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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 1,009 records · Page 56
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NASA NTRS1992

TT Crateris - A long-period, double-lined dwarf nova

Time-resolved CCD photometry and spectroscopy of the dwarf nova TT Crt during quiescence are presented. The spectra reveal Balmer emission as well as absorption features of a K5-M0 secondary. The B, V, R light curves are dominated by a periodic variation of full amplitude 0.35 mag in V, which are interpreted as the ellipsoidal variation of the secondary star. The remarkably large amplitude indicates a high inclination (50-65 deg) and a massive white dwarf M greater than 0.8 solar mass. The ratio of the radial velocity semiamplitudes of the primary to the secondary is 0.5-1.4. The best period that can be determined from the observations is 438.17 minutes, with a possible alias at 445 minutes.

Szkody, Paula↗
NASA NTRS1993

Compositional and textural information from the dual inversion of visible, near and thermal infrared remotely sensed data

A technique is presented that allows extraction of compositional and textural information from visible, near and thermal infrared remotely sensed data. Using a library of both emissivity and reflectance spectra, endmember abundances and endmember thermal inertias are extracted from AVIRIS (Airborne Visible and Infrared Imaging Spectrometer) and TIMS (Thermal Infrared Mapping Spectrometer) data over Lunar Crater Volcanic Field, Nevada, using a dual inversion. The inversion technique is motivated by upcoming Mars Observer data and the need for separation of composition and texture parameters from sub pixel mixtures of bedrock and dust. The model employed offers the opportunity to extract compositional and textural information for a variety of endmembers within a given pixel. Geologic inferences concerning grain size, abundance, and source of endmembers can be made directly from the inverted data. These parameters are of direct relevance to Mars exploration, both for Mars Observer and for follow-on missions.

Brackett, Robert A.↗
NASA NTRS1994

Classical H II regions in the Magellanic Clouds. 1: Physical properties

In the first in a series of papers I present a detailed examination of the basic physical properties of a sample of classical H II regions in the Magellanic Clouds. Narrow band H alpha imaging is used to show that such objects are representative of the most common H II regions in the Clouds and that they display a wide range of morphological characteristics. Spectroscopic data show that, as a result of the low metal content, classical H II regions in the Clouds are systematically hotter than their Galactic counterparts. The data also suggest the existence of a correlation between the excitation of an H II region and its emission measure. The spectra of one object, DEM 243, indicates the presence of a low velocity shock passing through this H II region. I also discuss the characteristics of the extinction towards these objects and speculate that it arises from dust local to the H II regions themselves.

Wilcots, Eric M.↗
NASA NTRS1995

The temporal evolution of the 1-5 micron spectrum of V1974 CYGNI (Nova Cygni 1992)

We present 1-5 micrometer moderate- and high-resolution infrared spectra of the ONeMg nova V1974 (Nova Cygni 1992) obtained at multiple epochs during an approximately 500 day period after outburst. During the first 80 days, the spectra exhibited continuum emission from thermal bremsstrahlung (free-free radiation) with prominent recombination line emission from hydrogen, helium, nitrogen, and oxygen. The measurement Full Width at Half Maximum (FWHM) of these recombination lines suggests that the initial velocity of the ejecta was approximately equals 2400-3400 km/s. We estimate from the hydrogen recombination line ratios that the density of the ionized shell at this epoch was approximately equals 10(exp 9), with an effective electron temperature of approximately equals 5 x 10(exp 3) K. As the temporal evolution of the ejecta progressed, the hydrogen and helium lines diminished in intensity, and coronal lines of aluminum, calcium, magnesium, neon, and sulfur appeared by approximately day 80. The coronal line emission phase persisted for over 400 days. During this epoch, no significant dust formation occurred. We find that the ejecta of V1974 Cyg were overabundant in aluminum with respect to silicon by a factor of approximately equals 5 and in magnesium with respect to silicon by a factor of greater than or equal to 3 relative to the solar photosphere. Comparison of our observed overabundances with recent model predictions of elemental synthesis in ONeMg outbursts suggests that the accreted envelope on V1974 Cyg was close to solar composition and that the precursor ONeMg white dwarf had a mass of approximately equals 1 solar mass.

Woodward, Charles E.↗
NASA NTRS1995

Heating, ionization and upward discharges in the mesosphere due to intense quasi-electrostatic thundercloud fields

Quasi-electrostatic (QE) fields that temporarily exist at high altitudes following the sudden removal (e.g., by a lightning discharge) of thundercloud charge at low altitudes are found to significantly heat mesospheric electrons and produce ionization and light. The intensity, spatial extent, duration and spectra of optical emissions produced are consistent with the observed features of the Red Sprite type of upward discharges.

Pasko, Victor P.↗
NASA NTRS1997

Qualitative Flow Visualization of a 110-N Hydrogen/Oxygen Laboratory Model Thruster

The flow field inside a 110 N gaseous hydrogen/oxygen thruster was investigated using an optically accessible, two-dimensional laboratory test model installed in a high altitude chamber. The injector for this study produced an oxidizer-rich core flow, which was designed to fully mix and react inside a fuel-film sleeve insert before emerging into the main chamber section, where a substantial fuel film cooling layer was added to protect the chamber wall. Techniques used to investigate the flow consisted of spontaneous Raman spectra measurements, visible emission imaging, ultraviolet hydroxyl spectroscopy, and high speed schlieren imaging. Experimental results indicate that the oxygen rich core flow continued to react while emerging from the fuel-film sleeve, suggesting incomplete mixing of the hydrogen in the oxygen rich core flow. Experiments also showed that the fuel film cooling protective layer retained its integrity throughout the straight section of the combustion chamber. In the converging portion of the chamber, however, a turbulent reaction zone near the wall destroyed the integrity of the film layer, a result which implies that a lower contraction angle may improve the fuel film cooling in the converging section and extend the hardware lifetime.

deGroot, Wim A.↗
NASA NTRS2002

The Ejecta of Eta Carinae as Studied by STIS

The Space Telescope Imaging Spectrograph has been used to study the emission and absorption spectra of ejecta surrounding Eta Carinae. Discussion will be presented on the overall structure of the Homunculus, the Weigelt blobs and the Strontium filament. Three visits have been accomplished with the Position Angle precisely the same and covering the Central Source and Weigelt Blobs B and D. Deep spectra have been done at several positions to obtain the overall velocity structure of the Homunculus and the disk region. Mapping has been done with the STIS medium dispersion gratings set near H beta and H alpha. We have obtained full coverage of the strontium filament from 1640 Angstroms to 10300 Angstroms. The structure and physical properties will be described.

Gull, Theodore R.↗
NASA NTRS2004

Meteors do not break exogenous organic molecules into high yields of diatomics

Meteoroids that dominate the Earth's extraterrestrial mass influx (50-300 microm size range) may have contributed a unique blend of exogenous organic molecules at the time of the origin of life. Such meteoroids are so large that most of their mass is ablated in the Earth's atmosphere. In the process, organic molecules are decomposed and chemically altered to molecules differently from those delivered to the Earth's surface by smaller (<50 microm) micrometeorites and larger (>10 cm) meteorites. The question addressed here is whether the organic matter in these meteoroids is fully decomposed into atoms or diatomic compounds during ablation. If not, then the ablation products made available for prebiotic organic chemistry, and perhaps early biology, might have retained some memory of their astrophysical nature. To test this hypothesis we searched for CN emission in meteor spectra in an airborne experiment during the 2001 Leonid meteor storm. We found that the meteor's light-emitting air plasma, which included products of meteor ablation, contained less than 1 CN molecule for every 30 meteoric iron atoms. This contrasts sharply with the nitrogen/iron ratio of 1:1.2 in the solid matter of comet 1P/Halley. Unless the nitrogen content or the abundance of complex organic matter in the Leonid parent body, comet 55P/Tempel-Tuttle, differs from that in comet 1P/Halley, it appears that very little of that organic nitrogen decomposes into CN molecules during meteor ablation in the rarefied flow conditions that characterize the atmospheric entry of meteoroids approximately 50 microm-10 cm in size. We propose that the organics of such meteoroids survive instead as larger compounds.

Meteoroids↗
NASA NTRS2005

Martian Radiative Transfer Modeling Using the Optimal Spectral Sampling Method

The large volume of existing and planned infrared observations of Mars have prompted the development of a new martian radiative transfer model that could be used in the retrievals of atmospheric and surface properties. The model is based on the Optimal Spectral Sampling (OSS) method [1]. The method is a fast and accurate monochromatic technique applicable to a wide range of remote sensing platforms (from microwave to UV) and was originally developed for the real-time processing of infrared and microwave data acquired by instruments aboard the satellites forming part of the next-generation global weather satellite system NPOESS (National Polarorbiting Operational Satellite System) [2]. As part of our on-going research related to the radiative properties of the martian polar caps, we have begun the development of a martian OSS model with the goal of using it to perform self-consistent atmospheric corrections necessary to retrieve caps emissivity from the Thermal Emission Spectrometer (TES) spectra. While the caps will provide the initial focus area for applying the new model, it is hoped that the model will be of interest to the wider Mars remote sensing community.

Eluszkiewicz, J.↗
NASA NTRS2005

An evolving trio of hybrid stars: C111

Hybrid stars are a class of cool, luminous single stars originally identified based on the appearance of their ultraviolet IUE spectra. C IV emission is present (signifying temperatures of at least lo5 K), and asymmetric emission cores of Mg I1 are found, accompanied by absorption features at low and high velocities, indicating a massive stellar wind and circumstellar material. Many members of this class have been identified and X-rays have been detected from most hybrids. They represent the critical evolutionary state between coronal-like objects and the Alpha Ori-like objects and assume a pivotal role in the definition of coronal evolution, atmospheric heating processes, and mechanisms to drive winds of cool stars.

Sonneborn, George↗
NASA NTRS1999

Young Stars and Non-Stella Emission in the Aligned Radio Galaxy 3C 256

We present ground-based images of the z=1.824 radio galaxy 3C 256 in the standard BVRIJHK filters and an interference filter centered at 8800 A, a Hubble Space Telescope image in a filter dominated by Ly alpha emission (F336W), and spectra covering rest-frame wavelengths from Ly alpha to [O III} lambda 5007.

Radio Galaxies↗
NASA NTRS2006

Sub-millimeter Spectroscopy of Astrophysically Important Molecules and Ions: Metal Hydrides, Halides, and Cyanides

With the advent of SOFIA, Herschel, and SAFIR, new wavelength regions will become routinely accessible for astronomical spectroscopy, particularly at submm frequencies (0.5-1.1 THz). Molecular emission dominates the spectra of dense interstellar gas at these wavelengths. Because heterodyne detectors are major instruments of these missions, accurate knowledge of transition frequencies is crucial for their success. The Ziurys spectroscopy laboratory has been focusing on the measurement of the pure rotational transitions of astrophysically important molecules in the sub-mm regime. Of particular interest have been metal hydride species and their ions, as well as metal halides and cyanides. A new avenue of study has included metal bearing molecular ions.

Ziurys, L. M.↗
NASA NTRS2007

Method bacterial endospore quantification using lanthanide dipicolinate luminescence

A lanthanide is combined with a medium to be tested for endospores. The dipicolinic acid released from the endospores binds the lanthanides, which have distinctive emission (i.e., luminescence) spectra, and are detected using photoluminescence. The concentration of spores is determined by preparing a calibration curve generated from photoluminescence spectra of lanthanide complex mixed with spores of a known concentration. A lanthanide complex is used as the analysis reagent, and is comprised of lanthanide ions bound to multidentate ligands that increase the dipicolinic acid binding constant through a cooperative binding effect with respect to lanthanide chloride. The resulting combined effect of increasing the binding constant and eliminating coordinated water and multiple equilibria increase the sensitivity of the endospore assay by an estimated three to four orders of magnitude over prior art of endospore detection based on lanthanide luminescence.

Ponce, Adrian↗
NASA NTRS2008

The Radio Luminosity Function and Galaxy Evolution in the Coma Cluster

We investigate the radio luminosity function and radio source population for two fields within the Coma cluster of galaxies, with the fields centered on the cluster core and southwest infall region and each covering about half a square degree. Using VLA data with a typical rms sensitivity of 28 (mu)Jy per 4.4" beam, we identify 249 radio sources with optical counterparts brighter than r = 22 (equivalent to M(sub r) = -13 for cluster member galaxies). Comprehensive optical spectroscopy identifies 38 of these as members of the Coma cluster, evenly split between sources powered by an active nucleus and sources powered by active star formation. The radio-detected star-forming galaxies are restricted to radio luminosities between about 10(exp 21) and 10(exp 22) W/Hz, an interesting result given that star formation dominates field radio luminosity functions below about 10(exp 23) W/Hz. The majority of the radio-detected star-forming galaxies have characteristics of starbursts, including high specific star formation rates and optical spectra with strong emission lines. In conjunction with prior studies on post-starburst galaxies within the Coma cluster, this is consistent with a picture in which late-type galaxies entering Coma undergo a starburst prior to a rapid cessation of star formation. Optically bright elliptical galaxies (Mr less than or equals -20.5) make the largest contribution to the radio luminosity function at both the high (> approx. 3x10(exp 22) W/Hz) and low (< approx. 10(exp 21) W/Hz) ends. Through a stacking analysis of these optically-bright ellipticals we find that they continue to harbor radio sources down to luminosities as faint as 3x10(exp 19) W/Hz. However, contrary to published results for the Virgo cluster we find no evidence for the existence of a population of optically faint (M(sub r) approx. equals -14) dwarf ellipticals hosting strong radio AGN.

Miller, Neal A.↗
NASA NTRS2010

Spitzer Observations of Dust Destruction in the Puppis A Supernova Remnant

Imaging and spectral observations of the Puppis A supernova remnant (SNR) with the Spitzer Space Telescope confirm that its IR emission is dominated by the thermal continuum emission of swept-up interstellar dust which is collisionally heated by the X-ray emitting gas of the SNR. Line emission is too weak to affect the fluxes measured in broadband observations, and is poorly correlated with the IR or X-ray emission. Modeling of spectra from regions both in the SNR and in the associated ISM show that the ubiquitous polycyclic aromatic hydrocarbons (PAHs) of the ISM are destroyed within the SNR, along with nearly 25% of the mass of graphite and silicate dust grains.

Arendt, Richard G.↗
NASA NTRS2014

The Lunar Atmosphere and Dust Environment Explorer (LADEE): Initial Science Results

On September 6, 2013, a near-perfect launch of the first Minotaur V rocket successfully carried NASA's Lunar Atmosphere and Dust Environment Explorer (LADEE) into a high-eccentricity geocentric orbit. LADEE arrived at the Moon on October 6, 2013, dur-ing the government shutdown. The spacecraft impact-ed the lunar surface on April 18, 2014, following a completely successful mission. LADEE's science objectives were twofold: (1) De-termine the composition and variability of the lunar atmosphere; (2) Characterize the lunar exospheric dust environment, and its variability. The LADEE science payload consisted of the Lunar Dust Experiment (LDEX), which sensed dust impacts in situ, for parti-cles between 100 nm and 5 micrometers; a neutral mass spectrometer (NMS), which sampled lunar exo-spheric gases in situ, over the 2-150 Dalton mass range; an ultraviolet/visible spectrometer (UVS) ac-quired spectra of atmospheric emissions and scattered light from tenuous dust, spanning a 250-800 nm wave-length range. UVS also performed dust extinction measurements via a separate solar viewer optic. The following are preliminary results for the lunar exosphere: (1) The helium exosphere of the Moon, first observed during Apollo, is clearly dominated by the delivery of solar wind He++. (2) Neon 20 is clearly seen as an important constituent of the exosphere. (3) Argon 40, also observed during Apollo and arising from interior outgassing, exhibits variations related to surface temperature-driven condensation and release, and is also enhanced over specific selenographic longi-tudes. (4) The sodium abundance varies with both lu-nar phase and with meteoroid influx, implicating both solar wind sputtering and impact vaporization process-es. (5) Potassium was also routinely monitored and exhibits some of the same properties as sodium. (6) Other candidate species were seen by both NMS and UVS, and await confirmation. Dust measurements have revealed a persistent "shroud" of small dust particles between 0.7 and sev-eral micrometers in size, present over the pre-dawn and morning sector of the Moon. This tenuous dust exosphere, with densities of approximately 10(exp -5) m(exp -3), appears to be sustained by the ejecta of micrometeoroid impacts.

lunar atmosphere↗
NASA NTRS2014

Extreme Blazars Studied with Fermi-Lat and Suzaku: 1ES 0347-121 and Blazar Candidate HESS J1943+213

We report on our study of high-energy properties of two peculiar TeV emitters: the "extreme blazar" 1ES 0347-121 and the "extreme blazar candidate" HESS J1943+213 located near the Galactic plane. Both objects are characterized by quiescent synchrotron emission with flat spectra extending up to the hard X-ray range, and both were reported to be missing GeV (gigaelectronvolt) counterparts in the Fermi Large Area Telescope (LAT) two-year Source Catalog. We analyze a 4.5 year accumulation of the Fermi-LAT data, resulting in the detection of 1ES 0347-121 in the GeV band, as well as in improved upper limits for HESS J1943+213. We also present the analysis results of newly acquired Suzaku data for HESS J1943+213. The X-ray spectrum is well represented by a single power law extending up to 25 keV (kiloelectronvolts) with photon index 2.00 plus or minus 0.02 and a moderate absorption in excess of the Galactic value, which is in agreement with previous X-ray observations. No short-term X-ray variability was found over the 80 kilosecond duration of the Suzaku exposure. Under the blazar hypothesis, we modeled the spectral energy distributions of 1ES 0347-121 and HESS J1943+213, and we derived constraints on the intergalactic magnetic field strength and source energetics. We conclude that although the classification of HESS J1943+213 has not yet been determined, the blazar hypothesis remains the most plausible option since, in particular, the broadband spectra of the two analyzed sources along with the source model parameters closely resemble each other, and the newly available Wide-field Infrared Survey Explorer (WISE) and UKIRT (United Kingdom Infrared Telescope) Infrared Deep Sky Survey data for HESS J1943+213 are consistent with the presence of an elliptical host at the distance of approximately 600 Mpc (megaparsecs).

blazar↗
NASA NTRS2005

Stellar Activity and Mass Loss from A and F Supergiants

This grant supported the observing and data analysis for FUSE Cycle 4 project DO47 to observe five late-A and F supergiants using a total observing allocation of 150 ksec. Stellar activity on A and F supergiants has been poorly studied in the past; primarily because the photospheric continuum dominates any chromospheric (~ 10 4 K) or transition region (TR; ~ 10 5 K) emission lines far into the ultraviolet. FUSE observations of A and F supergiants offer one of the best methods to study stellar activity on these stars, because many activity indicators longward of 1200 A are swamped by the photospheric continuum emission. We used FUSE FUV spectra to search for 0 VI and C I11 TR emission lines and obtained data for t Car (A8 Ib, for 60.5 ksec, on 2003 Apr 27), 8 Sco (F1 11, 22.7 ksec, 2003 Aug 2), ct Per (F5 Ib, 30.8 ksec, 2003 Oct l), a UMi (F7 Ib-11, 23.9 ksec, 2003 Oct 14), and y Cyg (F8 Ib, 25.8 ksec, 2003 Oct 18). These observations used the large LWRS aperture and collected data in time-tagged mode. The LWRS aperture is large enough that the target should remain within the aperture with the normal level of FUSE pointing jitter and target drift. We examined the stellar signal and found that the targets were well within the aperture throughout the observation. The data were split into night-time and day-time data so that the effects of airglow emission were recognizable, and combined day and night spectra were generated using CALFUSE 2.4.0 .

Brown, Alexander↗