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  • ASTROPHYSICS  (293)
  • Lunar and Planetary Science and Exploration  (154)
  • 1
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    Extended CO(7-6) emission from warm gas in Orion (1993)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Results of a search for extended CO(7-6) line emission in the Orion A molecular cloud using the University of Texas submillimeter laser heterodyne receiver are presented. The large-scale distribution of quiescent CO(7-6) emission is mapped along a cut across the Trapezium cluster extending more than 13 arcmin (nearly 2 pc) in R.A. The receiver, observing method, and calibration techniques are described, and the CO(7-6) spectra and maps are presented. The physical parameters and energetics of the molecular gas are discussed. The findings are compared with observations of other high-luminosity star-forming regions.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 410; 1; p. 179-187.
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  • 2
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    IRAS asteroid families (1991)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The Infrared Astronomical Satellite (IRAS) sampled the entire asteroid population at wavelengths from 12 to 100 microns during its 1983 all sky survey. The IRAS Minor Planet Survey (IMPS) includes updated results for more recently numbered as well as other additional asteroids with reliable orbital elements. Albedos and diameters were derived from the observed thermal emission and assumed absolute visual magnitudes and then entered into the IMPS database at the Infrared Processing and Analysis Center (IPAC) for members of the Themis, Eos, Koronis and Maria asteroid families and compared with their visual colors. The IMPS results for the small (down to about 20 km) asteroids within these major families confirm trends previously noted for their larger members. Each of these dynamical families which are defined by their similar proper elements appears to have homogeneous physical properties.
    Keywords: ASTROPHYSICS
    Type: Lunar and Planetary Inst., Abstracts for the International Conference on Asteroids, Comets, Meteors 1991; p 225
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  • 3
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    Gamma-Ray Burst Arrival-Time Localizations: Simultaneous Observations by Mars Observer, Compton Observatory, and Ulysses (1996)
    In:  Other Sources
    Details
    Publication Date: 2018-06-08
    Description: Between October 4, 1992, and August 1, 1993, concurrent coverage by the Compton Gamma-Ray Observatory (CGRO), Mars Observer (MO), and Ulysses spacecraft, was obtained for 78 Gamma-Ray Bursts (GRBs).
    Keywords: Lunar and Planetary Science and Exploration
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  • 4
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    The Crust of the Moon as Seen by GRAIL (2013)
    In:  CASI
    Details
    Publication Date: 2019-07-23
    Description: High-resolution gravity data obtained from the dual Gravity Recovery and Interior Laboratory (GRAIL) spacecraft show that the bulk density of the Moon's highlands crust is 2550 kilograms per cubic meter, substantially lower than generally assumed. When combined with remote sensing and sample data, this density implies an average crustal porosity of 12% to depths of at least a few kilometers. Lateral variations in crustal porosity correlate with the largest impact basins, whereas lateral variations in crustal density correlate with crustal composition. The low-bulk crustal density allows construction of a global crustal thickness model that satisfies the Apollo seismic constraints, and with an average crustal thickness between 34 and 43 kilometers, the bulk refractory element composition of the Moon is not required to be enriched with respect to that of Earth.
    Keywords: Lunar and Planetary Science and Exploration
    Type: GSFC-E-DAA-TN6865 , Science (ISSN 0036-8075) (e-ISSN 1095-9203); 339; 6120; 671-675
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  • 5
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    Precession and nutation from joint analysis of radio interferometric and lunar laser ranging observations (1995)
    In:  Other Sources
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    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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  • 6
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    X-ray flares from runaway pair production in active galactic nuclei (1992)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: The hard X-ray spectrum of AGNs is nonthermal, probably arising from an electron-positron pair cascade, with some emission reflected off relatively cold matter. There has been interest in models on which protons are accelerated and create relativistic electrons on interaction with a local radiation field. It is shown here that a sufficient column density of protons can lead to runaway pair production: photons generated by the relativistic pairs are the targets for the protons to produce more pairs. This can produce X-ray fluxes with the characteristics observed in AGN. The model predicts the maximum ratio of luminosity to source size as well as their spectrum in the early phases. The same mechanism may also be able to create the knots of synchrotron-radiating pair plasma seen in sources such as 3C273.
    Keywords: ASTROPHYSICS
    Type: Nature (ISSN 0028-0836); 360; 6400; p. 135-137.
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  • 7
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    Diffuse Galactic low energy gamma ray continuum emission (1993)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: We investigate the origin of diffuse low-energy Galactic gamma-ray continuum down to about 30 keV. We calculate gamma-ray emission via bremsstrahlung and inverse Compton scattering by propagating an unbroken electron power law injection spectrum and employing a Galactic emmissivity model derived from COSB observations. To maintain the low energy electron population capable of producing the observed continuum via bremsstrahlung, a total power input of 4 x 10 exp 41 erg/s is required. This exceeds the total power supplied to the nuclear cosmic rays by about an order of magnitude.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics Supplement Series (ISSN 0365-0138); 97; 1; p. 145-148.
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  • 8
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    Mars Sample Return without Landing on the Surface (2000)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: Many in the science community want a Mars sample return in the near future, with the expectation that it will provide in-depth information, significantly beyond what we know from remote sensing, limited in-situ measurements, and work with Martian meteorites. Certainly, return of samples from the Moon resulted in major advances in our understanding of both the geologic history of our planetary satellite, and its relationship to Earth. Similar scientific insights would be expected from analyses of samples returned from Mars. Unfortunately, Mars-lander sample-return missions have been delayed, for the reason that NASA needs more time to review the complexities and risks associated with that type of mission. A traditional sample return entails a complex transfer-chain, including landing, collection, launch, rendezvous, and the return to Earth, as well as an evaluation of potential biological hazards involved with bringing pristine Martian organics to Earth. There are, however, means of returning scientifically-rich samples from Mars without landing on the surface. This paper discusses an approach for returning intact samples of surface dust, based on known instrument technology, without using an actual Martian lander.
    Keywords: Lunar and Planetary Science and Exploration
    Type: Concepts and Approaches for Mars Exploration; Part 1; 168-169; LPI-Contrib-1062-Pt-1
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  • 9
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    On two-dimensional relativistic stellar winds (1991)
    In:  CASI
    Details
    Publication Date: 2006-06-13
    Description: Stellar wind is of great interest, because many of the astrophysical systems possess wind like structures. For a long time only nonrelativistic winds have been studied. However, recently it was proposed by Kennel et al. that the relativistic pulsar wind with the plasma, consisting of electrons and positrons, can be responsible for the observed features of the Crab nebula. The study of Kennel et al. revealed the inconsistency of the assumption of the wind zero temperature with the observational data. It has been shown that only for high relativistic temperatures can high Mach numbers be reached, which allows the possibility of a shock formation. The analysis of Kennel et al. was extended into the 2-D case by using conventional magnetohydrodynamic equations for a relativistic plasma with an isotropic relativistic temperature. The state equation is assumed polytropic.
    Keywords: ASTROPHYSICS
    Type: NAS-NRC, High-Energy Astrophysics. American and Soviet Perspectives; p 108-111
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  • 10
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    Turbulization of shear flows in astrophysics (1991)
    In:  CASI
    Details
    Publication Date: 2006-06-13
    Description: The problem of instability in shear flows is treated in a number of works which present a global analysis of irrotational (potential) modes in a 2-D compressible shear flow, implying that, in the presence of reflecting boundaries, those modes can increase and that the characteristic time of the increase is several orders as high as the dynamic time in the medium. Due to the slowness of the increase of irrotational modes and to the problematic character of the theory's applicability for thin accretion disks, an attempt was made to develop an alternative theory of turbulization shear flows. It is quite contrary to the above theory. Instead of the global analysis, a local one is made far from the flow boundaries. Instead of irrotational perturbations, vortical ones are examined. Lastly, the medium is considered to be incompressible. The flow in the accretion disk can be modeled by a plane Couette flow, without regard for boundary conditions: it can be modeled by a plane shear flow in infinite incompressible fluid. According to this scenario, there is a critical perturbation level in the free shear flow. If the level of initial perturbations exceeds the critical one, the flow is turbulized.
    Keywords: ASTROPHYSICS
    Type: NAS-NRC, High-Energy Astrophysics. American and Soviet Perspectives; p 55-64
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