick vesicular glass containing unmelted mineral fragments, to debris dominated by unmelted mineral fragments. In the best cases of meteoroid survival, unmelted mineral fragments preserve both information on projectile mineralogy as well as other properties such as nuclear tracks caused by solar flare irradiation. The wide range of the observed abundance and alteration state of projectile residue is most probably due to differences in impact velocity. The crater liners are being studied to determine the composition of meteoroids reaching the Earth. The compositional types most commonly seen in the craters are: (1) chondritic (Mg, Si, S, Fe in approximately solar proportions), (2) Mg silicate. amd (3) iron sulfide. These are also the most common compositional types of extraterrestrial particle types collected in the stratosphere. The correlation between these compositions indicates that vapor fractionation was not a major process influencing residue composition in these craters. Although the biases involved with finding analyzable meteoroid debris in metal craters differ from those for extraterrestrial particles collected in and below the atmosphere, there is a common bias favoring particles with low entry velocity. For craters this is very strong and probably all of the metal craters with abundant residue were caused by asteroidal dust impacting at minimum velocities.

Brownlee, D. E.↗
NASA NTRS1981

A model for dwarf novae as progenitors of Type I supernovae

It is suggested that a Type I supernova event can be produced as a result of accretion at low rates (less than 10 to the -10th solar mass/year) onto the white dwarf component of a dwarf-nova close binary. At these low rates, diffusion of the CNO nuclei out of the accreted hydrogen envelope can occur on the accretion time scale, and nuclear burning will occur mainly by the proton-proton chain. Studies of this process show that, when the CNO abundance in the envelope is less than 0.0025 of solar, no thermonuclear flash occurs and no mass is lost. The result of the evolution is a gradually increasing layer of helium beneath the hydrogen-burning shell.

Starrfield, S.↗
NASA NTRS1992

Charge-exchange born He(+) ions in the solar wind

The effect of charge transfer between solar wind alpha-particles and hydrogen atoms of interstellar origin is revisited. Singly-charged helium ions born in the charge transfer carry important information on processes in the solar wind and the heliosphere. The velocity distribution of such He(+) ions is substantially different from that of He(+) pick-up ions due to ionization of the interstellar helium atoms. Estimates of the expected abundances of the charge-exchange born He(+) in the solar wind are presented, and the possibility of measuring this plasma component on deep space missions is discussed.

Gruntman, Michael A.↗