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At least 703 records · Page 39
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NASA NTRS1994

Relative elemental abundance and heating constraints determined for the solar corona from SERTS measurements

Intensities of EUV spectral lines were measured as a function of radius off the solar limb by two flights of Goddard's Solar EUV Rocket Telescope and Spectrograph (SERTS) for three quiet sun regions. The density scale height, line-ratio densities, line-ratio temperatures, and emission measures were determined. The line-ratio temperature determined from the ionization balances of Arnaud and Rothenflug (1985) were more self-consistent than the line-ratio temperatures obtained from the values of Arnaud and Raymond (1992). Limits on the filling factor were determined from the emission measure and the line-ratio densities for all three regions. The relative abundances of silicon, aluminum, and chromium to iron were determined. Results did agree with standard coronal relative elemental abundances for one observation, but did not agree for another. Aluminum was overabundant while silicon was underabundant. Heating was required above 1.15 solar radii for all three regions studied. For two regions, local nonconductive heating is needed for any filling factor, and in all three regions for filling factor of 0.1.

Falconer, David A.↗
NASA NTRS1994

Mantle rare gas relative abundances in a steady-state mass transport model

A model for He and Xe was presented previously which incorporates mass transfer of rare gases from an undegassed lower mantle (P) and the atmosphere into a degassed upper mantle (D). We extend the model to include Ne and Ar. Model constraints on rare gas relative abundances within P are derived. Discussions of terrestrial volatile acquisition have focused on the rare gas abundance pattern of the atmosphere relative to meteoritic components, and the pattern of rare gases still trapped in the Ear,th is important in identifying volatile capture and loss processes operating during Earth formation. The assumptions and principles of the model are discussed in Wasserburg and Porcelli (this volume). For P, the concentrations in P of the decay/nuclear products 4 He, 21 Ne, 40 Ar, and 136 Xe can be calculated from the concentrations of the parent elements U, Th, K, and Pu. The total concentration of the daughter element in P is proportional to the isotopic shifts in P. For Ar, ((40)Ar/(36)Ar)p - ((40)Ar/(36)Ar)o =Delta (exp 40) p= 40 Cp/(exp 36)C where(i)C(sub j) the concentration of isotope i in j. In D, isotope compositions are the result of mixing rare gases from P, decay/nuclear products generated in the upper mantle, and subducted rare gases (for Ar and Xe).

Porcelli, D.↗
NASA NTRS1995

Coronal abundances and their variation

This contract supports the investigation of elemental abundances in the solar corona, principally through analysis of high-resolution soft X-ray spectra from the Flat Crystal Spectrometer on the Solar Maximum Mission. The goals of the study are a characterization of the mean values of relative abundances of elements accessible in the FCS data, and information on the extent and circumstances of their variability. This report is a summation of the data analysis and reporting activities which occurred during the period of 15 April 1994 to 15 April 1995.

Saba, Julia L. R.↗
NASA NTRS1995

A search for interstellar CH3D: Limits to the methane abundance in Orion-KL

A search has been performed for interstellar CH3D via its J(K) = 1(0) - 0(0) transition at 230 GHz and its J(K) = 2(0) - l(0) and J(K) = 2(1) - 1(1) lines at 465 GHz using the NRAO 12 m and CSO 10 m telescopes towards Orion-KL. This search was done in conjunction with laboratory measurements of all three transitions of CH3D using mm/sub-mm direct absorption spectroscopy. The molecule was not detected down to a 3 sigma level of T(A) less than 0.05 K towards Orion, which suggests an upper limit to the CH3D column density of N less than 6 x 10(exp 18)/sq cm in the hot core region and a fractional abundance (with respect to H2) of less than 6 x 10(exp -6). These measurements suggest that the methane abundance in the Orion hot core is f less than 6 x 10-4, assuming D/H approximately 0.01. Such findings are in agreement with recent hot core chemical models, which suggest CH4/H2 approximately 10(exp -4).

Womack, Maria↗
NASA NTRS1994

Observations of enhanced sub-iron (Sc-Cr) to Iron abundance ratios in the low energy galactic cosmic rays in Spacelab-3 and their implications

The Anuradha cosmic ray experiment in Spacelab-3, flown in the orbit at 350 km with an inclination of 57 deg for about six days, was used to measure the low energy galactic cosmic ray (GCR) heavy ions using a specially designed CR-39 detector module incorporating the arrival time information of the particles. The abundances of sub-iron (Sc-Cr) and iron particles in the low energy interval of 30-300 MeV/N were determined from the measurements made in four different depths of the Cr-39 detector module of 150 layers. From these studies we obtained sub-iron (Sc-Cr) to iron abundance ratios of 0.8 to 1.2 in 30-300 MeV/N energy range. It is found that these ratios are enhanced by a factor of two as compared to interplanetary ratios of about 0.5. It is shown that the enhancement of the ratio inside the earth's magnetosphere is probably due to the degree of ionization of low energy Sc to Cr and Fe ions in the galactic cosmic rays and to the rigidity filtering effects of the geomagnetic field. Further studies are needed to understand fully the phenomena and their implications.

Biswas, S.↗
NASA NTRS1994

Molecular abundances and low-mass star formation. 1: Si- and S-bearing species toward IRAS 16293-2422

Results from millimeter and submillimeter spectral line surveys of the protobinary source Infrared Astronomical Satellite (IRAS) 16293-2422 are presented. Here we outline the abundances of silicon- and sulfur-containing species. A combination of rotation diagram and full statistical equilibrium/radiative transfer calculations is used to constrain the physical conditions toward IRAS 16293 and to construct its beam-averaged chemical composition over a 10 to 20 sec (1600 to 3200 AU) scale. The chemical complexity as judged by species such as SiO, OCS, and H2S, is intermediate between that of dark molecular clouds such as L134N and hot molecular cloud cores such as Orion KL. From the richness of the spectra compared to other young stellar objects of similar luminosity, it is clear that molecular abundances do not scale simply with mass; rather, the chemistry is a strong function of evolutionary state, i.e., age.

Blake, Geoffrey A.↗
NASA NTRS1994

Discovery and implications of very low metal abundances in NGC 1404 and NGC 4374

We present our analysis of ASCA PV phase observations of the elliptical galaxies NGC 1404 and NGC 4374 (M84). The average metallicities in the hot gas derived from the SIS spectra are exceptionally low, Z approximately 0.15 solar, while the temperatures are 'typical,' kT approximately 0.75 keV. We also place upper limits on intrinsic column densities. The low abundances lend support to the theory of Fe enrichment of intracluster media by protogalactic Type II supernova-driven winds and raise the possibility of a fundamental connection between baryon fraction, dissipation, and abundances in elliptical galaxies.

Loewenstein, M.↗
NASA NTRS1994

Soft X-ray spectrum of BL Lacertae object AO 0235+164 as a tracer of elemental abundances at z approximately 0.5

We report the soft X-ray spectrum of BL Lac object AO 0235+164, observed with the Einstein Observatory Imaging Proportional Counter (IPC). This object (z = 0.94) has an intervening galaxy (or a protogalactic disk) at z = 0.524 present in the line of sight, producing both radio and optical absorption lines in the background BL Lac continuum. The X-ray spectrum exhibits a substantial soft X-ray cutoff, corresponding to several times that expected from our own Galaxy; we interpret that excess cutoff as due to the intervening galaxy. The comparison of the hydrogen column density inferred from the 21 cm radio data and the X-ray absorption allows, in principle, the determination of the elemental abundances in the intervening galaxy. However, the uncertainties in both the H I spin temperature and X-ray spectral parameters only loosely restrict these abundances to be 2 +/- 1 solar, which even at the lower limit appears higher than that inferred from studies of samples of optical absoprtion-line systems.

Madejski, Greg↗
NASA NTRS1994

The abundance of interstellar oxygen toward Orion: Evidence for recent infall?

We present high S/N (greater than 800) Goddard High-Resolution Spectrograph (GHRS) observations of the weak interstellar O I lambda 1356 absorption in the low-density sight lines toward iota Ori and kappa Ori. By comparing these data with observations toward more reddened stars, we find no evidence of density-dependent depletion from the gas phase for oxygen. The derived total oxygen abundance (gas plus grains) towards iota Ori and kappa Ori is consistent with stellar and nebular determinations in Orion at a level that is one-half the solar value. We speculate that the O/H abundance ratio is lower in Orion compared to the Sun because the local Milky Way has suffered a recent infall of metal-poor material, perhaps from the Magellanic Stream.

Meyer, David M.↗
NASA NTRS1993

Search for spatial variations of the H2O abundance in the lower atmosphere of Venus from NIMS-Galileo

The spectroscopic data of the Near-Infrared Mapping Spectrometer (NIMS), recorded during the Galileo flyby of Venus, are analysed to retrieve the water vapor abundance variations in the lower atmosphere of Venus at night. The 1.18 micrometer spectral window, which probes altitude levels below 20 km, is used for this purpose. Constraints on the CO2 continuum and far-wing opacity from existing ground-based high-resolution observations are included in the modelling of the NIMS spectra. The NIMS measurements can be fitted with a water vapor mixing ratio of 30 +/- 15 ppm, in agreement with analyses of ground-based nightside observations. The water vapor abundance shows no horizontal variations exceeding 20% over a wide latitude range (40 deg S, 50 deg N) on the nightside of Venus. Within the same selection of NIMS spectra, a large enhancement in the O2 fluorescence emission at 1.27 micrometer is observed at a latitude of 40 deg S, over a spatial area about 100 km wide.

Drossart, P.↗
NASA NTRS1994

Secular trend and seasonal variability of the column abundance of N2O above the Jungfraujoch station determined from IR solar spectra

Infrared solar spectra recorded at the International Scientific Station of the Jungfraujoch (3580 m altitude), Switzerland, in 1950-1951 and from 1984 to 1992 have been analyzed to determine vertical column abundances of nitrous oxide (N2O) above the station. The best fit to the relatively dense set of measurements made between 1984 and 1992 indicates a mean exponential rate of increase equal to 0.36 +/- 0.06%/yr (1 sigma) and a seasonal modulation of 7.2% peak to peak, the minimum occurring at the end of the winter and the maximum in early September. The column abundances for April of the years 1951, 1984, and 1992 were found equal to 3.49 x 10(exp 18), 3.76 x 10(exp 18), and 3.87 x 10(exp 18) molecules/sq cm, respectively; they translate into N2O concentrations at the altitude of the Jungfraujoch equal to 275, 296, and 305 parts per billion by volume. These results indicate that the exponential rate of increase for 1951-1984 was equal to 0.23 +/- 0.04%/yr (1 sigma), thus substantially lower than for the 1984-1992 time interval and that the so-called preindustrial levels of N2O pertained until 1951 with most of the increase in atmospheric N2O occurring thereafter.

Zander, R.↗
NASA NTRS1995

Evidence for the equality of the solar photospheric and coronal abundance of iron

The Fe K-alpha and K-beta X-ray lines (wavelengths 1.94 and 1.76 A) in the solar X-ray spectrum are formed by fluoroescence of photospheric iron atoms, and the ratio of the intensity of either to the He-like iron (Fe XXV) resonance line at 1.85 A is a function of the photospheric-to-coronal abundance of iron. The temperature dependence of this ratio is weak as long as the flare temperature T(sub e) greater than or approximately equal to 15 x 10(exp 6)K. Comparison of the theoretical value of this intensity ratio with observations from crystal spectrometers on Yohkoh, Solar Maximum Mission (SMM) and P78-1 are consistent with the photospheric abundance of Fe being equal to the coronal.

Phillips, K. J. H.↗
NASA NTRS1995

A tentative detection of the 183-GHz water vapor line in the martian atmosphere: Constraints upon the H2O abundance and vertical distribution

The 183-GHz water vapor line was tentatively detected on Mars in January 1991, with the IRAM 30-m millimeter antenna, under extremely dry atmospheric conditions. The measurement refers to the whole disk. The spectral line, although marginally detected, can be fit with a constant H2O mixing ratio of 1.0 x 10(exp -5), which corresponds to a water abundance of 1 pr-microns; in any case, an upper limit of 3 pr-microns is inferred. This value is comparable to the very small abundances measured by Clancy (1992) 5 weeks before our observation and seems to imply both seasonal and long-term variations in the martian water cycle.

Encrenaz, TH.↗
NASA NTRS1996

Coronal Abundances and Their Variation

This contract supported the investigation of elemental abundances in the solar corona, principally through analysis of high-resolution soft X-ray spectra from the Flat Crystal Spectrometer on NASA's Solar Maximum Mission. The goals of the study were a characterization of the mean values of relative abundances of elements accessible in the FCS data, and information on the extent and circumstances of their variability. This is the Final Report, summarizing the data analysis and reporting activities which occurred during the period of performance, June 1993 - December 1996.

Saba, Julia L. R.↗
NASA NTRS1988

Long-Term Trends in Abundance and Distribution of Manatees (Trichechus Manatus) in the Northern Banana River, Brevard County, Florida

Four aerial survey projects were conducted between 1977 and 1986 to determine the abundance, density and distribution of West Indian manatees (Trichechus manatus), in the northern Banana River, Kennedy Space Center, Florida. Manatee density and distribution within selected portions of the 78.5 sq km study area were determined. Peak numbers of manatees occurred in spring of each year. The maximum counts increased from 56 in 1978 to 297 in 1986. Manatee abundance was lowest in the winter of each year. Mean density per flight increased from 0.52 manatees/sq km in 1977-78 to 2.73/sq km in 1984-86. This increase may reflect increases in the east coast population or shifts in the population distribution. Distributional changes were observed in the study area through time, with a lower percentage of manatees occurring in industrial areas and a correspondingly higher percentage of manatees in nonindustrial areas by 1985.

Provancha, J. A.↗
NASA NTRS1996

Trace Element Abundance Measurements on Cosmic Dust Particles

The X-Ray Microprobe on beamline X-26A at the National Synchrotron Light Source (NSLS) at Brookhaven National Laboratory was used to determine the abundances of elements from Cr through Sr in individual interplanetary dust particles (IDPs) collected from the Earth's stratosphere and the Scanning Transmission X-ray Microscope (STXM) on beamline X-1A at the NSLS was used to determine the carbon abundances and spatial distributions in IDPs. In addition, modeling was performed in an attempt to associate particular types of IDPs with specific types of parent bodies, and thus to infer the chemistry, mineralogy, and structural properties of those parent bodies.

Flynn, George↗
NASA NTRS1997

Dependence of Mercurian Atmospheric Column Abundance Estimations on Surface-Reflectance Modeling

Column abundance estimates of sodium, and analogously, potassium, in Mercury's exosphere are strongly correlated to the surface reflection model used to calibrate the spectral data and the surface reflection model incorporated into the atmospheric radiative transfer solution. Depending on the surface reflection model parameters used, there can be differences in calibration factors of up to +/- 30% and differences in estimated column abundance of up to +/- 35%. Although the surface reflectance may not be used in the calibration of spacecraft measurements, the interaction between the reflected surface light and the atmospheric brightness remains important.

Domingue, Deborah L.↗