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At least 1,027 records · Page 57
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

The early-type strong emission-line supergiants of the Magellanic Clouds - A spectroscopic zoology

The results of a spectroscopic survey of 21 early-type extreme emission line supergiants of the Large and Small Magellanic Clouds using IUE and optical spectra are presented. The combined observations are discussed and the literature on each star in the sample is summarized. The classification procedures and the methods by which effective temperatures, bolometric magnitudes, and reddenings were assigned are discussed. The derived reddening values are given along with some results concerning anomalous reddening among the sample stars. The derived mass, luminosity, and radius for each star are presented, and the ultraviolet emission lines are described. Mass-loss rates are derived and discussed, and the implications of these observations for the evolution of the most massive stars in the Local Group are addressed.

Shore, S. N.↗
NASA NTRS1986

Constraints on neutron star models of gamma-burst sources from the Einstein Observatory

Six Einstein observations of five gamma-ray burst sources are presented and discussed. With one possible exception, no point source was detected in any of the observations. The data are interpreted in the framework of neutron star models for gamma bursters. Upper limits are derived for the surface temperatures of the neutron stars assumed to be responsible for the bursts. It is shown that the lack of soft X-ray emission may impose stringent constraints on accretion rates onto neutron stars.

Pizzichini, G.↗
NASA NTRS1986

Rocket ultraviolet spectroscopy of comet Halley and abundance of carbon monoxide and carbon

Two far ultraviolet observations of comet Halley made on 26 February, 1986 and 13 March, 1986 with a sounding rocket experiment are reported. The observed CO spatial profiles can be modelled by a radial outflow model for a parent molecule and suggest that the CO is produced directly from the nucleus of the comet. Using the observed O I emission profile to deduce the H2O production rate, the abundance of CO relative to H2O is found to be 20 percent + or - 5 percent for the first flight and 17 percent + or - 4 percent for the second flight, making CO the second most abundant parent molecule in the coma. The derived production rate of atomic carbon is consistent with that expected from the photodissociation of carbon monoxide.

Woods, T. N.↗
NASA NTRS1988

The very low mass triple system - G208-44AB and G208-45

The nearby (4.7 pc) system G208-44/45 is the closest known stellar triple beyond the Centaurus system. The close astrometric pair 44AB has been resolved using IR speckle interferometry in the JHK bands, yielding individual masses of 0.14 + or - 0.03 solar and 0.10 + or - 0.02 solar for A and B, respectively. The absolute K magnitudes are 8.9 and 10.0, respectively, while the distant component 45 has K = 9.1 and should therefore have a mass slightly below that of 44A. The JHK colors and spectral types are consistent with these values. These results indicate that 44B is the lowest luminosity component known in an astrometric binary and suggest that it could be substellar. Both 44AB and 45 show strong chromospheric H-alpha and Ca II emission. The system kinematics, large implied rotation rate of 44AB, and level of chromospheric activity in the side component suggest a relatively young system.

Mccarthy, D. W., Jr.↗
NASA NTRS1990

IUE observations of comet Austin (1989c1)

Observations of comet Austin (1989c1) were made using the International Ultraviolet Explorer (IUE) satellite on December 22, 1989 (preperihelion) and on nine dates between 7 and 24 May, 1990 (postperihelion). A summary of observation dates and parameters is given. The ultraviolet spectrum is characteristic of that of non-dusty comets. Some preliminary results are presented for OH and CS production rates and dust-reflected solar continuum emission based upon the long wavelength, low resolution mode spectra; photometry using the IUE Fine Error Sensor; a detection of the CO fourth positive system in the short wavelength, low dispersion spectra; and an upper limit on S2.

Budzien, S. A.↗
NASA NTRS1991

Nitrogen airglow sources - Comparison of Triton, Titan, and earth

The individual contributions of direct solar excitation, photoelectron excitation, and magnetospheric electron excitation of Triton and Titan airglow observed by the Voyager Ultraviolet Spectrometer (UVS) are quantified. The principal spectral features of Triton's airglow are shown to be consistent with precipitation of magnetospheric electrons with power dissipation about 500 million W. Solar excitation rates of the dominant N2 and N(+) emission features are factors of 2-7 weaker than magnetospheric electron excitation. On Titan, the calculated disk center and bright limb N(+) 1085 A intensities due to solar excitation agree with observed values, while the 970 A feature is mostly N21 c5 band emission. The calculated LBH intensity by photoelectrons suggests that magnetospheric electrons play a minor role in Titan's UV airglow. On earth, solar/photoelectron excitation explains the observed N(+) 1085 A and LBH intensites and accounts for only 40 percent of the N(+) 916 A intensity.

Strobel, Darrell F.↗
NASA NTRS1992

On the use of far-infrared luminosity as a star formation indicator in galaxies

By comparing the H-alpha and far-infrared (FIR) luminosities for an optically selected and magnitude-limited (m B is not greater than 14.5) sample of galaxies, a strong nonlinearity is found in the log L(H-alpha)-log L(FIR) correlation, and a systematic decrease of the L(FIR)/L(H-alpha) ratio from early- to late-type spirals. It is shown that these trends cannot be interpreted in the frame of a single-component model for the FIR emission of galaxies, with the star formation rate as the only parameter, but are consistent with a two-component model, with the cirrus fraction as the second parameter. A decreasing contribution of the cirrus component to L(FIR) toward later types, going from about 86 percent for Sa galaxies to about 3 percent for Sdm galaxies was found. If L(FIR) is to be used as a star formation indicator in galaxies, it needs to corrected, to first order, for the cirrus component, taking into account the morphological type of the galaxy.

Sauvage, Marc↗
NASA NTRS1992

Radiative lifetimes of the CN (A 2 Pi i) electronic state

Radiative lifetimes have been measured for CN (A 2 Pi i v-prime = 2...7). Ground-state radicals formed in the 193 nm photolysis of C2N2 and ClCN were excited to A 2 Pi i v-prime = 2...7 vibrational levels. The decay was monitored by following the fluorescence. Cascading effects were eliminated by working at low pressures and monitoring emission from a single vibrational band. Quenching rates and zero-pressure radiative lifetimes were obtained from Stern-Volmer plots. The lifetimes are significantly lower than previous measurements and theoretical calculations for vibrational states v-prime over 2.

Lu, Richang↗
NASA NTRS1993

Detection of H3(+) from Uranus

The detection of H3(+) in Uranus is reported. Using the CGS4 spectrometer on the UKIRT telescope, we clearly detected 11 emission features of the H3(+) fundamental vibration-rotation band between 3.89 and 4.09 microns. These features are composed primarily of lines from the Q-branch; the strongest of them is the Q(3) blend at 3.985 microns. Analysis of these features indicates a rotational temperature of 740 +/- 25 K, an ortho-H3(+) fraction of 0.51 +/- 0.03, and a disk-averaged H3(+) column abundance of 6.5 x 10 exp 10 (+/- 10 percent) molecules/sq cm. Comparison is made with Jupiter, Saturn, and Neptune. A detection of the H2 1-0 S(1) line in Uranus and an upper limit to H3(+) emission from Neptune also are reported. The rate of energy deposition into Uranus appears to be significantly higher than the rate reported during the Voyager 2 flyby in January of 1986.

Trafton, L. M.↗
NASA NTRS1993

Analysis of hydrogen H-alpha observations of the coma of Comet P/Halley

The Monte Carlo Particle Trajectory Model of Combi and Smyth (1988) is used here to analyze observations of the H-alpha coma of Comet Halley. The solar excitation mechanism for the H-alpha emissions line is described. The H2O production rates derived for the H-alpha brightness measurements are shown to be very consistent with the H2O production rates determined from other Comet Halley observations of the H, O, and OH comae. Revised H2O production rates determined from 6300 A brightness measurements are presented.

Smyth, William H.↗
NASA NTRS1993

Evolution of the symbiotic binary system AG Pegasi - The slowest classical nova eruption ever recorded

We present an analysis of new and existing photometric and spectroscopic observations of the ongoing eruption in the symbiotic star AG Pegasi, showing that this binary has evolved considerably since the turn of the century. Recent dramatic changes in both the UV continuum and the wind from the hot component allow a more detailed analysis than in previous papers. AG Peg is composed of a normal M3 giant and a hot, compact star embedded in a dense, ionized nebula. The hot component powers the activity observed in this system, including a dense wind and a photoionized region within the outer atmosphere of the red giant. The hot component contracted in radius at roughly constant luminosity from 1850 to 1985. Its bolometric luminosity declined by a factor of about 4 during the past 5 yr. Both the mass loss rate from the hot component and the emission activity decreased in step with the hot component's total luminosity, while photospheric radiation from the red giant companion remained essentially constant.

Kenyon, Scott J.↗
NASA NTRS1994

The PSR 1800-21/G8.7-0.1 association: A view from ROSAT

We present the first imaging X-ray observation of the W30 complex which contains the Galactic SNR G8.7-0.1 and the young radio pulsar PSR 1800-21 as well as a number of discrete ultracompact H II regions. The pulsar PSR 1800-21 is detected as a count rate of 1.5 +/- 0.5/ks and diffuse emission from the northern extent of G8.7-0.1 observed. The data support an association of G8.7-0.1 and PSR 1800-21, and the peculiar morphology can be explained if the supernova which gave birth to PSR 1800-21 occurred within, or very near, a molecular cloud. The suggested scenario removes the requirement of a large transverse velocity for the pulsar, one of the greatest dificulties with the association.

Finley, John P.↗
NASA NTRS2000

Chandra Observations of Hydra A

We present Chandra X-ray Observations of the Hydra A cluster of galaxies, and we report the discovery of structure in the central 80 kpc of the cluster's X-ray-emitting gas. The most remarkable structures are depressions in the X-ray surface brightness, approx. 25 - 35 kpc diameter, that are coincident with Hydra A's radio lobes. The depressions are nearly devoid of X-ray-emitting gas, and there is no evidence for shock-heated gas surrounding the radio lobes. We suggest the gas within the surface brightness depressions was displaced as the radio lobes expanded subsonically, leaving cavities in the hot atmosphere. The gas temperature declines from 4 keV at 70 kpc to 3 keV in the inner 20 kpc of the brightest cluster galaxy (BCG), and the cooling time of the gas is approx. 600 Myr in the inner 10 kpc. These properties are consistent with the presence of a approx. 34 solar mass/yr cooling flow within a 70 kpc radius. Bright X-ray emission is present in the BCG surrounding a recently-accreted disk of nebular emission and young stars. The star formation rate is commensurate with the cooling rate of the hot gas within the volume of the disk, although the sink for the material that may be cooling at larger radii remains elusive.

McNamara, Brian↗
NASA NTRS1998

A Modeling Approach to Global Land Surface Monitoring with Low Resolution Satellite Imaging

The effects of changing land use/land cover on global climate and ecosystems due to greenhouse gas emissions and changing energy and nutrient exchange rates are being addressed by federal programs such as NASA's Mission to Planet Earth (MTPE) and by international efforts such as the International Geosphere-Biosphere Program (IGBP). The quantification of these effects depends on accurate estimates of the global extent of critical land cover types such as fire scars in tropical savannas and ponds in Arctic tundra. To address the requirement for accurate areal estimates, methods for producing regional to global maps with satellite imagery are being developed. The only practical way to produce maps over large regions of the globe is with data of coarse spatial resolution, such as Advanced Very High Resolution Radiometer (AVHRR) weather satellite imagery at 1.1 km resolution or European Remote-Sensing Satellite (ERS) radar imagery at 100 m resolution. The accuracy of pixel counts as areal estimates is in doubt, especially for highly fragmented cover types such as fire scars and ponds. Efforts to improve areal estimates from coarse resolution maps have involved regression of apparent area from coarse data versus that from fine resolution in sample areas, but it has proven difficult to acquire sufficient fine scale data to develop the regression. A method for computing accurate estimates from coarse resolution maps using little or no fine data is therefore needed.

Hlavka, Christine A.↗
NASA NTRS2010

Infrared Spectroscopy of Parent Volatiles in Comets: Implications for Astrobiology

Current cometary orbits provide information on their recent dynamical history. However, determining a given comet's formation region from its current dynamical state alone is complicated by radial migration in the proto-planetary disk and by dynamical interactions with the growing giant planets. Because comets reside for long periods of time in the outer Solar System, the ices contained in their nuclei (native ices) retain a relatively well-preserved footprint of when and where they formed, and this in turn can provide clues to conditions in the formation epoch. As a comet approaches the Sun, sublimation of its native ices releases parent volatiles into the coma where they can be measured spectroscopically. The past to - 15 years have seen the advent of infrared spectrometers with high sensitivity between about 2.8 and 5.0 micron, enabling a taxonomy among comets based on abundances of parent volatiles (e.g., H2O, CO, CH4, C2H6, HCN, CH30H, H2CO, NH3). Such molecules are of keen interest to Astrobiology, as they include important pre-biotic species that likely were required for the emergence of life on Earth and perhaps elsewhere. Approximately 20 comets have thus far been characterized, beginning with C/1996 82 (Hyakutake) in 1996. Molecular production rates are established through comparison of observed emission line intensities with those predicted by quantum mechanical fluorescence models. Abundances of parent volatiles (relative to H2O) vary among even the relatively small number of comets sampled, with the most volatile species (CO and CH4) displaying the largest variations. Techniques developed for measuring parent volatile abundances in comets will be discussed, as will possible implications for their formation.

DiSanti, Michael A.↗
NASA NTRS1989

An EUV spectrometer for atmospheric remote sensing

This paper describes the Berkeley EUV Airglow Rocket Spectrometer (BEARS) experiment, designed to investigate the interactions between the solar ionizing radiation and the earth's upper atmosphere. The primary objective of this experiment is the verification the feasibility of using EUV observations as a quantitative diagnostic of the terrestrial atmosphere and its plasma environment. The expected information provided by spectroscopic measurements of EUV emission will include data on the excitation mechanisms, excitation rates, and branching ratios. The BEARS experimental package consists of a high-resolution EUV airglow spectrometer, a hydrogen Lyman-alpha photometer to measure both the solar radiations and the geocoronal emissions, and a moderate-resolution solar EUV spectrometer. In a test experiment, the instruments were carried aboard a four-stage sounding rocket to a peak altitude of about 960 km and obtained airglow spectra in the 980-1060 A range and in the 1300-1360 range.

Chakrabarti, S.↗
NASA NTRS1987

Star formation in active galaxies and quasars

The observational evidence for a causal or statistical link between star formation and active galactic nuclei are reviewed. The chief difficulty is in quantitatively ascertaining the star formation rate in active galaxies: most of the readily observable manifestations of star formation superficially resemble those of an active nucleus. Careful multi-wavelength spatially-resolved observations demonstrate that many Seyfert galaxies are undergoing star formation. A survey of CO emission from Seyferts (interpreted in conjunction with IRAS data) suggests that type 2 Seyferts have unusually high rates of star formation, but type 1 Seyferts do not. Recent work also suggests that many powerful radio galaxies may be actively forming stars: radio galaxies with strong emission-lines often have blue colors and strong far-infrared emission. Determining the star formation rate in the host galaxies of quasars is especially difficult. Multicolor imaging and long-slit spectroscopy suggests that many of the host galaxies of radio-loud quasars are blue, and a cold interstellar medium has been detected in some quasar hosts.

Heckman, Timothy M.↗
DOE OSTI2020

Sensitivity Effects of High Temperature Overhead Conductors to Line Rating Variables

For traditional overhead transmission lines, the maximum allowable conductor operating temperature on ASCR, AAC, or AAAC lines for determining the static line ratings can be quite low, typically well under 100 C. At these low temperatures, the primary driver for determining static line ratings are assumptions made about the wind speed and direction and the ambient temperature. Assumptions for solar loading and emitted thermal radiation, driven by line emissivity and absorptivity, are secondary factors, and only provide small changes to the static ratings. However, when considering newer high temperature conductors such as ACSS, ACCR, ZTACIR, and ACCC® the maximum allowable conductor temperatures can be significantly higher, up to 250° C. This higher temperature shifts the importance of the emissivity assumptions of the overhead transmission line, due to the nature of the T4 dependence of the radiative heat loss compared to the T1 dependence of the convective heat loss, as well as shifting the dependency on local wind conditions. Typical assumptions in the United States for the emissivity/absorptivity of overhead transmission lines in determining the static ratings are to use a value of 0.5 for both parameters or set a value in the range of 0.7 to 0.9. Recent experimental tests at EPRI have shown that higher emissivity aging assumptions may not be valid in some regions of the US, and that actual values may be much lower (0.25-0.45) than older studies have predicted (0.8-0.9). Here, the assumptions of different US Regional Transmission Operators (RTOs) and different utilities within RTOs are examined for the static ratings for traditional lower operating temperatures up to 100° C as well as with the higher maximum temperature conductors associated with newer conductor designs at 250° C. The sensitivity of the static ratings is examined at both lower and higher temperature conductors with respect to overhead line emissivity and absorptivity, wind speed, wind direction, and solar loading, and ambient temperature. It is shown that the effects of the conductor absorptivity, solar flux and ambient temperature on the static rating are increased when the transmission line has a lower maximum conductor temperature. The effects of the conductor emissivity, wind direction and wind speed have increased effects on the static rating when the transmission line has a higher maximum conductor temperature. In addition, example weather data is used to calculate the conductor temperature with different line emissivity and absorptivity assumptions. This shows the effect of assumptions made for emissivity only has a minor impact for low temperature lines, but for high temperature transmission lines can cause a 150-200° C temperature swing.

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