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  • ASTROPHYSICS  (16,581)
  • 1
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    In:  CASI
    Publication Date: 2019-06-28
    Description: NASA/GRO grant NAG 5-2081, at the University of Chicago, has provided support for a broad program of theoretical research in nuclear astrophysics and related areas, with regard to gamma-ray and hard X-ray emission from classical nova explosions. This research emphasized the possible detection of 22Na gamma-ray line emission from nearby novae involving ONeMg white dwarfs, the detailed examination of 26Al production in novae, and the possible detection of the predicted early gamma ray emission from novae that arises from the decay of the short lived, positron emitting isotopes of CNO elements. Studies of nova related problems have consumed an increasing fraction of the Principal Investigator's research efforts over the past decade. Current research addresses problems associated with the standard model for the outbursts of the classical novae: the occurrence of thermonuclear runaways (TNR) in the accreted hydrogen rich envelopes on white dwarfs in close binary systems (see, e.g., the reviews by Truran 1982; and Shara 1989). Research in progress and planned for the next three years has three main objectives: (1) to gain an improved understanding of the early evolution of the light curves of, particularly, the fastest novae; (2) to gain an improved understanding of the relative importance of the various possible mechanisms of envelope hydrogen depletion (e.g. winds, common envelope driven mass loss, and nuclear burning) to the long term evolution of novae in outburst; and (3) to seek to provide a somewhat more definitive statement of the role of classical novae in nucleosynthesis. Our proposed 2-D studies of convection during the early phases of the TNR and our systematic attempt to incorporate an improved treatment of radiation hydrodynamics into the hydrodynamic code utilized in our calculations, are particularly relevant to the first of these objectives. Further 2-D studies of the effects of common envelope evolution are intended to provide more realistic constraints on the mass depletion mechanisms. Finally, detailed calculations of the thermonuclear history of the matter ejected in novae will be carried out for representative nova configurations involving both carbon-oxygen (CO) and oxygen-neon-magnesium (ONeMg) white dwarfs.
    Keywords: ASTROPHYSICS
    Type: NASA-CR-200193 , NAS 1.26:200193 , NIPS-96-08389
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  • 2
    Publication Date: 2019-07-13
    Description: The progress made during 1995 on the Monte-Carlo gamma-ray spectrum simulation program BSIMUL is discussed. Several features have been added, including the ability to model shields that are tapered cylinders. Several simulations were made on the Near Earth Asteroid Rendezvous detector.
    Keywords: ASTROPHYSICS
    Type: NASA-CR-200089 , NAS 1.26:200089 , NIPS-96-07659
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  • 3
    Publication Date: 2019-06-28
    Description: The funds from this grant were used to support observations and analysis with the International Ultraviolet Explorer (IUE) satellite telescope. The main area of scientific research concerned the variability analyses of ultraviolet spectra of Active Galactic Nuclei, primarily quasars, Seyfert galaxies, and BL Lacertae objects. The Colorado group included, at various times, the P.I. (J.M. Shull), Research Associate Dr. Rick Edelson, and graduate students Jon Saken, Elise Sachs, and Steve Penton. A portion of the work was also performed by CU undergraduate student Cheong-ming Fu. A major product of the effort was a database of all IUE spectra of active galactic nuclei. This database is being analyzed to obtain spectral indices, line fluxes, and continuum fluxes for over 500 AGN. As a by-product of this project, we implemented a new, improved technique of spectral extraction of IUE spectra, which has been used in several AGN-WATCH campaigns (on the Seyfert galaxy NGC 4151 and on the BL Lac object PKS 2155-304).
    Keywords: ASTROPHYSICS
    Type: NASA-CR-200196 , NAS 1.26:200196 , NIPS-96-08385
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  • 4
    Publication Date: 2019-04-02
    Description: Five bright gamma-ray bursts (GRBs) detected by the Burst and Transient Source Experiment (BATSE) have also been detected at higher energies by EGRET. Four are consistent with power-law spectra extending to energies as high as, in the case of GRB930131, 1 GeV. The fifth, and most recent, GRB940217, has a more complex spectrum, with one photon detected at 18 GeV, the most energetic GRB photon detection to date. The optical depth to photon-photon pair production in these sources is extremely large for distances more than about 10pc away if the radiation is emitted isotropically in the observer's frame. This optical depth can be dramatically reduced if the source is moving with a relativstic bulk Lorentz factor Gamma, and recent calculations for this situation have been limited to cases of a beam with opening angle 1 Gamma, or expansions of infinitely thin spherical shells. This paper presents our extension of the pair production otpical depth calculation in relativistically expanding sources to more general geometries, including shells of finite thickness and arbitrary opening angle. We find that the minimum bulk Lorentz factors for the Energy Gamma Ray Experiment Telescope (EGRET) sources to be optically thin, i.e. display no spectral attenuation, is only moderately dependent on the shell thickness and its opening solid angle; these new limits on required velocity for given geometries will aid in placing realistic constraints on GRB source models.
    Keywords: ASTROPHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 15; 5; p. (5)153-(5)156
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  • 5
    Publication Date: 2019-04-02
    Description: The new method of statistical studying of cosmic gamma-ray bursts is presented based on the averaging of time profiles. The comparison is done between bright and dim events: while no differences were found between average flux curves, the hardness ratios pointed out the effect of hardness/brightness correlation.
    Keywords: ASTROPHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 15; 5; p. (5)131-(5)134
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  • 6
    Publication Date: 2019-04-02
    Description: The Thomson limit of resonant inverse Compton scattering in the strong magnetic fields of neutron stars is considered as a mechanism for producing gamma-ray burst continuum spectra. Photon production spectra and electron cooling rates are presented using the full magnetic Thomson cross-section. Model emission spectra are obtained as self-consistent solutions of a set of photon and electron kinetic equations, displaying spectral breaks and other structure at gamma-ray energies.
    Keywords: ASTROPHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 15; 5; p. (5)85-(5)88
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  • 7
    Publication Date: 2011-08-24
    Description: The depletion of condensable elements onto grains in gaseous nebulae can provide evidence that dust is well mixed with the ionized gas. Al and CA are two of the most depleted elements in the general interstellar medium, and it is therefore important to measure their abundances within the ionized region of nebulae. We compute a large grid of photoionization models and identify sets of line ratios which are relatively insensitive to stellar and nebular parameters, and are thus excellent diagnostics for determining relative abundances. Based on the absence of the ((Ca II) lambda lambda 291, 7324 doublet and the detection of Al II) lambda lambda 2660, 2669 in the ultraviolet, we determine the extent of aluminum and calcium depletion onto grains in NGC 7027 and the Orion Nebula. Our results show a approximately 0.3 dex depletion for Al, but a depletion of more than two and a half orders of magnitude for Ca. A similar calculation based on Mg II lambda 2798 yields roughly a 0.8 dex depletion for Mg. This reaffirms the discrepancy between depletion determined from high and low ionization Mg lines. We also find evidence for a 'depletion gradient' in Ca in NGC 7027, since the calcium depletion we infer for the outer, more neutral regions using (Ca II) is somewhat higher than that inferred for the inner high-ionization region, using (Ca v). This gradient can test current models of the survival of grains within hot ionized gas.
    Keywords: ASTROPHYSICS
    Type: The Astrophysical Journal, Part 1 (ISSN 0004-637X); 439; 2; p. 793-799
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  • 8
    Publication Date: 2011-08-24
    Description: We investigate the physical basis for the timescale of impulsive-phase, redshifted Lyman-alpha emission in stellar flares on the assumption that it is determined by energy losses in a nonthermal proton beam that is penetrating the chromosphere from above. The temporal evolution of ionization and heating in representative model chromospheres subjected to such beams is calculated. The treatment of 'stopping' of beam protons takes into account their interactions with (1) electrons bound in neutral hydrogen, (2) nuclei of neutral hydrogen, (3) free electrons, and (4) ambient thermal protons. We find that, for constant incident beam flux, the system attains an equilibrium with the beam energy input to the chromosphere balanced by radiative losses. In equilibrium, the beam penetration depth is constant, and erosion of the chromosphere ceases. If the redshifted, impulsive-phase stellar flare Lyman-alpha emission is produced by downstreaming hydrogen formed through charge exchange between beam protons and ambient hydrogen, then the emission should end when the beam no longer reaches neutral hydrogen. The durations of representative emission events calculated on this assumption range from 0.1 to 14 s. The stronger the beam, the shorter the timescale over which the redshifted Lyman-alpha emission can be observed.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 441; 1; p. 385-399
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  • 9
    Publication Date: 2011-08-24
    Description: The second guide star catalog (GSC-2) is a project that aims to create a complete catalog of stars and galaxies to about the 18th magnitude, and would contain colors, magnitudes, positions and proper motions. The catalog would provide an object list for the construction of an input catalog for possible future astrometric satellites, such as the global astrometric interferometer for astrophysics (GAIA) satellite. With a schedule that is compatible with the projected timeframe of GAIA, the GSC-2 could be available in time to support the preparatory astrophysical observations for an input catalog. The availability of the digitalized images for the preparation of finding charts would improve the efficiency of this task.
    Keywords: ASTROPHYSICS
    Type: ESA, Future Possibilities for Astrometry in Space; p 137-141
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  • 10
    Publication Date: 2011-08-24
    Description: A direct link to an extragalactic reference system is considered as being a principle aim of the global astrometric interferometer for astrophysics (GAIA) mission. The data available from an extragalactic data base and a quasi stellar object (QSO) catalog were used to obtain an estimation of the number of QSO link candidates. The quality of presently available data and the expected accuracy of the extragalactic link are discussed. It is concluded that at least 150 QSO's must be observed by GAIA in order to guarantee an accuracy of better than 1 microarcsec/year for the link. New observations will be needed before the GAIA launch in order to reduce uncertainties in the positions, magnitudes and redshifts for some known quasars. The variability of QSO's with magnitudes near the GAIA observation limit can raise a potential problem. The motions of nearby QSO's are expected to be much smaller than 2 microarcsec/year, and therefore, will not affect the accuracy of the link in the proposed GAIA mission.
    Keywords: ASTROPHYSICS
    Type: ESA, Future Possibilities for Astrometry in Space; p 127-129
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  • 11
    Publication Date: 2011-08-24
    Description: The power laws are approximately f(exp -1.9), f(exp -1.9), and f(exp -2.1) respectively for the Grigg-Shjellerup (GS), Giacobini-Zinner (GZ), and Halley (H) comets. Other than similarities in the power spectra, the magnetic field turbulence is considerably different at the three comets. Phase steepening is demonstrated to occur at the trailing edges of the GS waves. This is probably due to nonlinear steepening plus dispersion of the left-hand mode components, i.e., the turbulence is whistler-mode. This too can be explained by nonlinear steepening plus dispersion of the magnetosonic waves. At the level of GS and GZ turbulence development when the spacecraft measurements were made, classical three-wave processes, such as the decay or modulation instabilities do not appear to play important roles. It is most likely that the nonlinear steepening and dispersive time scales are more rapid than three-wave processes, and the latter had not had time to develop for the relatively new turbulence. The wave turbulence at Halley is linearly polarized. The exact nature of this turbulence is still not well understood. Several possibilities are suggested, based on a preliminary analyses.
    Keywords: ASTROPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 22; 9; p. 1149-1152
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  • 12
    Publication Date: 2011-08-24
    Description: Near-infrared images of the Galactic bulge at 1.25, 2.2, 3.5, and 4.9 microns obtained by the Diffuse Infrared Background Experiment (DIRBE) onboard the Cosmic Background Explorer (COBE) satellite are used to characterize its morphology and to determine its infrared luminosity and mass. Earlier analysis of the DIRBE observations (Weiland et al. 1994) provided supporting evidence for the claim made by Blitz & Spergel (1991) that the bulge is bar-shaped with its near end in the first Galactic quadrant. Adopting various triaxial analytical functions to represent the volume emissivity of the source, we confirm the barlike nature of the bulge and show that triaxial Gaussian-type functions provide a better fit to the data than other classes of functions, including an axisymmetric spheroid. The introduction of a `boxy' geometry, such as the one used by Kent, Dame, & Fazio (1991) improves the fit to the data. Our results show that the bar is rotated in the plane with its near side in the first Galactic quadrant creating an angle of 20 deg +/- 10 deg between its major axis and the line of sight to the Galactic center. Typical axis ratios of the bar are (1:0.33 +/- 0.11:0.23 +/- 0.08), resembling the geometry of prolate spheroids. There is no statistically significant evidence for an out-of-plane tilt of the bar at 2.2 microns, and marginal evidence for a tilt of approximately equal 2 deg at 4.9 microns. The introduction of a roll around the intrinsic major axis of the bulge improves the `boxy' appearance of some functions. A simple integration of the observed projected intensity of the bulge gives a bulge luminosity of 1.2 x 10(exp 9), 4.1 x 10(exp 8), 2.3 x 10(exp 8), and 4.3 x 10(exp 7) solar luminosity, respectively, at 1.25, 2.2, 3.5, and 4.9 microns wavelength for a Galactocentric distance of 8.5 kpc. The 2.2 microns luminosity function of the bulge population in the direction of Baade's window yields a bolometric luminosity of L(sub bol) = 5.3 x 10(exp 9) solar luminosity. Stellar evolutionary models relate this luminosity to the number of main-sequence progenitor stars that currently populate the red giant branch. Combined with the recent determination of the main-sequence turnoff mass for the bulge by the Hubble Space Telescope (Holtzman et al. 1993) we derive a photometrically determined bulge mass of approximately equal to 1.3 x 10(exp 10) solar mass for a Salpeter initial mass function extended down to 0.1 solar mass.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 445; 2; p. 716-730
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  • 13
    Publication Date: 2011-08-24
    Description: We have produced two-dimensional maps of the intensity ratio, Q(sub 60), of 60 micron infrared to 20 cm radio continuum emission, for a set of 25 nearby galaxies, mostly spirals. The ratio maps were obtained from infrared images made using IRAS data with the maximum correlation method, and radio images made using VLA data. Before taking the ratio, the radio images were processed so as to have the same resolution properties as the infrared images; the final spatial resolution in all cases is approximately 1 min, corresponding to 1 - 2 kpc for most galaxies. This resolution represents a significant improvement over previous studies. Our new high-resolution maps confirm the slow decrease of Q(sub 60) with increasing radial distance from the nucleus, but show additional structure which is probably associated with separate sites of active star formation in the spiral arms. The maps show Q(sub 60) to be more closely related to infrared surface brightness than to the radial distance r in the galaxy disk. We note also that the Q(sub 60) gradients are absent (or at least reduced) for the edge-on galaxies, a property which can be attributed to the dilution of contrast due to the averaging of the additional structure along the line of sight. The results are all in qualitative agreement with the suggestion that the radio image represents a smeared version of the infrared image, as would be expected on the basis of current models in which the infrared-radio correlation is driven by the formation of massive stars, and the intensity distribution of radio emission is smeared as a result of the propagation of energetic electrons accelerated during the supernova phase.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 445; 2; p. 599-606
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  • 14
    Publication Date: 2011-08-24
    Description: A calculation, employing a detailed model of neutral oxygen, is carried out to give fluorescent line intensities expected in a long-proposed photoexcitation by accidental resonance (PAR) process in which hydrogen Lyman-beta photoexcites the oxygen spectrum. The results pertain to the optically thin case but provide an upper limit to the fluorescent intensities which can be attained. They are applied to analyze line ratios involving the strong 8446 A line observed in classical novae during the diffusion-enhanced and Orion phases. Operation of the PAR process in the novae is verified. It is found that photoexcitation rates in the ejecta reach values greater than 0.1/sec, corresponding to hydrogen Lyman-beta radiation field intensities greater than 1250 ergs/cm/sec/sr.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 439; 1; p. 346-356
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  • 15
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    In:  Other Sources
    Publication Date: 2011-08-24
    Description: Thermal drag, a variant of the Yarkovsky effect, may act on small asteroids with sizes from a few meters to a few tens of meters. Yarkovsky thermal drag comes from an asteroid's absorbing sunlight in the visible and reradiating it in the infrared. Since the infrared photons have momentum, by action-reaction, they kick the asteroid when they leave its surface. The reradiation, which is asymmetric in latitude over the asteroid, gives a net force along the asteroid's pole. Due to the asteroid's thermal inertia, averaging this force over one orbital period produces a net drag if the spin axis has a component in the orbital plane. Thermal drag tends to circularize orbits. It can increase or decrease orbital inclinations. An object whose spin axis points in random directions over its lifetime displays little change in orbital inclination. Thermal drag appears to have little to do with the delivery of chondrites from the asteroid belt; the thermal drag timescale (10(exp 8) years for meter-sizzed objects) is long compared with their cosmic ray exposure ages, and aphelia in the asteroid belt are not expected for mature thermal drag orbits. However, Yarkovsky thermal drag may act on the recently discovered near-Earth asteroids, which have radii of 10-30 m. Asteroid 1992 DA, for instance, might have its orbit shrunk by 0.1 AU in 3 x 10(exp 7) years, removing it from an Earth-crossing orbit. The near-Earth asteroids also tend to have small to moderate orbital eccentricities, as expected for highly evolved thermal drag objects. However, the time needed to bring them in from the asteroid belt (about 10(exp 9) years) is long compared with the collisonal and dynamical lifetimes (both about 10(exp 8) years) for Earth-crossing objects, arguing against their emplacement by thermal drag.
    Keywords: ASTROPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 100; E1; p. 1585-1594
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  • 16
    Publication Date: 2011-08-24
    Description: The modern scenario of evolution of massive binary systems predicts the existence of a subclass of binary radio pulsars (PSRs) with black holes (BHs). Their Galactic number was evaluated as approximately 1 per 1000 single pulsars (Lipunov et al. 1994b). Distinctive properties of such binaries would be (1) mass of the unseen companion M(sub c) greater than 3-4 solar mass and (2) absence of eclipses of the pulsar radiation with no distinctive variance of the dispersion measure along the pulsar orbit. The pulsars themselves must be similar to standard isolated ones. The recently discovered binary 1 s pulsar PSR B0042-73 = PSR J0045-7319 in the Small Magellanic Cloud (SMC) with a massive companion in a highly elongated (eccentricity e =0.8) 51 day orbit (Kaspi et al. 1994) may be the first such pulsar with a BH. The paradoxical fact that the first pulsar discovered in the SMC proved to be in a binary system can be naturally understood if its companion actually is a 10-30 solar mass black hole. We illustrate this fact by the numerical calculation of evolution of radio pulsars after a star formation burst.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 441; 2; p. 776-778
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  • 17
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    In:  Other Sources
    Publication Date: 2011-08-24
    Description: Four spectral emission features of the N(sub KK) = 4(sub 04) -3(sub 13) rotational transition of methylene (CH2) have been detected at signal levels 5-7 sigma above noise toward the hot core of the Orion-KL nebula and the molecular cloud in proximity to the continuum source W51 M. Specifically, in both sources we have resolved the F = 6-5, 5-4, and 4-3 hyperfine transitions of the J = 5-4 fine-structure levels and detected the blended hyperfine structure of the J = 4-3 fine structure levels. At the J = 3-2 fine-structure levels, we have observed new transitions of NS, a known interstellar molecule, which severely contaminates the search for CH2 hyperfine transitions. These new sensitive observations finally confirm the existence of interstellar CH2 which was tentatively reported by us some years ago.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 438; 1; p. 259-264
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  • 18
    Publication Date: 2011-08-24
    Description: We have simulated full-sky maps of the cosmic microwave background (CMB) anisotropy expected from cold dark matter (CDM) models at 0.5 deg and 1.0 deg angular resolution. Statistical properties of the maps are presented as a function of sky coverage, angular resolution, and instrument noise, and the implications of these results for observability of the Doppler peak are discussed. The rms fluctuations in a map are not a particularly robust probe of the existence of a Doppler peak; however, a full correlation analysis can provide reasonable sensitivity. We find that sensitivity to the Doppler peak depends primarily on the fraction of sky covered, and only secondarily on the angular resolution and noise level. Color plates of the simulated maps are presented to illustrate the anisotropies.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 441; 1; p. L1-L4
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  • 19
    Publication Date: 2011-08-24
    Description: The COMPTEL sky map of the 1.8 MeV line emission from Al-26 shows an extended diffuse distribution along the Galactic plane with a peculiar large scale asymmetry about the Galactic center (GC) and a clumpy structure with several noticeable hot spots. The most prominent hot spot at the GC appears shifted to positive longitude by about 2 deg. Nearby supernova remnants or Wolf-Rayet stars are plausible explanations for individual hot spots such as in the Vela region. We show that the global asymmetry and most hot spots can be understood by a more general model: the Al-26 sources are confined in the spiral arms of our Galaxy, and coagent star formation is responsible for additional clumpiness. The off-centered GC hot spot is probably due to the observed asymmetrically distributed circumnuclear molecular gas interacting with a central stellar bar, whose existence has been inferred from IR observations.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 440; 2; p. L57-L60
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  • 20
    Publication Date: 2011-08-24
    Description: Soft gamma repeaters are characterized by recurrent activity consisting of short-duration outbursts of high-energy emission that is typically of temperature less than 40 keV. One recent model of repeaters is that they originate in the environs of neutron stars with superstrong magnetic fields, perhaps greater than 10(exp 14) G. In such fields, the exotic process of magnetic photon splitting gamma yields gamma gamma acts very effectively to reprocess gamma-ray radiation down to hard X-ray energies. In this Letter, the action of photon splitting is considered in some detail, via the solution of photon kinetic equations, determining how it limits the hardness of emission in strongly magnetized repeaters, and thereby obtaining observational constraints to the field in SGR 1806-20.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 440; 2; p. L69-L72
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  • 21
    Publication Date: 2013-08-31
    Description: We discuss the Shannon-Wehrl entropy within the squeezing vocabulary for the cosmological and black hole particle production.
    Keywords: ASTROPHYSICS
    Type: NASA. Goddard Space Flight Center, Second International Workshop on Harmonic Oscillators; p 359-362
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  • 22
    Publication Date: 2013-08-31
    Description: The LDEF contained 57 individual experiment trays or tray portions specifically designed to characterize critical aspects of meteoroid and debris environment in low-Earth orbit (LEO). However, it was realized from the beginning that the most efficient use of the satellite would be to characterize impact features from the entire surface of the LDEF. With this in mind particular interest has focused on common materials facing in all 26 LDEF facing directions; among the most important of these materials has been the tray clamps. Therefore, in an effort to better understand the nature and flux of particulates in LEO, and their effects on spacecraft hardware, we are analyzing residues found in impact features on LDEF tray clamp surfaces. This paper summarizes all data from 79 clamps located on Bay A & B of the LDEF. We also describe current efforts to characterize impactor residues recovered from the impact craters, and we have found that a low, but significant, fraction of these residues have survived in a largely unmelted state. These residues can be characterized sufficiently to permit resolution of the impactor origin. We have concentrated on the residue from chondritic interplanetary dust particles (micrometeoroids), as these represent the harshest test of our analytical capabilities.
    Keywords: ASTROPHYSICS
    Type: NASA. Langley Research Center, LDEF: 69 Months in Space. Third Post-Retrieval Symposium, Part 1; p 401-413
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  • 23
    Publication Date: 2013-08-31
    Description: This study is a further investigation of space-exposed samples recovered from the LDEF satellite and the Franco-Russian 'Aragatz' dust collection experiment on the Mir Space Station. Impact craters with diameters ranging from 1 to 900 micron were found on the retrieved samples. Elemental analysis of residues found in the impact craters was carried out using Energy Dispersive X-ray spectrometry (EDX). The analyses show evidence of micrometeoroid and orbital debris origins for the impacts. The proportions of these two components vary according to particle size and experimental position with respect to the leading edge of the spacecraft. On the LDEF leading edge 17 percent of the impacts were apparently caused by micrometeoroids and 11 percent by debris; on the LDEF trailing edge 23 percent of the impacts are apparently caused by micrometeoroids and 4 percent consist of debris particles - mostly larger than 3 micron in diameter - in elliptical orbits around the Earth. For Mir, the analyses indicate that micrometeoroids form 23 percent of impacts and debris 9 percent. However, we note that 60-70 percent of the craters are unidentifiable, so the definitive proportions of natural v. man-made particles are yet to be determined. Experiments carried out using a light gas gun to accelerate glass spheres and fragments demonstrate the influence of particle shape on crater morphology. The experiments also show that it is more difficult to analyze the residues produced by an irregular fragment than those produced by a spherical projectile. If the particle is travelling above a certain velocity, it vaporizes upon impact and no residues are left. Simulation experiments carried out with an electrostatic accelerator indicate that this limit is about 14 km/s for Fe particles impacting Al targets. This chemical analysis cut-off may bias interpretations of the relative populations of meteoroid and orbital debris. Oblique impacts and multiple foil detectors provide a higher likelihood of detection of residues as the velocities involved are lower.
    Keywords: ASTROPHYSICS
    Type: NASA. Langley Research Center, LDEF: 69 Months in Space. Third Post-Retrieval Symposium, Part 1; p 431-444
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  • 24
    Publication Date: 2013-08-31
    Description: Approximately 1000 impact craters on the Chemistry of Meteoroid Experiment (CME) have been analyzed by means of Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Analysis (EDXA) to determine the compositional make-up of projectile residues. This report completes our systematic survey of gold and aluminum surfaces exposed at the trailing-edge (A03) and forward-facing (A11) LDEF sites, respectively. The major categories for the projectile residues were (1) natural, with diverse subgroups such as chondritic, monomineralic silicates, and sulfides, and (2) man made, that were classified into aluminum (metallic or oxide) and miscellaneous materials (such as stainless steel, paint flakes, etc). On CME gold collectors on LDEF's trailing edge approximately 11 percent of all craters greater than 100 micron in diameter were due to man-made debris, the majority (8.6 percent) caused by pure aluminum, approximately 31.4 percent were due to cosmic dust, while the remaining 58 percent were indeterminate via the analytical techniques utilized in this study. The aluminum surfaces located at the A11 forward-facing site did not permit analysis of aluminum impactors, but approximately 9.4 percent of all craters were demonstratably caused by miscellaneous debris materials and approximately 39.2 percent were the result of natural particles, leaving approximately 50 percent which were indeterminate. Model considerations and calculations are presented that focus on the crater-production rates for features greater than 100 micron in diameter, and on assigning the intermediate crater population to man-made or natural particles. An enhancement factor of 6 in the crater-production rate of natural impactors for the 'forward-facing' versus the 'trailing-edge' CME collectors was found to best explain all observations (i.e., total crater number(s), as well as their computational characteristics). Enhancement factors of 10 and 4 are either too high or too low. It is also suggested that approximately 45 percent of all craters greater than 100 micron in diameter are caused by man-made impactors on the A11 surfaces. This makes the production rate for craters greater than 100 micron in diameter, resulting from orbital debris, a factor of 40 higher on the forward-facing sides as opposed to the trailing-edge direction.
    Keywords: ASTROPHYSICS
    Type: NASA. Langley Research Center, LDEF: 69 Months in Space. Third Post-Retrieval Symposium, Part 1; p 415-429
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  • 25
    Publication Date: 2013-08-31
    Description: Examination of LDEF's various surfaces shows numerous craters and holes due to hypervelocity impacts of meteoroids and man-made orbital debris. In this paper, the crater numbers as reported by Humes have been analyzed in an effort to understand the orbital debris and natural meteoroid environment in LEO. To determine the fraction of man-made to natural impacts, the side to top ratio of impacts and results of the Chemistry of Micrometeoroids Experiment are used. For craters in the 100 micron to 500 micron size range, about 25 percent to 30 percent of the impacts on the forward-facing surfaces and about 10 percent of the impacts on the trailing surfaces were estimated due to man-made orbital debris. A technique has been developed to convert crater numbers to particle fluxes, taking the fact into account that the distributions of impact velocity and incidence angle vary over the different surfaces of LDEF, as well as the ratio of the surface area flux to the cross-sectional area flux. Applying this technique, Humes' data concerning craters with limiting lip diameters of 100 micron, 200 micron and 500 micron have been converted into orbital debris and meteoroid fluxes ranging from about 20 micron to 200 micron particle diameter. The results exhibit good agreement with orbital debris model and meteoroid model. The converted meteoroid flux is slightly larger than Grun's model (by 40 to 70 percent). The converted orbital debris flux is slightly lower than Kessler's model for particle diameter smaller than about 30 micron and slightly larger than the model for particle diameter larger than about 40 micron. Taking also into account the IDE data point at about 0.8 micron particle diameter, it suggests to change the slope log (flux) versus log (diameter) of orbital debris flux in the 1 micron to 100 micron particle diameter range from 2.5 to 1.9.
    Keywords: ASTROPHYSICS
    Type: NASA. Langley Research Center, LDEF: 69 Months in Space. Third Post-Retrieval Symposium, Part 1; p 373-384
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  • 26
    Publication Date: 2013-08-31
    Description: Comets are recognized as among the most scientifically important objects in the solar system. They are presumed relics of the early primitive material in the solar nebula and are believed to have provided a general enrichment of volatiles to the inner solar system. The Cometary Coma Chemical Composition (C4) Mission, a proposed Discovery-Class Mission, will analyze materials released into the coma, providing information leading to the understanding of the chemical composition and make-up of the cometary nucleus. As one of two scientific instruments in the C4 spacecraft, an advanced and streamlined version of the Cometary Ice and Dust Experiment (CIDEX), a mini-CIDEX, will employ an X-Ray Fluorescence (XRF) spectrometer to determine bulk elemental composition of cometary dust grains and a Gas Chromatograph/Ion Mobility Spectrometer (GC/IMS) for determination of the molecular composition of dust and ices following stepwise pyrolysis and combustion. A description of the mini-CIDEX IMS will be provided as well as data from analyses conducted using the mini-CIDEX breadboard instrument.
    Keywords: ASTROPHYSICS
    Type: NASA. Johnson Space Center, Third International Workshop on Ion Mobility Spectrometry; p 57-65
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  • 27
    Publication Date: 2013-08-31
    Description: The Orbiting Meteoroid and Debris Counting Experiment (OMDC) flew for approximately 90 days in a highly elliptical earth orbit onboard the Clementine Interstage Adapter (ISA) Spacecraft. This experiment obtained data on the impact flux of natural micrometeoroids and it provided limited information on the population of small mass man-made debris as a function of altitude in near earth space. The flight of the OMDC experiment on the ISA spacecraft also demonstrated that the ultra-lightweight, low-power, particle impact detector system that was used is a viable system for flights on future spacecraft to monitor the population of small mass man-made debris particles and to map the cosmic dust environment encountered on interplanetary missions. An overview of the ISA spacecraft mission, the approach to the OMDC experiment, and the data obtained by the experiment are presented.
    Keywords: ASTROPHYSICS
    Type: LDEF: 69 Months in Space. Third Post-Retrieval Symposium, Part 3; p 1331-1340
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  • 28
    Publication Date: 2011-08-24
    Description: We report the results from observations of National Radio Astronomy Observatory (NRAO) 140 carried out in the X-ray band using ROSAT and Advanced Satellite for Cosmology and Astrophysics (ASCA) in 1992 and 1994. We find the source to be absorbed by an effective hydrogen column density of approximately 3 x 10(exp 21) atoms/sq cm during both epochs, consistent with the combined atomic and molecular column inferred from radio measurements along this line of sight through the Perseus cloud complex. We compare these results with previous X-ray absorption measurements and briefly comment upon the origin of the excess absorption which has been seen toward this source. We find the ASCA spectrum of NRAO 140 is well described by a power law of energy index alpha = 0.73 +/- 0.03 and also yields the tightest constraint to date on Fe K-shell emission, with 90% confidence upper limits of 38 and 31 eV for a narrow line at a rest frame energy of 6.4 and 6.7 keV respectively. This, along with a lack of hardening towards higher energies, suggests that either NRAO 140 is devoid of cold reprocessing material, the reprocessing material has a geometry in which the imprinted features are weak, and/or the X-ray emission is relativistically beamed towards us. We also report the detection of a serendipitous source in both the Advanced Satellite for Cosmology and Astrophysics Gas Imaging Spectrometer (ASCA GIS) and ROSAT fields of view. We identify this source as the binary star system IX Per and find its spectrum to be well fitted by a two-temperature Raymond-Smith plasma.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 445; 2; p. 660-665
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  • 29
    facet.materialart.
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    In:  Other Sources
    Publication Date: 2011-08-24
    Description: Titan's large free eccentricity results in significant tidal dissipation. This can be used to constrain the existence and depth of hydrocarbon oceans. A hydrodynamical-numerical 2 deg ocean tide model has been constructed to investigate this connection. The model allows some simple land configurations. The results indicate that existence of such an ocean over the age of the solar system is hard to explain, as is the existence of the large eccentricity itself. If such an ocean exists, it is likely to be more than 500 m deep, ignoring the influence of land masses.
    Keywords: ASTROPHYSICS
    Type: Icarus (ISSN 0019-1035); 113; 1; p. 39-56
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  • 30
    Publication Date: 2011-08-24
    Description: The Monte Carlo technique of simulating diffusive particle acceleration at shocks has made spectral predictions that compare extremely well with particle distributions observed at the quasi-parallel region of the earth's bow shock. The current extension of this work to compare simulation predictions with particle spectra at oblique interplanetary shocks has required the inclusion of significant cross-field diffusion (strong scattering) in the simulation technique, since oblique shocks are intrinsically inefficient in the limit of weak scattering. In this paper, we present results from the method we have developed for the inclusion of cross-field diffusion in our simulations, namely model predictions of particle spectra downstream of oblique subluminal shocks. While the high-energy spectral index is independent of the shock obliquity and the strength of the scattering, the latter is observed to profoundly influence the efficiency of injection of cosmic rays into the acceleration process.
    Keywords: ASTROPHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 15; 8-9; p. 397-400
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  • 31
    Publication Date: 2011-08-24
    Description: 24 years of Lunar Laser Ranging (LLR) observations and 16 years of Very Long Baseline Interferometry (VLBI) observations are combined in a global analysis to yield improved estimates of the Earth's precession and nutation. The correction to the International Astronomical Union (IAU) (1976) precession constant inferred from this joint VLBI/LLR analysis is -3.00 +/- 0.20 milliarcsec/yr (mas/yr). A significant obliquity rate correction of -0.20 +/- 0.08 mas/yr is also found. In all, 32 forced nutation coefficients are estimated. These coefficients confirm that the IAU (1980) nutation theory is in error by several mas. The estimated nutation coeficients are found to vary by as much as several tenths of mas, depending on the a priori nutation model used to analyze the VLBI and LLR data. Forced circular nutations derived from this analysis agree with the ZMOA-1990-2 nutation theory at the 0.2 mas level for the 18.6 yr terms, and at the 0.05 mas level for the other terms (periods less than or = 1 yr). A retrograde free core nutation with an amplitude of 0.20 mas is also detected. Its phase is found to be very sensitive to the precise value of the free core nutation period used in the solution. Separate analyses of four independent subsets of the LVBI data indicate no significant variations of the free core nutation since 1988. The pre-1988 estimates of the free core nutation are consistent with the post-1988 estimates but are not accurate enough to rule out possible variations of the free core nutation at these earlier epochs.
    Keywords: ASTROPHYSICS
    Type: The Astronomical Journal (ISSN 0004-6256); 109; 1669; p. 418-427
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  • 32
    facet.materialart.
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    In:  Other Sources
    Publication Date: 2011-08-24
    Description: We calculate the structure of an effectively optically thin and geometrically thin accretion disk in the Kerr geometry, including electron-positron pairs. We show that the properties of the disk solutions are strongly dependent on the angular momentum of the central black hole. We find that close to a rapidly rotating hole there can be an appreciable pair density even for modest accretion rates. Pair critical accretion rates recently discovered in Newtonian disk models are also shown to be present in the general relativistic models, and we show that the geometrically thin disk approximations easily break down for rapidly rotating holes.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 441; 2; p. 765-769
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  • 33
    Publication Date: 2011-08-24
    Description: A standard problem in gamma-ray astronomy data analysis is the decomposition of a set of observed counts, described by Poisson statistics, according to a given multicomponent linear model, with underlying physical count rates or fluxes which are to be estimated from the data. Despite its conceptual simplicity, the linear least-squares (LLSQ) method for solving this problem has generally been limited to situations in which the number n(sub i) of counts in each bin i is not too small, conventionally more than 5-30. It seems to be widely believed that the failure of the LLSQ method for small counts is due to the failure of the Poisson distribution to be even approximately normal for small numbers. The cause is more accurately the strong anticorrelation between the data and the wieghts w(sub i) in the weighted LLSQ method when square root of n(sub i) instead of square root of bar-n(sub i) is used to approximate the uncertainties, sigma(sub i), in the data, where bar-n(sub i) = E(n(sub i)), the expected value of N(sub i). We show in an appendix that, avoiding this approximation, the correct equations for the Poisson LLSQ (PLLSQ) problems are actually identical to those for the maximum likelihood estimate using the exact Poisson distribution. We apply the method to solve a problem in high-resolution gamma-ray spectroscopy for the JPL High-Resolution Gamma-Ray Spectrometer flown on HEAO 3. Systematic error in subtracting the strong, highly variable background encountered in the low-energy gamma-ray region can be significantly reduced by closely pairing source and background data in short segments. Significant results can be built up by weighted averaging of the net fluxes obtained from the subtraction of many individual source/background pairs. Extension of the approach to complex situations, with multiple cosmic sources and realistic background parameterizations, requires a means of efficiently fitting to data from single scans in the narrow (approximately = 1.2 keV, HEAO 3) energy channels of a Ge spectrometer, where the expected number of counts obtained per scan may be very low. Such an analysis system is discussed and compared to the method previously used.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 438; 1; p. 322-340
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  • 34
    Publication Date: 2011-08-24
    Description: The topology of the magnetic field in the heliosheath is illustrated using plots of the field lines. It is shown that the Archimedean spiral inside the terminal shock is rotated back in the heliosheath into nested spirals that are advected in the direction of the interstellar wind. The 22-year solar magnetic cycle is imprinted onto these field lines in the form of unipolar magnetic envelopes surrounded by volumes of strongly mixed polarity. Each envelope is defined by the changing tilt of the heliospheric current sheet, which is in turn defined by the boundary of unipolar high-latitude regions on the Sun that shrink to the pole at solar maximum and expand to the equator at solar minimum. The detailed shape of the envelopes is regulated by the solar wind velocity structure in the heliosheath.
    Keywords: ASTROPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 100; A3; p. 3463-3471
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  • 35
    Publication Date: 2011-08-24
    Description: The star, Altair (A7 IV-V), is clearly shown to have Lyman-alpha emission of chromospheric origin, while no evidence is found for the Mg II emission reported in previous investigations. We present non-Local Thermodymanic Equilibrium (non-LTE) semiempirical models incorporating partial redistribution of the chromosphere of Altair that reproduce the observed Lyman-alpha emission and the Mg II resonance absorption at 2800 A. We unambiguously establihed that chromospheres exist at spectral types as early as A7 on the main sequence, and we also demonstrate that it very unlikely that the observed emission originates in a corotating expanding wind. This result represents a new challenge for chromospheric heating theories. It may indicate that both differential rotation and convection layers, at least near the equator, exist in this fast rotating (v sin i = 220 km/s) star.
    Keywords: ASTROPHYSICS
    Type: The Astrophysical Journal, Part 1 (ISSN 0004-637X); 439; 2; p. 1011-1020
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  • 36
    Publication Date: 2011-08-24
    Description: SN 1987A hard X-ray continuum spectra obtained on 1987 October 29, 1988 April 9-10, and 1988 November 11 from balloon-flight measurments are presented. The spectra, spanning the energy range from 25 keV to 300 keV, have been analyzed using a detector response matrix inversion technique that converts the spectra form counts/s/sq cm keV to photons/s/sq cm keV allowing direct comparison with theoretical models. The results indicate that the bulk of the (56)Co is mixed moderately through the inner regions of the supernova envelope but they do not preclude the mixing of a small amount of the (56)Co farther out into the envelope necessary to account for the observed (56)Co line fluxes. The effect of the ratio (57)Co to (56)Co on the 1988 November 11 continuum spectrum is discussed.
    Keywords: ASTROPHYSICS
    Type: The Astrophysical Journal, Part 1 (ISSN 0004-637X); 439; 2; p. 963-975
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  • 37
    Publication Date: 2011-08-24
    Description: Through analysis of available optical spectrophotometric data and radio flux density measurements in the literature, it is demonstrated that a good correlation exists between the radio power and bolometric luminosity of the optically-selected OSOs in the Bright Quasar Sample (BOS) of Schmidt and Green (1983). We have recently used VLBI measurements of a sample of ultraluminous infrared galaxies to infer the likely existence of radio-quiet Active Galactic Nuclei (AGNs) deeply enshrouded in dust within their nuclei (Lonsdale, Smith, and Lonsdale 1993). We employ the radio-bolometric luminosity correlation for the BQS quasars to test whether these hypothetical buried AGNs can be energetically responsible for the observed far-infrared luminosities of the ultraluminous infrared galaxies. The ultraluminous infrared galaxies are shown to follow the same relation between radio core power and bolometric luminosity as the radio-quiet QSOs, suggesting that buried AGNs can account for essentially all the observed infrared luminosity, and raising the possibility that any starburst which may be in progress may not be energetically dominant. The broader implications of the radio-optical correlation in quasars for AGNs and luminous infrared galaxy models and the use of radio astronomy as a probe of the central powerhouse in radio quiet AGNs and luminous infrared galaxies are briefly discussed.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 438; 2; p. 623-642
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  • 38
    facet.materialart.
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    In:  Other Sources
    Publication Date: 2011-08-24
    Description: We consider the evolution and heating of dust embedded in the hot interstellar medium of isolated elliptical galaxies. We first construct a new set of galaxy models spanning a decade in luminosity which we use to study the evolution of dust as it is ejected by stellar sources, merges and flows with the interstellar gas, and is sputtered away due to the presence of the hot gas. We find that although grains can flow a considerable distance from the parent star in some cases before being sputtering away, the grain size distribution at a given location is accurately determined by assuming in situ sputtering of dust grains as they are ejected by the parent star. We find that dust heating is dominated by absorption of ambient starlight. Heating due to collisions with energetic electrons in the hot gas and absorption of thermal X-rays is smaller by orders of magnitude. We also find that for the largest galaxy considered (L(sub B) approximately 10 (exp 11) solar luminosity) the energy lost from the hot gas due to electronic collisions with the dust is about an order of magnitude less than that lost due to thermal emission in X-rays. The gas in smaller galaxies loses even less of its energy via heating of grains. In deriving this result, we find that the inclusion of grain sputtering is a crucial ingredient of the calculation. The presence of dust grains is therefore energetically unimportant for elliptical galaxy cooling flow models.
    Keywords: ASTROPHYSICS
    Type: Astronomical Society of the Pacific, Airborne Astronomy Symposium on the Galactic Ecosystem: From Gas to Stars to Dust, Volume 73; p 177-180
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  • 39
    Publication Date: 2011-08-24
    Description: The concepts related to the operation and design of the global astrometric interferometer for astrophysics (GAIA) bring together solutions chosen for the astrometry satellite and interferometric techniques. Like the Hipparcos satellite, GAIA is a continuously scanning instrument for which the integration time on any observed object is limited by the field of view of the detector. If a final astrometric accuracy of 10 microarcsec is aimed at, a field of 1 deg in diameter is needed. A design is presented for the proposed 2.6 m baseline Fizeau interferometer with two 40 cm apertures and overall dimensions compatible with the size of the Ariane 5 payload shroud. It has a 0.9 deg diffraction limited field of view. The response of the optical system to small perturbations on each optical element is given in terms of the fringe visibility, which is shown to be dependent on the sub-aperture spot separation. The robustness of the design to thermal, mechanical and manufacturing errors is discussed. The unavoidable distortion present in wide field optical systems is analyzed in terms of displacement of the interference fringes.
    Keywords: ASTROPHYSICS
    Type: ESA, Future Possibilities for Astrometry in Space; p 241-249
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  • 40
    Publication Date: 2011-08-24
    Description: The proposed design and construction of the Fizeau astrometric mapping explorer (FAME), a small astrometric instrument for use on an artificial satellite, is reported on. The instrument and spacecraft are designed to slowly spin and will repeatedly scan great circles on the sky so that, over a period of time, it will cover the complete sky and repeat in a manner similar to that of the Hipparcos satellite. The instrument will use the two fixed dilute aperture telescopes to measure a fixed angle between stars and detect the positions, magnitude and color of all stars crossing its field of view to a visual magnitude of approximately 15 mag. The aim of the instrument is to obtain a catalog of positions, proper motions and parallaxes of all stars down to about 15 mag, with a magnitude dependent accuracy of positions of 20 to 800 micro arcsec, proper motions of 20 to 800 micro arcsec per year and parallaxes of 20 to 800 micro arcsec.
    Keywords: ASTROPHYSICS
    Type: ESA, Future Possibilities for Astrometry in Space; p 187-189
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  • 41
    Publication Date: 2011-08-24
    Description: Two dimensional spectral types for each of the stars observed in the global astrometric interferometer for astrophysics (GAIA) mission would provide additional information for the galactic structure and stellar evolution studies, as well as helping in the identification of unusual objects and populations. The classification of the large quantity generated spectra requires that automated techniques are implemented. Approaches for the automatic classification are reviewed, and a metric-distance method is discussed. In tests, the metric-distance method produced spectral types with mean errors comparable to those of human classifiers working at similar resolution. Data and equipment requirements for an automated classification survey, are discussed. A program of auxiliary observations is proposed to yield spectral types and radial velocities for the GAIA-observed stars.
    Keywords: ASTROPHYSICS
    Type: ESA, Future Possibilities for Astrometry in Space; p 169-172
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  • 42
    Publication Date: 2011-08-24
    Description: We present radio observations of the gravitational lens PKS 1830-211 at 8.4 and 15 GHz acquired using the Very Large Array. The observations were made over a 13 month period. Significant flux density changes over this period provide strong constraints on the time delay between the two lensed images and suffest a value of 44 +/- 9 days. This offers new direct evidence that this source is indeed a gravitational lens. The lens distance is dependent upon the model chosen, but reasonable limits on the mass of the lensing galaxy suggest that it is unlikely to be at a redshift less than a few tenths, and may well be significantly more distant.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 444; 2; p. 561-566
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  • 43
    Publication Date: 2011-08-24
    Description: 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.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 445; 2; p. 840-854
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  • 44
    Publication Date: 2011-08-24
    Description: We report on large-scale ab initio multiconfiguration Hartree-Fock calculations for the UV0.01 multiplet, 2s(sup 2)2p(sup 2)P(sub J) - 2s2p(sup 2 4)P(sub J prime), in N III. The resulting transition probabilities agree very well with recent semiempirical calculations, and the lifetimes for two of the three upper levels agree with experiments. The deviation for the third level is discussed. Comparisons made with the highest quality IUE echelle spectra available -- those of RR Tel and V1016 Cyg (both photoionized sources with electron densities below 10(exp 8)/cu cm) -- show that computed branching ratios of lines sharing a common upper level are in agreement with observations to within uncertainties of +/- 10%. High-quality solar limb data or stellar data from the Hubble Space Telescope (HST) could, in principle, be used to determine whether the theoretical or measured lifetimes for the discrepant level are in error. Unfortunately, stellar data for high-density plasmas (N(sub e) greater than 10(exp 11)/cu cm are needed) do not yet exist, and existing solar data lack the photometric precision to address this problem.
    Keywords: ASTROPHYSICS
    Type: The Astrophysical Journal, Part 1 (ISSN 0004-637X); 445; 1; p. 457-464
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  • 45
    Publication Date: 2011-08-24
    Description: The U-B color has been suggested as a predictor of the presence of water of hydration on asteroids. Photometry from the Eight-Color Asteroid Survey (ECAS) was used to test this concept. An overlap in U-B color prevents this magnitude difference from distinguishing between surface material that was thermally processed at higher temperatures and surface material that was aqueously altered. Two tests of the presence of water of hydration using visible spectral region photometry failed to flag those few higher albedo M- and E-class asteroids having photometry that shows a 3.0-micrometers water of hydration absorption. These asteroids probably contain little or no oxidized iron in their surface material.
    Keywords: ASTROPHYSICS
    Type: Icarus (ISSN 0019-1035); 115; 1; p. 217-218
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  • 46
    Publication Date: 2011-08-24
    Description: 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.
    Keywords: ASTROPHYSICS
    Type: Icarus (ISSN 0019-1035); 113; 1; p. 110-118
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  • 47
    Publication Date: 2011-08-24
    Description: The Ulysses spacecraft has gathered data from within flows from the Sun's southern polar coronal hole, the first in situ measurement of this region. We present a brief analysis of the heliospheric magnetic field data from this region, using a fractal method. As is the case near the ecliptic, estimated spectral exponents are near 5/3 on spacecraft scales of seconds to minutes. On longer time scales, however, there appears to be a significantly different population in polar flows, which is similar to that found by the Helios spacecraft in fast solar wind flows at 0.3 AU.
    Keywords: ASTROPHYSICS
    Type: Annales Geophysicae (ISSN 0992-7689); 13; 1; p. 105-107
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  • 48
    Publication Date: 2011-08-24
    Description: We have investigated the properties of the OMC-2 and OMC-3 cores in the Orion giant molecular cloud using high spatial spectral resolution observations of several transitions of the (13)CO, C(18)O, C(S-32) and C(S-34) molecules taken with the SEST telescope. The OMC-2 core consists of one clump (22 solar mass) with a radius of 0.11 pc surrounded by a cluster of 11 discrete infrared sources. The H2 column density and volume density in the center of this clump are 2 x 10(exp 22)/sq cm and 9 x 10(exp 5)/cu cm respectively. From a comparison between physical parameters derived from C(18)O and C(S-32) observations we conclude that the molecular envelope around the core has been completely removed by these sources and that only the very dense gas is left. OMC-3 shows a more complex elongated structure in C(18)O and CS than OMC-2. The C(S-32) and C(S-34) maps show that the denser region can be separated into at least sub-cores of roughly equal sizes (radius approximately equals 0.13 pc), with n(H2) = 6 x 10(exp 5)/cu cm, and a mass of 10 solar mass (from C(S-32)). The very different masses obtained for the central core from C(18)O and C(S-32) (55 and 12 solar mass respectively) indicate that a massive envelope is still present around the very dense sub-cores. We report the first detection of several molecular outflows in OMC-3. The presence of an IRAS source and the first detection of these outflows confirm that star formation is going on in OMC-3. Based on the different physical properties of these regions compared with OMC-1, OMC-2 appears to be in an intermediate evolutionary stage between OMC-1 and OMC-3.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 294; 3; p. 835-854
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  • 49
    Publication Date: 2011-08-24
    Description: We examine the hydrodynamic origin of relativistic outflows in active galactic nuclei (AGN). Specifically, we propose that the presence of a population of relativistic hadrons in the AGN 'central engine' and the associated neutron production suffices to produce outflows which under rather general conditions could be relativistic. The main such condition is that the size of the neutron production region be larger than the neutron flight path tau(sub n) approximately 3 x 10(exp 13) cm. This condition guarantees that the mean energy per particle in the proton fluid, resulting from the decay of the neutrons outside their production region, be greater than the proton rest mass. The expansion of this fluid can then lead naturally to a relativistic outflow by conversion of its internal energy to directed motion. We follow the development of such flows by solving the mass, energy as well as the kinetic equation for the proton gas in steady state, taking into account the source terms due to compute accurately the adiabatic index of the expanding gas, and in conjunction with Bernoulli's equation the detailed evolution of the bulk Lorentz factor. We further examine the role of large-scale magnetic fields in confining these outflows to produce the jets observed at larger scales.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 441; 2; p. 521-532
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  • 50
    Publication Date: 2011-08-24
    Description: High-contrast peaks in the cosmic microwave background (CMB) anisotropy can appear as unresolved sources to observers. We fit simluated CMB maps generated with a cold dark matter model to a set of unresolved features at instrumental resolution 0.5 deg-1.5 deg to derive the integral number density per steradian n (greater than absolute value of T) of features brighter than threshold temperature absolute value of T and compare the results to recent experiments. A typical medium-scale experiment observing 0.001 sr at 0.5 deg resolution would expect to observe one feature brighter than 85 micro-K after convolution with the beam profile, with less than 5% probability to observe a source brighter than 150 micro-K. Increasing the power-law index of primordial density perturbations n from 1 to 1.5 raises these temperature limits absolute value of T by a factor of 2. The MSAM features are in agreement with standard cold dark matter models and are not necessarily evidence for processes beyond the standard model.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 441; 1; p. L5-L7
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  • 51
    Publication Date: 2011-08-24
    Description: The UV line profile structure of high-ionization resonance lines found with the International Ultraviolet Explorer (IUE) in the brightest of four multiply imaged sources (images-A) in the candidate gravitational lens UM 425 = QSO 1120+019 indicates broad absorption line (BAL) structure. The deep-broad trough associated with the O IV line extends to velocities approiximately -12,000 km/s, and contains disrete features that suggest multicomponent velocity structure. This structure may include contributions from C IV absorption from the early-type galaxy that is believed to lens UM 425. A strong absorption feature in the blue wing of the Lyman-alpha lambda 1216 emission line may be a Lyman alpha absorption system at a Z(sub Ly alpha) = 1.437 +/- 0.003, or it may be formed by the superposition of the broad N V lambda lambda 1238, 1242 absorption trough on the extended blue emission wing of the QSO Lyman-alpha line. We obtained a redshift of Z(sub QSO) = 1.471 +/- 0.003 from Lyman-alpha lambda 1215, consistent with the redshift found by Meylan and Djorgovski in the optical. The Lyman-alpha line appears unusally weak due to the presence of N V lambda 1240 BAL absorption. A Lyman-limit absorption system at lambda 912 was not observed in the QSO rest frame. The detection of BAL structure in the other weaker ground-state resonance lines of N II (l) and S IV (l) was not found, suggesting these lines are formed in a region that is distinct from the BAL component. Detection of BAL structure in the other fainter images in this system with Hubble Space Telescope (HST) instrumentation, similar to structure observed here in image A, could provide evidence that UM 425 is a gravitational lens.
    Keywords: ASTROPHYSICS
    Type: The Astrophysical Journal, Part 1 (ISSN 0004-637X); 439; 2; p. 599-603
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  • 52
    Publication Date: 2011-08-24
    Description: We use the two-point correlation function of the extrema points (peaks and valleys) in the Cosmic Background Explorer (COBE) Differential Microwave Radiometers (DMR) 2 year sky maps as a test for non-Gaussian temperature distribution in the cosmic microwave background anisotropy. A maximum-likelihood analysis compares the DMR data to n = 1 toy models whose random-phase spherical harmonic components a(sub lm) are drawn from either Gaussian, chi-square, or log-normal parent populations. The likelihood of the 53 GHz (A+B)/2 data is greatest for the exact Gaussian model. There is less than 10% chance that the non-Gaussian models tested describe the DMR data, limited primarily by type II errors in the statistical inference. The extrema correlation function is a stronger test for this class of non-Gaussian models than topological statistics such as the genus.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 439; 2; p. L29-L32
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  • 53
    Publication Date: 2011-08-24
    Description: During its full-sky survey, the Energetic Gamma Ray Experiment Telescope (EGRET) high-energy instrument aboard the Compton Gamma-Ray Observatory detected gamma-ray emission in the energy range above 30 MeV from a source identified as the blazar PKS 0420-014. This object was observed during two separate viewing periods in 1992 February/March and May/June. An intensity decrease above 100 MeV of a factor of at least 1.5 from a maximum of (5.0 +/- 1.4) x 10(exp -7) photons 1 sq cm/s was observed during that time interval indicating extensive variability. The photon spectrum in the range between 30 and 10,000 MeV at the time of the maximum intensity is well represented by a power law with an exponent of -1.9 +/- 0.3. Some similarities with other EGRET detected blazars are briefly discussed.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 438; 2; p. 659-662
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  • 54
    Publication Date: 2013-08-29
    Description: We mapped the distribution of atomic far-IR line emission from (O I) and (C II) over parsec scales in the Galactic star-forming regions L1630, M17, and W3 using the MPE Far-Infrared Fabry-Perot Imaging spectrometer (FIFI) on board the NASA Kuiper Airborne Observatory. The lines mapped include (O I) 63 microns, (O I) 146 microns, and (C II) 158 microns. Comparison of the intensities and ratios of these lines with models of photodissociation regions (e.g., Tielens & Hollenbach 1985, ApJ, 344, 770) allows us to derive temperatures and densities of the primarily neutral atomic gas layers lying on the surfaces of UV-illuminated molecular gas. In general, the (C II) line arises ubiquitously throughout the molecular clouds while the (O I) lines are mainly confined to warm, dense gas (T is greater than 100 K, n is greater than 10(exp 4)/cu cm) near the sites of O and B stars. The distribution of (C II) in the star-forming clouds implies that the (C II) emission arises on the surfaces of molecular clumps throughout the clouds, rather than only at the boundary layer between molecular gas and H II regions.
    Keywords: ASTROPHYSICS
    Type: Astronomical Society of the Pacific, Airborne Astronomy Symposium on the Galactic Ecosystem: From Gas to Stars to Dust, Volume 73; p 91-92
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  • 55
    Publication Date: 2013-08-29
    Description: We present preliminary millimeter-wavelength images of the photodissociation region (PDR) in the Orion Bar, observed with the Berkeley- Illinois-Maryland array (BIMA). These new BIMA observations have attained 5 arc sec resolution in the J=l-O emission lines of HCO+ (formyl ion) and HCN (hydrogen cyanide). The results are compared with previous observations of the J=1-0 transition lines of (13)CO. We find that the HCO+ and HCN have different spatial distributions. HCN appears to lie primarily inside dense clumps of gas, which are defined by areas of intense (13)CO emission. However, the HCO+ emission appears to be only loosely associated with the surfaces of the gas clumps. We suggest that HCO+ abundance is enhanced by the presence of vibrationally excited H2 on the surfaces of dense clumps, and that the HCN abundance is attenuated by photo destruction outside the cores of dense clumps of gas.
    Keywords: ASTROPHYSICS
    Type: Astronomical Society of the Pacific, Airborne Astronomy Symposium on the Galactic Ecosystem: From Gas to Stars to Dust, Volume 73; p 87-90
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  • 56
    Publication Date: 2013-08-29
    Description: We present observations of the 34.815 micron (SiII) line and continuum emission from the inner few parsecs of the Galaxy obtained with the KAO Echelle Grating Spectrograph (KEGS) in June 1993. The SiII emission, which has been spectrally resolved at 64 km/s and spatially resolved at 10 arcsec, in kinematically consistent with the motions of ionized and neutral gas interior to the circumnuclear disk (CND). In addition, the emission in the (SiII) line as well as the continuum extends northward along the 'northern arm' past the inner edge of the CND. A peak in the (SiII) line/continuum ratio is observed at approx. 25 arcsec W and 75 arcsec N of Sgr A* with a large velocity dispersion. This may be an indication of dust destruction via cloud-cloud collisions.
    Keywords: ASTROPHYSICS
    Type: Astronomical Society of the Pacific, Airborne Astronomy Symposium on the Galactic Ecosystem: From Gas to Stars to Dust, Volume 73; p 469-476
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  • 57
    Publication Date: 2013-08-29
    Description: NGC 6334 is a nearby (1.7 kpc) giant molecular cloud which contains at least 7 distinct sites of massive star formation. Using the Far-infrared Imaging Fabry-Perot Interferometer (FIFI) on the Kuiper Airborne Observatory we have imaged this region in the FIR fine structure lines of O(0) and C(+). The line intensity ratios are compared with the predicted line ratios from the PDR models of Wolfire, Tielens and Hollenbach (1990) (hereafter WTH) to determine the gas density and UV field strength. The (O I) 63 mu m/ 145 mu m intensity ratio is at least a factor of 10 lower than predicted. We suggest that self-absorption by cooler foreground material suppresses the (O I) 63 mu m line. We have also mapped CO J = 2 to 1 emission with the Caltech Submillimeter Observatory (CSO). In general, we find an anticorrelation of (C II) and CO emission. Particularly striking is a (C II) peak which is not associated with any CO, FIR or radio continuum source. Consequently, there is no local source of hard UV radiation. Either (1) the (C II) peak is illuminated by a cluster of embedded B stars, which radiate enough soft UV photons to ionize carbon, or (2) the (C II) peak is illuminated by a distant O star.
    Keywords: ASTROPHYSICS
    Type: Astronomical Society of the Pacific, Airborne Astronomy Symposium on the Galactic Ecosystem: From Gas to Stars to Dust, Volume 73; p 83-86
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  • 58
    Publication Date: 2013-08-29
    Description: We summarize some of our KAO observations of far-infrared ionic fine-structure lines from Galactic H II regions, and discuss their interpretation.
    Keywords: ASTROPHYSICS
    Type: Astronomical Society of the Pacific, Airborne Astronomy Symposium on the Galactic Ecosystem: From Gas to Stars to Dust, Volume 73; p 53-58
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  • 59
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    Publication Date: 2013-08-29
    Description: The Interstellar Medium (ISM) forms an integral part of the lifecycle of stars and the galaxy. Stars are formed by gravitational contraction of interstellar clouds. Over their life, stars return much of their mass to the ISM through winds and supernova explosions, resulting in a slow enrichment in heavy elements. Understanding the origin and evolution of the ISM is a key problem within astrophysics. The KAO has made many important contributions to studies of the interstellar medium both on the macro and on the micro scale. In this overview, I will concentrate on two breakthroughs in the last decade in which KAO observations have played a major role: (1) the importance of large Polycyclic Aromatic Hydrocarbon (PAH) molecules for the ISM (section 3) and (2) the study of Photodissociation Regions (PDRs) as an analog for the diffuse ISM at large (section 4). Appropriately, the micro and macro problem are intricately interwoven in these problems. Finally, section 5 reviews the origin of the (CII) emission observed by COBE.
    Keywords: ASTROPHYSICS
    Type: Astronomical Society of the Pacific, Airborne Astronomy Symposium on the Galactic Ecosystem: From Gas to Stars to Dust, Volume 73; p 3-22
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  • 60
    Publication Date: 2013-08-29
    Description: Icy mantles on interstellar grains have been a topic of study in airborne astronomy. Recent laboratory analog studies of the yield of organic residue from UV photolyzed ices have shown that this mechanism can be the most significant source of complex reduced organic matter in the interstellar medium. However, the total yield is a function of the occurrence of heating events that evaporate the ice, i.e. T is greater than 130 K, and the mechanism for such events is debated. Recently, we proposed that the recombination of radicals in the ice does not need high temperature excursions and, instead, occurs during a structural transformation of water ice at temperatures in the range 38 - 68 K.
    Keywords: ASTROPHYSICS
    Type: Astronomical Society of the Pacific, Airborne Astronomy Symposium on the Galactic Ecosystem: From Gas to Stars to Dust, Volume 73; p 71-74
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  • 61
    Publication Date: 2013-08-29
    Description: This paper explains why far-infrared and sub-mm polarimetry should be used instead of background starlight polarimetry in order to map the magnetic field in the dense (greater than 10(exp 3) cm(exp -3)) regions of the interstellar medium. Results indicating the inadequacy of background starlight polarimetry, as well as the promise of far-infrared polarimetry, are discussed.
    Keywords: ASTROPHYSICS
    Type: Astronomical Society of the Pacific, Airborne Astronomy Symposium on the Galactic Ecosystem: From Gas to Stars to Dust, Volume 73; p 45-52
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  • 62
    Publication Date: 2013-08-29
    Description: We discuss measurements of the far-infrared (FIR) fine structure lines from (S III) (33 microns), (Si II) (35 microns), (O III) (51, 88 microns), (OI) (63 microns), (C II) (158 microns), and the adjacent continua in a strip crossing two of the thermal radio filaments in the Galactic Center 'Arch'. The near spatial coincidence of the line and continuum emission maxima with the radio filaments demonstrates that any excitation mechanism must account for both the line and continuum emission. The peak FIR luminosity and (O III) emission pose difficulties for collisional excitation models; photoionization of molecular cloud edges by a random distribution of stars is the most plausible mechanism proposed.
    Keywords: ASTROPHYSICS
    Type: Astronomical Society of the Pacific, Airborne Astronomy Symposium on the Galactic Ecosystem: From Gas to Stars to Dust, Volume 73; p 507-510
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  • 63
    Publication Date: 2013-08-29
    Description: The nucleus is a unique region in the Galactic ecosystem. It is also superb laboratory of modern astrophysics where astronomers can study, at unprecedented spatial resolution and across the entire electromagnetic spectrum, physical processes that may also happen at the cores of other galaxies. Infrared observations from the Kuiper Airborne Observatory have made important contributions to unraveling the mysteries of the Galactic nucleus and this review highlights some of these measurements, as well as recent results regarding the central parsec.
    Keywords: ASTROPHYSICS
    Type: Astronomical Society of the Pacific, Airborne Astronomy Symposium on the Galactic Ecosystem: From Gas to Stars to Dust, Volume 73; p 447-464
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  • 64
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    Publication Date: 2013-08-29
    Description: A survey is given of the accomplishments of airborne astronomy in solar-system science. They include identification of sulfuric acid in the clouds of Venus, establishment of Jupiter's internal heat source, discovery of water vapor and almost a dozen other molecules in Jupiter's atmosphere, important measurements of occultations of stars by Mars, Pluto, and Chiron, discovery of the rings of Uranus, and diagnosis of mineral composition on planetary surfaces.
    Keywords: ASTROPHYSICS
    Type: Astronomical Society of the Pacific, Airborne Astronomy Symposium on the Galactic Ecosystem: From Gas to Stars to Dust, Volume 73; p 281-284
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  • 65
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    Publication Date: 2013-08-29
    Description: This review outlines the observational properties of young stellar objects as they evolve from their birth within dense rotating molecular cores to fully-formed pre-main sequence stars. Current work suggests that most of the mass which ultimately comprises a fully-formed star is transferred from a flattened infalling envelope (of size approximately several thousand AU) through a circumstellar accretion disk to the stellar surface. We summarize current estimates for the duration of the envelope infall and disk accretion phases and discuss the implication of these timescales for the formation of stars of different mass and of planetary systems.
    Keywords: ASTROPHYSICS
    Type: Astronomical Society of the Pacific, Airborne Astronomy Symposium on the Galactic Ecosystem: From Gas to Stars to Dust, Volume 73; p 205-214
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  • 66
    Publication Date: 2013-08-29
    Description: Field stars provide an important means for probing undisturbed regions of molecular clouds where icy mantles are most likely to form. Combining observation of field stars with those of protostars provides a comparison of the extent of grain processing in photostellar environments. The Taurus dark cloud provides an ideal environment for the formation of icy mantles as it is free from shocks and bright internal sources of ultraviolet (UV) radiation. Earlier low-resolution observations of the Taurus cloud done by Whittet et al. (1989) showed that about 30 percent of the available CO is depleted on to the grains.
    Keywords: ASTROPHYSICS
    Type: Astronomical Society of the Pacific, Airborne Astronomy Symposium on the Galactic Ecosystem: From Gas to Stars to Dust, Volume 73; p 75-78
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  • 67
    Publication Date: 2013-08-29
    Description: We have investigated the charging processes which affect small carbonaceous dust grains and polycyclic aromatic hydrocarbons (PAH's). Because of their high abundance, interstellar PAH molecules can dominate the charge balance of the interstellar medium (ISM), which controls the heating and cooling interstellar gas and interstellar chemistry. We present the results of our model, which compare well with observations and suggest further applications to both laboratory measurements and data obtainable from the KAO.
    Keywords: ASTROPHYSICS
    Type: Astronomical Society of the Pacific, Airborne Astronomy Symposium on the Galactic Ecosystem: From Gas to Stars to Dust, Volume 73; p 59-62
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  • 68
    Publication Date: 2013-08-29
    Description: We present KAO observations of the CO J=9-8 and 12-11 lines in the C-star IRC+10216; these are the highest rotational transitions so far observed in any AGB star. A model is developed for the CO emission by IRC+10216 in all the observed CO rotational transitions.
    Keywords: ASTROPHYSICS
    Type: Astronomical Society of the Pacific, Airborne Astronomy Symposium on the Galactic Ecosystem: From Gas to Stars to Dust, Volume 73; p 433-436
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  • 69
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    Publication Date: 2013-08-29
    Description: Spectral imaging in the near-infrared of the central parsec of the Galaxy has revealed that a population of massive young stars resides in the core of our Galaxy. We suggest it has undergone a mild starburst.
    Keywords: ASTROPHYSICS
    Type: Astronomical Society of the Pacific, Airborne Astronomy Symposium on the Galactic Ecosystem: From Gas to Stars to Dust, Volume 73; p 465-468
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  • 70
    Publication Date: 2013-08-29
    Description: We computed optical and infrared light curves of the pulsating class of delayed detonation models for Type Ia supernovae (SNe Ia). It is demonstrated that observations of the IR light curves can be used to identify subluminous SNe Ia by testing whether secondary maxima occur in the IR. Our pulsating delayed detonation models are in agreement with current observations both for subluminous and normal bright SN Ia, namely SN1991bg, SN1992bo, and SN1992bc. Observations of molecular bands provide a test to distinguish whether strongly subluminous supernovae are a consequence of the pulsating mechanism occurring in a high-mass white dwarf (WD) or, alternatively, are formed by the helium detonation in a low-mass WD as was suggested by Woosley. In the latter case, no carbon is left after the explosion of low-mass WDs whereas a log of C/O-rich material is present in pulsating delayed detonation models.
    Keywords: ASTROPHYSICS
    Type: Astronomical Society of the Pacific, Airborne Astronomy Symposium on the Galactic Ecosystem: From Gas to Stars to Dust, Volume 73; p 441-444
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  • 71
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    Publication Date: 2013-08-29
    Description: Small inclusions (diameters ranging from 0.001 microns to 10 microns) of isotopically anomalous material within meteorites were almost certainly produced in mass-losing stars. These solid particles preserved their individual identities as they passed through the interstellar medium and the pre-solar nebular. The relationship between studies of meteorites and mass-losing red giants is explored.
    Keywords: ASTROPHYSICS
    Type: Astronomical Society of the Pacific, Airborne Astronomy Symposium on the Galactic Ecosystem: From Gas to Stars to Dust, Volume 73; p 359-364
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  • 72
    Publication Date: 2013-08-29
    Description: We present a preliminary analysis of far-IR polarimetric observations, which were made to study the magnetic field structure in the high-mass star formation regions of M42, NGC2024, and W3. These observations were made from the Kuiper Airborne Observatory (KAO), using the University of Chicago far-IR polarimeter, Stokes.
    Keywords: ASTROPHYSICS
    Type: Astronomical Society of the Pacific, Airborne Astronomy Symposium on the Galactic Ecosystem: From Gas to Stars to Dust, Volume 73; p 225-234
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  • 73
    Publication Date: 2013-08-29
    Description: We demonstrate that when there are gas density variations within a nebula, various line ratios used to determine electron density (Ne) can give different results. When there are non-constant density conditions, it is shown that by using one (average) Ne, significant, systematic biases may occur in the derived chemical abundance ratios. The abundance ratio of a heavy element (when a collisionally excited line is used) to ionized hydrogen may be subject to a large underestimate in the presence of density fluctuations. The more Ne-diagnostic observations made, the more reliable will be the deciphering of the actual Ne variation throughout a nebula.
    Keywords: ASTROPHYSICS
    Type: Astronomical Society of the Pacific, Airborne Astronomy Symposium on the Galactic Ecosystem: From Gas to Stars to Dust, Volume 73; p 115-118
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  • 74
    Publication Date: 2013-08-29
    Description: KAO observations of the 6.98 micron line of (Ar II), and KAO and ground-based observations of the 8.99 micron line of (Ar III) and the 12.8 micron line of (Ne II) are presented for a number of Galactic H II regions and planetary nebulae.
    Keywords: ASTROPHYSICS
    Type: Astronomical Society of the Pacific, Airborne Astronomy Symposium on the Galactic Ecosystem: From Gas to Stars to Dust, Volume 73; p 105-110
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  • 75
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    Publication Date: 2019-01-25
    Description: The author presents 16-65 micron spectra of late-type stars and proto-planetary nebulae (PPN) obtained with the Goddard 24-channel spectrophotometer from the Kuiper Airborne Observatory (KAO). The spectra of these objects contain most of the 9-13 known dust features, all discovered from the KAO, at wavelengths greater than 22 microns. The 8-100 micron spectra of a few representative objects are modeled with simple grains selected from a wide range of candidate solids. Hot sapphire is the most likely source of the 13 micron feature found in some M and MS star. Likely candidates for other features include ice, sulfides, and crystalline silicates. Also presented is a review of grain candidate materials for which optical properties in the far infrared have been measured, and a list of those for which measurements are needed.
    Keywords: ASTROPHYSICS
    Type: Astronomical Society of the Pacific, Airborne Astronomy Symposium on the Galactic Ecosystem: From Gas to Stars to Dust, Volume 73; p 395-396
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  • 76
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    Publication Date: 2019-06-28
    Description: Some p-mode frequencies and other observations were used to determine the mass, the age and the helium abundance of eta Bootes. It is shown how, by direct application, the p-mode frequencies and stellar seismological tools help in constraining the physical parameters of eta Boo. The existence of mode bumping is confirmed and it is discussed how it may be used to refine the estimate of the eta Boo's age. The effect of the OPAL equation of state on the p-mode frequencies is described.
    Keywords: ASTROPHYSICS
    Type: ESA, Proceedings of 4th SOHO on Helioseismology. Volume 2: Posters; p 555
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  • 77
    Publication Date: 2019-06-28
    Description: The infrared absorption feature near 2950(exp -1) (3.4 micron), characteristic of dust in the diffuse interstellar medium (ISM), is attributed to C-H stretching vibrations of aliphatic hydrocarbons. We show here that the strength of the band does not scale linearly with visual extinction everywhere, but instead increases more rapidly for objects near the center of the Galaxy, a behavior that parallels that of the Si-O stretching band due to silicate materials in the diffuse ISM. This implies that the grains responsible for the diffuse medium aliphatic C-H and silicate Si-O stretching bands are different from those responsible for much of the observed visual extinction. It also suggests that the distribution of the carbonaceous component of the diffuse ISM is not uniform throughout the Galaxy, but instead may increase in density toward the center of the Galaxy. The similar behavior of the C-H and Si-O stretching bands suggests that these two components may be coupled, perhaps in the form of silicate-core, organic-mantle grains. Several possible models of the distribution of this material are presented and it is demonstrated that the inner parts of the Galaxy has a carrier density that is 5 to 35 times higher than in the local ISM. Depending on the model used, the density of aliphatic material in the local ISM is found to be about 1 to 2 -CH3 groups m(exp -3) and about 2 to 5 -CH2- groups m(exp -3). These densities are consistent with the strengths of the 2955 and 2925 cm(exp -1) (3.4 micron) band being described by the relations A(sub nu)/tau(sub 2955 cm(exp -1)) = 270 +/- 40 and A(sub nu)/tau(sub 2925 cm(exp -1)) = 250 +/- 40 in the local diffuse ISM.
    Keywords: ASTROPHYSICS
    Type: NASA-CR-200003 , NAS 1.26:200003 , NIPS-96-07110
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  • 78
    Publication Date: 2019-06-28
    Description: The Liquid Xenon Coded Aperture Telescope (LXeCAT) and its capability to image astrophysical gamma-ray sources in the MeV region is described. The gamma-ray detector is a Liquid Xenon Time Projection Chamber (LXeTPC) triggered by the primary scintillation light. Effective background rejection is a direct consequence of the intrinsic three-dimensional imaging capability of the LXeTPC. Initial results with a 10 liter prototype confirm an energy resolution of 6% FWHM, a position resolution of 1 mm RMS and a light triggering efficiency higher than 90% for 1 MeV gamma-rays.
    Keywords: ASTROPHYSICS
    Type: NASA-CR-199796 , NAS 1.26:199796 , NIPS-95-06474
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  • 79
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    Publication Date: 2019-06-28
    Description: Seven comets have been observed from the Kuiper Airborne Observatory (KAO) in its twenty year history. Of these, comets p/Halley (1986 3) and Comet Wilson (1987 7) produced significant scientific results. Comet Halley was a bright and highly predictable comet that allowed a well-planned and coordinated observing program. Comet Wilson, on the other hand, was a dynamically new comet discovered only a few months before perihelion. In this paper we review the scientific discoveries made by the airborne program and the KAO on these comets, including the discovery of water, new structure in the silicate emission band, and a number of as yet unexplained spectral features.
    Keywords: ASTROPHYSICS
    Type: Astronomical Society of the Pacific, Airborne Astronomy Symposium on the Galactic Ecosystem: From Gas to Stars to Dust, Volume 73; p 297-328
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  • 80
    Publication Date: 2019-06-28
    Description: We have obtained new, high angular resolution far-infrared (FIR) maps (at 50 and 100 microns) of the star forming region Cepheus A and polarimetric images (1.65 and 2.2 microns) of the reflection nebulosity, IRS6, associated with this young stellar object. Our results are consistent with current star formation theories: a young stellar object surrounded by an infalling envelope with a characteristic density distribution of n(sub d)(r) proportional to r(exp -1.5), a circumstellar disk, and a cavity (R(sub i) approx. 0.07 pc) in which n(sub d) is constant, created by the dispersal of the initial dust cloud by a strong stellar wind.
    Keywords: ASTROPHYSICS
    Type: Astronomical Society of the Pacific, Airborne Astronomy Symposium on the Galactic Ecosystem: From Gas to Stars to Dust, Volume 73; p 263-266
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  • 81
    Publication Date: 2019-06-28
    Description: Far-infrared fine-structuze lines of compact H II regions can provide reliable abundances throughout the Galactic plane. We present here our most recent results, which once analyzed, will help to constrain models of the abundance gradient in our galaxy.
    Keywords: ASTROPHYSICS
    Type: Astronomical Society of the Pacific, Airborne Astronomy Symposium on the Galactic Ecosystem: From Gas to Stars to Dust, Volume 73; p 111-114
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  • 82
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    In:  Other Sources
    Publication Date: 2019-06-28
    Description: Gas in spiral galaxies cycles between the diffuse and dense phases as clouds collapse, form stars and are dispersed back into the ISM. Far infrared observations of continuum emission from interstellar dust and line emission from interstellar gas have revealed a wealth of information on the state of the ISM in galaxies of different morphological types. The analysis of these observations gives us information about the processes of star formation and about the evolution of the ISM. Star formation rates vary widely from galaxy to galaxy, with the rates in starburst galaxies being 10 - 100 times those in quiescent spiral galaxies. Far infrared spectroscopy of star-forming galaxies shows that the interstellar pressure increases with star formation rate. The structure of the interstellar medium in starburst galaxies is quite different from that of quiescent galaxies - much of the mass and volume are in HII regions and photodissociation regions. The size distribution of dust grains seems to depend on environment; small grains are abundant in the diffuse interstellar medium but not in dense molecular star forming regions. Quiescent spiral and elliptical galaxies contain a significant population of small grains, but starburst galaxies do not. Dwarf irregular galaxies also seem to contain few small grains; this may be the result of the higher UV flux in these galaxies. The star forming regions in dwarf irregulars also have a higher ratio of atomic to molecular gas than do those in the Galaxy. These results show that the ISM in galaxies of different morphological types reaches different equilibria, resulting in different modes of star formation and global galaxy evolution.
    Keywords: ASTROPHYSICS
    Type: Astronomical Society of the Pacific, Airborne Astronomy Symposium on the Galactic Ecosystem: From Gas to Stars to Dust, Volume 73; p 121-140
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    In:  Other Sources
    Publication Date: 2019-06-28
    Description: Measurements of the shapes, velocities, and intensities of FIR lines all help to probe the dynamics, physical associations, and excitation conditions of warm gas in molecular clouds. With this in mind, we have observed the J=9-8, 12-11,14-13, and 16-15 lines of (12)CO and the 158 micron line of C II in a number of positions in 4 selected clouds. The data were obtained with a laser heterodyne spectrometer aboard NASA's Kuiper Airborne Observatory. Line measurements at 0.6 km/s resolution allow us to resolve the profiles completely, and thereby to distinguish between UV-and shock-heating mechanisms for the high-excitation gas. For CO, the high-J linewidths lie in the range of 4-20 km/s (FWHM), similar to those observed for low-J (J less than 4) transitions in these sources. This correspondence suggests that the hotter gas (T = 200-600 K) is dynamically linked to the quiescent gas component, perhaps by association with the UV-heated peripheries of the numerous cloud clumps. Much of the C II emission is thought to emanate from these cloud peripheries, but the line profiles generally do not match those seen in CO. None of the observed sources show any evidence in high-J (12)CO emission for shock-excitation (i.e., linewidths greater than 30 km/s).
    Keywords: ASTROPHYSICS
    Type: Astronomical Society of the Pacific, Airborne Astronomy Symposium on the Galactic Ecosystem: From Gas to Stars to Dust, Volume 73; p 41-44
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  • 84
    Publication Date: 2019-06-28
    Description: We discuss airborne observations of rotational transitions of various hydride molecules in the interstellar medium, including H2O-18 and HCl. The detection of these transitions is now feasible with a new, sensitive submillimeter receiver which has been developed for the NASA Kuiper Airborne Observatory (KAO) over the past several years.
    Keywords: ASTROPHYSICS
    Type: Astronomical Society of the Pacific, Airborne Astronomy Symposium on the Galactic Ecosystem: From Gas to Stars to Dust, Volume 73; p 33-40
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