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  • Astrophysics  (2,384)
  • 2000-2004  (1,387)
  • 1995-1999  (997)
  • 1
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    Unknown
    In:  Other Sources
    Publication Date: 2019-08-28
    Description: A NASA spacecraft set for launch Nov. 17 is designed to help scientists determine the origin of gamma-ray bursts by pinpointing their sources in the sky and quickly focusing optical/ultraviolet and X-ray telescopes on them.
    Keywords: Astrophysics
    Type: Aviation Week and Space Technology; 161; 18; 33
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  • 2
    Publication Date: 2019-08-28
    Description: The measurements by neutron detectors on Odyssey have revealed two large poleward regions with large depression of flux of epithermal and high energy neutrons. The flux of neutrons from Mars is known to be produced by the bombardment of the surface layer by galactic cosmic rays. The leakage flux of epithermal and fast neutrons has regional variation by a factor of 10 over the surface of Mars. These variations are mainly produced by variations of hydrogen content in the shallow subsurface. On Mars hydrogen is associated with water. Therefore, the Northern and Southern depressions of neutron emission could be identified as permafrost regions with very high content of water ice. These regions are much larger than the residual polar caps, and could contain the major fraction of subsurface water ice. Here we present the results of HEND neutron data deconvolution for these regions and describe the similarities and differences between them.
    Keywords: Astrophysics
    Type: Lunar and Planetary Science XXXV: Special Session: Mars Climate Change; LPI-Contrib-1197
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  • 3
    Publication Date: 2019-08-28
    Description: It is the Policy of NASA s Office of Space Science to emphasize and encourage the addition of Participating Scientist Programs (PSP s) to broaden the scientific impact of missions. A Participating Scientist Program for the STARDUST Mission: STARDUST is the fourth Discovery mission, and it is the first sample return mission selected within the Discovery Program. The STARDUST Spacecraft will fly through the coma of comet PIwildt-2 in early January 2004, and return the samples to the Earth in January 2006. The Principal Investigator of the STARDUST mission, Dr. Donald Brownlee, has generously requested the implementation of a PSP for STARDUST in order to provide more community participation in the initial characterization and analysis of the samples from PIwildt-2. In particular participating scientists will fill out the membership of the Preliminary Examination Team (PET) called for in the original 1994 STARDUST proposal accepted by NASA in 1995. The work of the PET will be organized around major subdiscipline areas such as mineralogy and petrology, isotopic abundances, and elemental composition. There will be leaders for each of these areas, and also a number of team members within each. Support will be commensurate with the level of participation.
    Keywords: Astrophysics
    Type: Workshop on Cometary Dust in Astrophysics; 51; LPI-Contrib-1182
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  • 4
    Publication Date: 2019-08-28
    Description: The Astronomy and Physics Division at NASA Headquarters has an active and vibrant program in Laboratory Astrophysics. The objective of the program is to provide the spectroscopic data required by observers to analyze data from NASA space astronomy missions. The program also supports theoretical investigations to provide those spectroscopic parameters that cannot be obtained in the laboratory; simulate space environment to understand formation of certain molecules, dust grains and ices; and production of critically compiled databases of spectroscopic parameters. NASA annually solicits proposals, and utilizes the peer review process to select meritorious investigations for funding. As the mission of NASA evolves, new missions are launched, and old ones are terminated, the Laboratory Astrophysics program needs to evolve accordingly. Consequently, it is advantageous for NASA and the astronomical community to periodically conduct a dialog to assess the status of the program. This Workshop provides a forum for producers and users of laboratory data to get together and understand each others needs and limitations. A multi-wavelength approach enables a cross fertilization of ideas across wavelength bands.
    Keywords: Astrophysics
    Type: Proceedings of the NASA Laboratory Astrophysics Workshop; 15-16; NASA/CP-2002-211863
    Format: application/pdf
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  • 5
    Publication Date: 2019-08-28
    Description: As summarized in this pamphlet, some of the far-reaching underlying issues to be addressed include: What is the origin of the universe and its destiny; Why is the universe lumpy; How did the known structures of the universe evolve; How do galaxies evolve; How do massive black holes grow; How did the elemental composition of the universe evolve; What is the structure and behavior of matter in the extreme; and Is Einstein's general relativity theory right.
    Keywords: Astrophysics
    Type: NASA/TM-1998-208140 , NAS 1.15:208140 , PB98-121478
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  • 6
    Publication Date: 2019-08-27
    Description: We have compiled L' (3.4-4.1 microns) and M' (4.6- 4.8 microns) photometry of 63 single and binary M, L, and T dwarfs obtained at the United Kingdom Infrared Telescope using the Mauna Kea Observatory filter set. This compilation includes new L' measurements of eight L dwarfs and 13 T dwarfs and new M' measurements of seven L dwarfs, five T dwarfs, and the M1 dwarf Gl 229A. These new data increase by factors of 0. 6 and 1.6, respectively, the numbers of ultracool dwarfs T (sub eff) 〈/= 2400 K for which L' and M' measurements have been reported. We compute L(sub bol), BC(sub K), and T(sub eff) for 42 dwarfs whose flux-calibrated JHK spectra, L' photometry, and trigonometric parallaxes are available, and we estimate these quantities for nine other dwarfs whose parallaxes and flux-calibrated spectra have been obtained. BC(SUB K) is a well-behaved function of near-infrared spectral type with a dispersion of approx. 0.1 mag for types M6-T5 it is significantly more scattered for types T5-T9. T (sub eff) declines steeply and monotonically for types M6-L7 and T4-T9, but it is nearly constant at approx. 1450 K for types L7-T4 with assumed ages of approx. 3 Gyr. This constant T(sub eff) is evidenced by nearly unchanging values of L'-M' between types L6 and T3. It also supports recent models that attribute the changing near-infrared luminosities and spectral features across the L-T transition to the rapid migration, disruption, and/or thinning of condensate clouds over a narrow range of T(sub eff). The L' and M' luminosities of early-T dwarfs do not exhibit the pronounced humps or inflections previously noted in l through K bands, but insufficient data exist for types L6-T5 to assert that M(Sub L') and M(sub M') are strictly monotonic within this range of typew. We compare the observed K, L', and M' luminosities of L and T dwarfs in our sample with those predicted by precipitation-cloud-free models for varying surface gravities and sedimentation efficiencies.
    Keywords: Astrophysics
    Type: AD-A425483
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  • 7
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    Unknown
    In:  Other Sources
    Publication Date: 2019-08-27
    Description: The purpose of asteroseismology is not only to derive the internal structure of individual stars from their observed oscillation frequencies, but also to test and extend one's understanding of the physics of matter under the extremes of temperature, density, and pressure found in stellar interiors. In this review, the author hopes to point out what one can learn about the Sun by studying (delta) Scuti stars, as well as what one can learn about stars more massive or evolved than the Sun. He discusses some of the difficulties in theoretical approaches to asteroseismology for (delta) Scuti stars, using FG Vir, (delta) Scuti, and CD-24(degree) 7599 as examples.
    Keywords: Astrophysics
    Type: DE98-003371 , LA-UR-97-4362 , CONF-9708156 , New eyes to see inside the sun and stars; United States
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  • 8
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    In:  Other Sources
    Publication Date: 2019-08-26
    Description: The Space Studies Board is a unit of the NRC's Division on Engineering and Physical Sciences (DEPS), and it reports to the Division for oversight. DEPS is one of six major program units of the NRC through which the institution conducts its operations on behalf of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. Within DEPS there are a total of 14 boards that cover a broad range of physical science and engineering disciplines and mission areas. Members of the DEPS Committee on Engineering and Physical Sciences provide advice on Board membership and advise on proposed new projects to be undertaken by the Board or its committees. Every 3 years the DEPS Committee also reviews the overall operations of each of its boards. The last review of the SSB was in 2001. The Board meets three times per year to review the activities of its committees and task groups and to be briefed on and discuss major space policy issues. An internal executive committee composed of seven at-large members of the Board meets at least once a year and may convene via conference call at other times to plan for SSB activities and to advise the chair between meetings. All projects proposed to be conducted by standing committees or ad hoctask groups must first be reviewed and approved by the Board or its executive committee, and the Board monitors the progress of the projects throughout the course of the studies.
    Keywords: Astrophysics
    Type: PB2011-101832
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  • 9
    Publication Date: 2019-08-26
    Description: The N(2) Carroll-Yoshino (CY) c'(4) X (0,0) and (0,1) Rydberg bands between 95 and 99 nm were reported to be the most prominent EUV emission features in Voyager 1 ultraviolet spectrometer (UVS) airglow spectra from Titan's atmosphere. Although c'(4) is strongly excited by photoelectron impact, the (0,0) band is optically thick near peak production, so a multiple-scattering model is employed to calculate (0,v) nadir-viewing intensities. The model accounts for all known loss processes and quantifies the redistribution of photons to (0,v is greater than 0). Results show 7.6 R of (0,1) intensity, in agreement with reported observations (5-10 R), and 0.2 R of (0,0), in spectacular disagreement with reported observations (6-10 R). Nadir-viewing intensities of all other expected NI multiplets and N2 bands in the brightest portion of the EUV airglow spectrum (92.0-101.5 nm) are also calculated using photodissociative ionization of N(2) and photoelectron impact on N(2). It is found that NI multiplets and N(2) bands near (0,0) and unresolved by the UVS combine to produce 8.3 R, consistent with that reported for (0,0) and indicating that it was misidentified in previous analyses. The Ultraviolet Imaging Spectrograph (UVIS) on Cassini should unambiguously distinguish any (0,0) intensity from the brightest features nearby.
    Keywords: Astrophysics
    Type: AD-A529631 , Paper 1999JA000329 , Journal of Geophysical Research; 106; 3685-3689; No. A3
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  • 10
    Publication Date: 2019-08-17
    Description: We have obtained 1 1.7 and 17.9 micron images at the Keck I telescope of the circumstellar dust emission from L(sub 2) Pup, which is one of the nearest ( D = 61 pc) mass-losing, pulsating red giants that has a substantial infra-red excess. We propose that the star is losing mass at a rate of approx.3 x 10(exp -7) Solar Mass/yr. Given its relatively low luminosity (approx. 1500 Solar Luminosity), relatively high effective temperature (near 3400 K), relatively short period (approx. 140 days), and inferred gas outflow speed of 3.5 km/s, standard models for dust-driven mass loss do not apply. Instead, the wind may be driven by the stellar pulsations, with radiation pressure on dust being relatively unimportant. as described in some recent calculations. L(sub 2) Pup may serve as the prototype of this phase of stellar evolution, in which a star could lose approx. 15% of its initial main-sequence mass. Subject headings: circumstellar matter - stars: individual (L2 Puppis) - stars: mass loss
    Keywords: Astrophysics
    Type: The Astrophysical Journal (ISSN 0004-637X); 569; 2, Pt. 1; 964-974
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