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  • Astronomy  (533)
  • Earth model, also for more shallow analyses !
  • 2000-2004  (551)
  • 1980-1984
  • 1925-1929  (5)
  • 2001  (250)
  • 2000  (301)
  • 1926  (5)
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  • 2000-2004  (551)
  • 1980-1984
  • 1925-1929  (5)
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  • 1
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    In:  Physics of the Earth and Planetary Interiors, Heidelberg, Elsevier, vol. 127, no. 1-4, pp. 35-49, pp. 2164, (ISBN: 0-12-018847-3)
    Publication Date: 2001
    Keywords: Subduction zone ; Seismology ; Review article ; Earth model, also for more shallow analyses ! ; Reflectivity ; PEPI
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  • 2
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    In:  Eos, Trans., Am. Geophys. Un., Jena, Physica-Verlag, vol. 81, no. 19, pp. 210, pp. 2096, (ISSN: 1340-4202)
    Publication Date: 2000
    Keywords: Earth model, also for more shallow analyses ! ; Seismology ; Velocity depth profile ; double-prime
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  • 3
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    In:  Phys. Earth Plan. Int., Stuttgart, Schweizerbart'sche Verlagsbuchhandlung, vol. 119, no. 1-2, pp. 3-23, pp. 2271, (ISSN 0016-8548, ISBN 3-510-50045-8)
    Publication Date: 2000
    Keywords: Seismology ; Review article ; Project report/description ; Synthetic seismograms ; Clevede ; PEPI ; Earth model, also for more shallow analyses !
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  • 4
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    In:  Eos, Trans., Am. Geophys. Un., Berlin, Ges. f. Geowissenschaften e.V., vol. 81, no. 19, pp. 210, pp. L02309, (ISSN 0343-5164)
    Publication Date: 2000
    Keywords: Earth model, also for more shallow analyses ! ; Seismology ; Velocity depth profile ; double-prime
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  • 5
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    In:  Tectonophysics, Tokyo, Conseil de l'Europe, vol. 320, no. 3-4, pp. 175-194, pp. L01306, (ISSN: 1340-4202)
    Publication Date: 2000
    Keywords: Dynamic ; Tectonics ; Reflection seismics ; Refraction seismics ; EUROPROBE (Geol. and Geophys. in eastern Europe) ; Rheology ; Earth model, also for more shallow analyses ! ; Velocity depth profile ; Inelastic
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  • 6
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    In:  Eos, Trans., Am. Geophys. Un., Warszawa, Conseil de l'Europe, vol. 81, no. 19, pp. 210, pp. L19608, (ISBN: 0-12-018847-3)
    Publication Date: 2000
    Keywords: Earth model, also for more shallow analyses ! ; Seismology ; Velocity depth profile ; double-prime
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  • 7
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    In:  Zeitschrift für Geophysik, Jena, Gustav Fischer, vol. 2, no. 3, pp. 24-29, pp. L24306, (ISBN: 0534351875, 2nd edition)
    Publication Date: 1926
    Keywords: Earth model, also for more shallow analyses ! ; Seismology
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  • 8
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    In:  Meteorologische Zeitschrift, Jena, Gustav Fischer, vol. 43, no. 3, pp. 427-430, pp. L24306, (ISBN: 0534351875, 2nd edition)
    Publication Date: 1926
    Keywords: Earth model, also for more shallow analyses ! ; Meteorology
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  • 9
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    In:  Terra Nova, Oslo, Wiley, vol. 12, no. 3, pp. 102-108, pp. B08303, (ISSN: 1340-4202)
    Publication Date: 2000
    Keywords: Plate tectonics ; China ; Geol. aspects ; Volcanology ; Subduction zone ; Earth model, also for more shallow analyses ! ; Schaerer ; Scharer
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  • 10
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    In:  Pageoph, Basel, Inst. f. Geophys., Ruhr-Univ. Bochum, vol. 158, no. 1-2, pp. 79-103, pp. 1019, (ISSN: 1340-4202)
    Publication Date: 2001
    Keywords: Seismology ; Location ; Three dimensional ; Earth model, also for more shallow analyses ! ; Velocity depth profile ; Nuclear explosion ; PAG
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  • 11
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    In:  Pure and Applied Geophysics, Basel, Inst. f. Geophys., Ruhr-Univ. Bochum, vol. 158, no. 7, pp. 1121-1163, pp. 1009, (ISSN: 1340-4202)
    Publication Date: 2001
    Keywords: Nuclear explosion ; Lg-waves ; Tomography ; Earth model, also for more shallow analyses ! ; Velocity depth profile ; Deep seismic sounding (espec. cont. crust) ; Turkelli ; Tuerkelli ; Gurbuz ; Guerbuez ; PAG
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  • 12
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    In:  Physics of the Earth and Planetary Interiors, Luxembourg, Deutsche Geophys. Gesellschaft, vol. 123, no. 11, pp. 149-168, pp. 8045, (ISSN: 1340-4202)
    Publication Date: 2001
    Keywords: Earth model, also for more shallow analyses ! ; Velocity depth profile ; Three dimensional ; Surface waves ; Tomography ; interpolation ; volumetric ; visualization ; Seron ; PEPI
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  • 13
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    In:  Geophys. J. Int., Veldhoven, Kluwer, vol. 142, no. 2, pp. 351-360, pp. 2502, (ISSN: 1340-4202)
    Publication Date: 2000
    Keywords: Modelling ; Gravimetry, Gravitation ; Inelastic ; Rheology ; Earth model, also for more shallow analyses ! ; isostasy ; GJI
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  • 14
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    Bornträger
    In:  Professional Paper, Lehrbuch der Geophysik, Berlin, 6 + 1017 pp., Bornträger, vol. 3, no. VIIa, pp. 434-499, (ISBN: 3-540-23712-7)
    Publication Date: 1926
    Keywords: Seismology ; Earth model, also for more shallow analyses !
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  • 15
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    In:  Eos, Trans., Am. Geophys. Un. Trans. AGU, Luxembourg, Conseil de l'Europe, vol. 82, no. 25, pp. 273, 278 & 279, pp. 2214
    Publication Date: 2001
    Keywords: Gravimetry, Gravitation ; Earth model, also for more shallow analyses ! ; GeodesyY ; Plate tectonics ; hot ; spots
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  • 16
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    In:  DGG-Mitteilungen, Münster, Amer. Sc., vol. 78, no. 1, pp. 11-14, pp. 1228, (ISBN 0-471-26610-8)
    Publication Date: 2001
    Keywords: Earth model, also for more shallow analyses ! ; Geol. aspects ; Plate tectonics ; plume
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  • 17
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    In:  Natur und Museum, Jena, Gustav Fischer, vol. 56, no. 3, pp. 33-41, pp. L24306, (ISBN: 0534351875, 2nd edition)
    Publication Date: 1926
    Keywords: Handbook of geophysics ; Earth model, also for more shallow analyses !
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  • 18
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    In:  Die Umschau, Jena, Gustav Fischer, vol. 30, no. 3, pp. 265-268, pp. L24306, (ISBN: 0534351875, 2nd edition)
    Publication Date: 1926
    Keywords: Earth model, also for more shallow analyses ! ; Velocity depth profile
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  • 19
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    In:  Geophys. J. Int., Darmstadt, Wissenschaftliche Buchgesellschaft, vol. 142, no. 3, pp. 948-969, pp. B09404, (ISSN: 1340-4202)
    Publication Date: 2000
    Keywords: Earth model, also for more shallow analyses ! ; CRUST ; Anisotropy ; Electromagnetic methods/phenomena ; magneto-tellurics ; GJI
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  • 20
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    In:  Phys. Earth Plan. Int., Washington, D.C., AGU, vol. 119, no. 1-2, pp. 25-36, pp. 8011, (ISSN: 1340-4202)
    Publication Date: 2000
    Keywords: Modelling ; Synthetic seismograms ; Three dimensional ; Inhomogeneity ; PEPI ; Earth model, also for more shallow analyses ! ; Seismology
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  • 21
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    In:  Geophys. J. Int., Tokyo, Lawrence Livermore National Laboratory, vol. 141, no. 3, pp. F7-F11, pp. L18610, (ISSN: 1340-4202)
    Publication Date: 2000
    Keywords: Crustal deformation (cf. Earthquake precursor: deformation or strain) ; Inelastic ; Rheology ; Earthquake ; Earth model, also for more shallow analyses ! ; Modelling
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  • 22
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    In:  J. Geophys. Res., Kunming, China, 3-4, vol. 105, no. B2, pp. 2969-2980, pp. B05308, (ISSN: 1340-4202)
    Publication Date: 2000
    Keywords: Seismology ; Modelling ; Velocity depth profile ; Teleseismic events ; Earth model, also for more shallow analyses ! ; Plate tectonics ; Tectonics ; 7205 ; Seismology ; Continental ; crust ; (1242) ; 7260 ; Theory ; and ; modeling ; 8105 ; Tectonophysics ; Continental ; margins ; JGR ; sedimentary ; basins ; 8150 ; Plate ; boundary--general ; (3040)
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  • 23
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    In:  Rev. Geophys., Luxembourg, Conseil de l'Europe, vol. 38, no. 1, pp. 141-158, pp. 1484, (ISSN 0343-5164)
    Publication Date: 2000
    Keywords: Earth model, also for more shallow analyses ! ; Seismology ; 410 ; 660 ; earth mantle ; Subduction zone ; Waves ; Wave propagation ; 3630 ; Mineralogy ; petrology ; rock ; chemistry ; Experimental ; mineralogy ; and ; petrology ; 3939 ; Mineral ; physics ; Physical ; thermodynamics ; 7203 ; Seismology ; Body ; wave ; propagation ; 8124 ; Tectonophysics ; Earth's ; interior--composition ; and ; state ; (old ; 8105)
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  • 24
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    American Association for the Advancement of Science (AAAS)
    Publication Date: 2000-06-08
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Normile, D -- New York, N.Y. -- Science. 2000 May 19;288(5469):1165.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/10841732" target="_blank"〉PubMed〈/a〉
    Keywords: *Academies and Institutes/economics ; Animals ; Astronomical Phenomena ; Astronomy ; Chloroplasts/genetics ; Drosophila/genetics ; Interferometry ; *Molecular Biology/economics ; Physical Phenomena ; Physics ; *Research/economics ; Research Support as Topic ; Taiwan
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 25
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    American Association for the Advancement of Science (AAAS)
    Publication Date: 2001-12-26
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉New York, N.Y. -- Science. 2001 Dec 21;294(5551):2444.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/11752539" target="_blank"〉PubMed〈/a〉
    Keywords: Astronomical Phenomena ; Astronomy ; Biochemical Phenomena ; Biochemistry ; Computer Simulation ; Embryo, Mammalian/cytology ; Genetics, Medical ; Humans ; Microscopy, Electron ; Optics and Photonics ; Proteins/physiology ; Proteome ; *Research ; *Science ; Stem Cells
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 26
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    American Association for the Advancement of Science (AAAS)
    Publication Date: 2001-08-11
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Robert, F -- New York, N.Y. -- Science. 2001 Aug 10;293(5532):1056-8.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/11498566" target="_blank"〉PubMed〈/a〉
    Keywords: Astronomical Phenomena ; Astronomy ; Atmosphere ; Deuterium ; *Earth (Planet) ; *Evolution, Planetary ; *Hydrogen ; Mars ; *Meteoroids ; Silicates/chemistry ; *Water
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 27
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    American Association for the Advancement of Science (AAAS)
    Publication Date: 2001-10-13
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Malakoff, D -- New York, N.Y. -- Science. 2001 Oct 12;294(5541):292-3.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/11598283" target="_blank"〉PubMed〈/a〉
    Keywords: Astronomy ; Biological Evolution ; Ecology ; History, 20th Century ; Humans ; *Nobel Prize ; Psychology
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 28
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    American Association for the Advancement of Science (AAAS)
    Publication Date: 2001-02-24
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉New York, N.Y. -- Science. 2000 Dec 22;290(5500):2223.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/11188704" target="_blank"〉PubMed〈/a〉
    Keywords: Alzheimer Disease ; Astronomical Phenomena ; Astronomy ; Computing Methodologies ; Ecosystem ; Forecasting ; Humans ; Molecular Biology ; Poliomyelitis/epidemiology ; *Research/trends
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 29
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    American Association for the Advancement of Science (AAAS)
    Publication Date: 2000-08-05
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Muro, M -- New York, N.Y. -- Science. 2000 Jul 14;289(5477):228.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/10917838" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Arizona ; Astronomical Phenomena ; Astronomy ; Conservation of Natural Resources ; Population Dynamics ; *Sciuridae
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 30
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    American Association for the Advancement of Science (AAAS)
    Publication Date: 2000-01-15
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉New York, N.Y. -- Science. 1999 Dec 17;286(5448):2239-43.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/10636773" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Astronomical Phenomena ; Astronomy ; Eukaryotic Cells ; Genome ; Memory ; Nuclear Physics ; Photons ; *Research ; Ribosomes/chemistry/ultrastructure ; Sequence Analysis, DNA
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 31
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    American Association for the Advancement of Science (AAAS)
    Publication Date: 2001-02-24
    Description: Science recognizes nine other major discoveries on scales ranging from the cosmic to the quantum: Ribosome Revelations Fossil Find One Word--Organics New Cells for Old Water, Water, Everywhere Cosmic BOOMERANG Good Reception So NEAR ... Quantum Curiosities〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉New York, N.Y. -- Science. 2000 Dec 22;290(5500):2221-5.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/11188702" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Astronomical Phenomena ; Astronomy ; Cloning, Organism ; Electronics ; Humans ; Plastics ; Quantum Theory ; Receptors, Cytoplasmic and Nuclear/physiology ; *Research ; Ribosomes/chemistry/ultrastructure ; Stem Cells ; Water
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 32
    Publication Date: 2001-09-15
    Description: Recent advances in machine learning methods, along with successful applications across a wide variety of fields such as planetary science and bioinformatics, promise powerful new tools for practicing scientists. This viewpoint highlights some useful characteristics of modern machine learning methods and their relevance to scientific applications. We conclude with some speculations on near-term progress and promising directions.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Mjolsness, E -- DeCoste, D -- New York, N.Y. -- Science. 2001 Sep 14;293(5537):2051-5.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Machine Learning Systems Group, Jet Propulsion Laboratory/California Institute of Technology, Pasadena, CA, 91109, USA. mjolsness@jpl.nasa.gov〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/11557883" target="_blank"〉PubMed〈/a〉
    Keywords: Algorithms ; Animals ; *Artificial Intelligence ; Astronomical Phenomena ; Astronomy ; Cluster Analysis ; *Computational Biology ; Computer Simulation ; Gene Expression Profiling ; Gene Expression Regulation ; Image Processing, Computer-Assisted ; Neural Networks (Computer) ; Physical Phenomena ; Physics ; Robotics
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 33
    Publication Date: 2009-11-16
    Description: We present results of new ASCA observations of the low-luminosity AGN (LLAGN) NGC 4579 obtained in 1998 December 18 and 28, and we report on detection of variability of an iron K emission line. The X-ray luminosities in the 2-10 keV band for the two observations are nearly identical, L(sub X) approximately = 2 x 10(exp 4l) ergs/s, but they are approximately 35% larger than that measured in 1995 July by Terashima et al. (1998). An Fe K emission line is detected at 6.39 +/- 0.09 keV (source rest frame) which is lower than the line energy 6.73(sup +0.13, sub -0.12) keV in the 1995 observation. If we fit the Fe lines with a blend of two Gaussians centered at 6.4 keV and 6.73 KeV, the intensity of the 6.7 keV line decreased, while the intensity of the 6.4 keV line increased, within an interval of 3.5 years. This variability rules out thermal plasmas in the host galaxy as the origin of the ionized Fe line in this LLAGN. The detection and variability of the 6.4 keV line suggest that an optically thick standard accretion disk is present and subtends a large solid angle viewed from the nucleus at the Eddington ratio of L(sub Bol)/L(sub Eddington) approximately 2 x 10(exp -3) (Ho 1999). A broad disk-line profile is not clearly seen and the structure of the innermost part of accretion disk remains unclear.
    Keywords: Astronomy
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  • 34
    Publication Date: 2004-12-03
    Description: Ground-based differential photometry is limited to a precision of order 10(exp -3) because of atmospheric effects. A space-based photometer should be limited only by the inherent instrument precision and shot noise. Laboratory tests have shown that a precision of order 10-5 is achievable with commercially available charged coupled devices (CCDs). We have proposed to take this one step further by performing measurements at a telescope using a Wollaston prism as a beam splitter First-order atmospheric effects (e.g., extinction) will appear to be identical in the two images of each star formed by the prism and will be removed in the data analysis. This arrangement can determine the precision that is achievable under the influence of second-order atmospheric effects (e.g., variable point-spread function (PSF) from seeing). These telescopic observations will thus provide a lower limit to the precision that can be realized by a space-based differential photometer.
    Keywords: Astronomy
    Type: Third Workshop on Photometry; 95-102; NASA/CP-2000-209614
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  • 35
    Publication Date: 2004-12-03
    Description: Analysis of the images produced by the first version (V1) of the Vulcan photometer indicated that two major sources of noise were sky brightness and image motion. To reduce the effect of the sky brightness, a second version (V2) with a longer focal length and a larger format detector was developed and tested. The first version consisted of 15-centimeter (cm) focal length, F/1.5 Aerojet Delft reconnaissance lens, and a 2048 x 2048 format front-illuminated charged coupled device (CCD) with 9 microns micropixels (Mpixels). The second version used a 30-cm focal length, F/2.5 Kodak AeroEktar lens, and a 4096 x 4096 format CCD with 9 micro pixels. Both have a 49-square-degree field of view (FOV) but the area of the sky subtended by each pixel in the V2 version is one-fourth that of the V1 version. This modification substantially reduces the shot noise due to the sky background and allows fainter stars to be monitored for planetary transits. To remove the data gap and consequent signal-level change caused by flipping the photometer around the declination axis and to reduce image movement on the detector, several other modifications were incorporated. These include modifying the mount and stiffening the photometer and autoguider structures to reduce flexure. This paper compares the performance characteristics of each photometer and discusses tests to identify sources of systematic noise.
    Keywords: Astronomy
    Type: Third Workshop on Photometry; 63-70; NASA/CP-2000-209614
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  • 36
    Publication Date: 2004-12-03
    Description: This report summarizes the technical parameters and the technical staff of the Very Long Base Interferometry (VLBI) system at the fundamental station Goddard Geophysical and Astronomical Observatory (GGAO). It also gives an overview about the VLBI activities during the previous year. The outlook lists the outstanding tasks to improve the performance of GGAO.
    Keywords: Astronomy
    Type: International VLBI Service for Geodesy and Astrometry; 81-82; NASA/TP-2001-209979
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  • 37
    Publication Date: 2011-08-23
    Description: We present X-ray emission-line equivalent width images of the bright Galactic supernova remnant Cassiopeia A for the elements Si, S, Ar, Ca, and Fe using a 50,000 s observation with the Advanced CCD Imaging Spectrometer on the Chandra X-Ray Observatory. The images essentially map the bulk of detectable ejecta of these elements over a wide range of surface brightnesses and show morphologies distinctly different from that of the broadband X-ray emission and the 4-6 keV continuum emission. The Si, S, Ar, and Ca maps, while different in turn from those of Fe, are similar to the distribution of fast optical ejecta knots in that they clearly delineate the X-ray counterpart of the northeast optical jet. Low surface brightness regions just outside the bright shell in the north and west are also shown to have strong line emission. The strong Fe emission is exterior to that of other elements in the east, as previously noted, but is generally coincident elsewhere. The projected interior has relatively little emission traced by high line equivalent widths.
    Keywords: Astronomy
    Type: The Astrophysical Journal; Volume 537; L119-L122
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  • 38
    Publication Date: 2011-08-23
    Description: We report the discovery in archival Rossi X-Ray Timing Explorer data of a approx. 40 Hz quasi-periodic oscillation QPO) in the hard X-ray flux from the Galactic microquasar GRS 1915+105. The QPO is detected only in the hard X-ray band above approx. 13 keV and was discovered in observations in which the previously known 67 Hz QPO is present. The 40 Hz QPO has a typical rms amplitude of approx. 2% in the 13-27 keV band and a width of approx. 5.5 Hz (FWHM). We show that the 67 and 40 Hz QPOs are detected in the same observations in 1997 July and November. However, the QPO is not detected in observations from 1996 April, May, and June in which the 67 Hz QPO was first discovered. The frequency of the 67 Hz QPO is significantly higher in the 1997 observations by about 5% compared with the 1996 data. The identification of the 40 Hz QPO makes GRS 1915 + 105 the second black hole binary to show a pair of simultaneous high-frequency QPOs (the other being GRO J1655-40). The similarities between the properties of the 67 Hz QPO in GRS 1915+105 and the recently discovered 450 Hz QPO in GRO J1655-40 suggest that the pairs of frequencies in these systems may be produced by the same physical mechanism, with the frequency differences between the two being likely due to different black hole masses in the two systems. We discuss the implications of our result for the mass and spin of GRS 1915+105 as well as for models of X-ray variability in black holes and neutron stars.
    Keywords: Astronomy
    Type: Astronomical Journal; Volume 554; L169-L172
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  • 39
    Publication Date: 2011-08-23
    Description: We observe a slow-onset quiet-region filament eruption with the Extreme Ultraviolet Imaging Telescope (EIT) on the Solar Heliospheric Observatory (SOHO) and the Soft X-ray Telescope (SXT) on Yohkoh. This event occurred on 1999 April 18 and was likely the origin of a coronal mass ejection detected by SOHO at 08:30 UT on that day. In the EIT observation, one-half of the filament shows two stages of evolution: stage 1 is a slow, roughly constant upward movement at approximately 1 km/s lasting approximately 0.5 hr, and stage 2 is a rapid upward eruption at approximately 16 km/s occurring just before the filament disappears into interplanetary space. The other half of the filament shows little motion along the line of sight during the time of stage 1 but erupts along with the rest of the filament during stage 2. There is no obvious emission from the filament in the SXT observation until stage 2; at that time, an arcade of EUV and soft X-ray loops forms first at the central location of the filament and then expands outward along the length of the filament channel. A plot of EUV intensity versus time of the central portion of the filament (where the postflare loops initially form) shows a flat profile during stage 1 and a rapid upturn after the start of stage 2. This light curve is delayed from what would be expected if 'tether-cutting' reconnection in the core of the erupting region were responsible for the initiation of the eruption. Rather, these observations suggest that a loss of stability of the magnetic field holding the filament initiates the eruption, with reconnection in the core region occurring only as a by-product.
    Keywords: Astronomy
    Type: Astrophysical Journal; Volume 561; L219-L222
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  • 40
    Publication Date: 2011-08-23
    Description: The magnetic flux content of the Jovian magnetosphere is set by the internal dynamo, but those magnetic field lines are constantly being loaded by heavy ions at the orbit of lo and dragged inexorably outward by the centrifugal force. Vasyliunas has proposed a steady state reconnecting magnetospheric model that sheds plasma islands of zero net magnetic flux and returns nearly empty flux tubes to the inner magnetosphere. The Galileo observations indicate that beyond 40 Rj the current sheet begins to tear and beyond 50 Rj on the nightside explosively reconnects as the tearing site reaches the low density lobe region above and below the current sheet. Small events occur irregularly but on average about every 4 hours and large events about once a day. The magnetic flux reconnected in such events amounts up to about 70,000 Webers/sec and is sufficient to return the outwardly convected magnetic flux to the inner magnetosphere. Since this process releases plasmoids into the jovian tail, as do terrestrial substorms; since this process involves explosive reconnection across the current sheet on the nightside of the planet, as do terrestrial substorms; and since the process is a key in closing the circulation pattern of the magnetic and plasma flux, as it is in terrestrial substorms; we refer to these events as jovian substorms.
    Keywords: Astronomy
    Type: Advanced Space Research (ISSN 0273-1177); Volume 26; No. 10; 1499-1504
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  • 41
    Publication Date: 2011-08-24
    Description: No abstract available
    Keywords: Astronomy
    Type: Stellar Astrophysics, Proceedings of the Pacific; 267
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  • 42
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    In:  CASI
    Publication Date: 2013-08-31
    Description: The Space Interferometry Mission (SIM) is a space-based 10 m baseline Michelson interferometer. Planned for launch in 2005 aboard a Delta III launch vehicle, or equivalent, its primary objective is to measure the positions of stars and other celestial objects with an unprecedented accuracy of 4 micro arc seconds. With such an instrument, tremendous advancement can be expected in our understanding of stellar and galactic dynamics. Using triangulation from opposite sides of the orbit around the sun (i.e. by using parallax) one can measure the distance to any observable object in our galaxy. By directly measuring the orbital wobble of nearby stars, the mass and orbit of planets can be determined over a wide range of parameters. The distribution of velocity within nearby galaxies will be measurable. Observations of these and other objects will improve the calibration of distance estimators by more than an order of magnitude. This will permit a much better determination of the Hubble Constant as well as improving our overall understanding of the evolution of the universe. SIM has undergone several transformations, especially over the past year and a half since the start of Phase A. During this phase of a project, it is desirable to perform system-level trade studies, so the substantial evolution of the design that has occurred is quite appropriate. Part of the trade-off process has addressed two major underlying architectures: SIM Classic; and Son of SIM. The difference between these two architectures is related to the overall arrangement of the optical elements and the associated metrology system. Several different configurations have been developed for each architecture. Each configuration is the result of design choices that are influenced by many competing considerations. Some of the more important aspects will be discussed. The Space Interferometry Mission has some extremely challenging goals: millikelvin thermal stability, nanometer stabilization of optics, picometer measurement of wavefront, and others. In order to meet these goals, a significant amount of technological development is required. Although there has been a program operating for about a decade developing technologies specifically to address the challenges of space-based interferometry, there still remains a tremendous effort to achieve the incredible accuracy required of SIM. The projected viability of some of these areas has influenced design choices during the evolution of the many configurations that have been developed. For instance, the perceived complexity of the IR laser metrology system used to measure and control the positions of key optical elements was the strongest discriminator between the two architectures, and led to a decision to select SOS rather than Classic in early 1998. More recently, an appreciation of the sensitivity to beam-walk within the SOS architecture is forcing a reconsideration of that decision. At the time of submission of this abstract, there is some hope that a full-aperture metrology system may alleviate this issue. In addition to describing the current configuration of SIM, the influence of a few selected areas on the evolution of the configuration will be discussed.
    Keywords: Astronomy
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  • 43
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    In:  CASI
    Publication Date: 2013-08-31
    Description: The Trans-Pacific Astronomy Experiment is Phase 2 of the Trans-Pacific High Data Rate Satcom Experiments following the Trans-Pacific High Definition Video Experiment. It is a part of the Global Information Infrastructure-Global Interoperability for Broadband Networks Project (GII-GIBN). Provides global information infrastructure involving broadband satellites and terrestrial networks and access to information by anyone, anywhere, at any time. Collaboration of government, industry, and academic organizations demonstrate the use of broadband satellite links in a global information infrastructure with emphasis on astronomical observations, collaborative discussions and distance learning.
    Keywords: Astronomy
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  • 44
    Publication Date: 2013-08-29
    Description: Hot subluminous stars lying up to 0.7 mag below the extreme horizontal branch (EHB) are found in the ultraviolet (UV) color magnitude diagrams of both (omega) Cen and NGC 2808. In order to explore the evolutionary status of these subluminous stars, we have evolved a set of low-mass stars continuously from the main sequence through the helium-core flash to the HB (horizontal branch) for a wide range in the mass loss along the red-giant branch (RGB). Stars with the largest mass loss evolve off the RGB to high effective temperatures before igniting helium in their cores. Our results indicate that the subluminous EHB stars, as well as the gap within the EHB of NGC 2808, can be explained if these stars undergo a late helium-core flash while descending the white-dwarf cooling curve. Under these conditions the convection zone produced by the helium flash will penetrate into the stellar envelope, thereby mixing most, if not all, of the envelope hydrogen into the hot helium-burning interior, where it is rapidly consumed. This phenomenon is analogous to the 'born-again' scenario for producing hydrogen-deficient stars following a very late helium-shell flash. This 'flash mixing' of the stellar envelope greatly enhances the envelope helium and carbon abundances and, as a result, leads to a discontinuous jump in the HB effective temperature. We argue that the EHB gap in NGC 2808 is associated with this theoretically predicted dichotomy in the HB morphology. Using new helium- and carbon-rich stellar atmospheres, we show that these changes in the envelope abundances of the flash-mixed stars will suppress the UV flux by the amount needed to explain the hot subluminous EHB stars in (omega) Cen and NGC 2808. Moreover, we demonstrate that models without flash mixing lie, at most, only approximately 0.1 mag below the EHB, and hence fail to explain the observations. Flash mixing may also provide a new evolutionary channel for producing the high gravity, helium-rich sdO and sdB stars.
    Keywords: Astronomy
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  • 45
    Publication Date: 2013-08-29
    Description: In a previous paper we point out that the X-ray luminosity L(sub x) of a galaxy is driven by the evolution of its X-ray binary population and that the profile of L(sub x) with redshift can both serve as a diagnostic probe of the Star Formation Rate (SFR) profile and constrain evolutionary models for X-ray binaries. We update our previous work using a suite of more recently developed SFR profiles that span the currently plausible range. The first Chandra deep imaging results on L(sub x)-evolution are beginning to probe the SFR profile of bright spirals and the early results are consistent with predictions based on current SFR models. Using these new SFR profiles the resolution of the "birthrate problem" of lowmass X-ray binaries (LMXBs) and recycled, millisecond pulsars in terms of an evolving global SFR is more complete. We also discuss the possible impact of the variations in the SFR profile of individual galaxies.
    Keywords: Astronomy
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  • 46
    Publication Date: 2013-08-29
    Description: Using the Chandra X-ray Observatory we have discovered a second bright X-ray source in the globular cluster M15 that is 2.7" to the west of AC211, the previously known low mass X-ray binary (LMXB) in this system. Prior to the 0.5" imaging capability of Chandra this second source could not have been resolved from AC211. The luminosity and spectrum of this new source, which we call M15-X2, are consistent with it also being a LMXB system. This is the first time that two LMXBs have been seen to be simultaneously active in a globular cluster. The new source, M15-X2, is coincident with a 18th U magnitude very blue star. The discovery of a second LMXB in M15 clears up a long standing puzzle where the X-ray and optical properties of AC211 appear consistent with the central source being hidden behind an accretion disk corona, and yet also showed a luminous X-ray burst suggesting the neutron star is directly visible. This discovery suggests instead that the X-ray burst did not come from AC211, but rather from the newly discovered X-ray source. We discuss the implications of this discovery for X-ray observations of globular clusters in nearby galaxies.
    Keywords: Astronomy
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  • 47
    Publication Date: 2013-08-29
    Description: Eta Carinae may be the most massive and luminous star in the Galaxy and is suspected to be a massive, colliding wind binary system. The CHANDRA X-ray observatory has obtained a calibrated, high-resolution X-ray spectrum of the star uncontaminated by the nearby extended soft X-ray emission. Our 89 ksec CHANDRA observation with the High Energy Transmission Grating Spectrometer (HETGS) shows that the hot gas near the star is non-isothermal. The temperature distribution may represent the emission on either side of the colliding wind bow shock, effectively 'resolving' the shock. If so, the pre-shock wind velocities are approximately 700 and 1800 km/s in our analysis, and these velocities may be interpreted as the terminal velocities of the winds from 71 Carinae and from the hidden companion star. The forbidden-to-intercombination line ratios for the He-like ions of S, Si, and Fe are large, indicating that the line forming region lies far from the stellar photosphere. The iron fluorescent line at 1.93 angstroms, first detected by ASCA, is clearly resolved from the thermal iron line in the CHANDRA grating spectrum. The Fe fluorescent line is weaker in our CHANDRA observation than in any of the ASCA spectra. The CHANDRA observation also provides the first high-time resolution lightcurve of the uncontaminated stellar X-ray emission from 77 Carinae and shows that there is no significant, coherent variability during the CHANDRA observation. The 77 Carinae CHANDRA grating spectrum is unlike recently published X-ray grating spectra of single massive stars in significant ways and is generally consistent with colliding wind emission in a massive binary.
    Keywords: Astronomy
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  • 48
    Publication Date: 2013-08-29
    Description: The Next Generation Space Telescope (NGST), planned for launch in 2009, will be an 8-m class radiatively cooled infrared telescope at the Lagrange point L2. It will cover the wavelength range from 0.6 to 28 microns with cameras and spectrometers, to observe the first luminous objects after the Big Bang, and the formation, growth, clustering, and evolution of galaxies, stars, and protoplanetary clouds, leading to better understanding of our own Origins. It will seek evidence of the cosmic dark matter through its gravitational effects. With an aperture three times greater than the Hubble Space Telescope, it will provide extraordinary advances in capabilities and enable the discovery of many new phenomena. It is a joint project of the NASA, ESA, and CSA, and scientific operations will be provided by the Space Telescope Science Institute.
    Keywords: Astronomy
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  • 49
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    In:  CASI
    Publication Date: 2013-08-29
    Description: Astronomers study light and basically, almost everything we know about the universe has been figured out through the study of light gathered by telescopes on the earth, in the earth's atmosphere, and in space. This light comes in many different colors, the sum of which comprises what is commonly I known as the electromagnetic (EM) spectrum. Unfortunately, the earth's atmosphere blocks almost all of wavelengths in the EM spectrum. Only the visible (400-700 mn) and radio (approx. 1-150 m) "windows" are accessible from the ground, and thus have the longest observational "history." These early restrictions on the observational astronomer also gave rise to classifying "kinds" of astronomy based on their respective EM portion, such as the term "radio astronomy."
    Keywords: Astronomy
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  • 50
    Publication Date: 2013-08-29
    Description: Nexus was a technology demonstrator project that was designed to bridge from the Hubble Space Telescope (HST) to its successor, the Next Generation Space Telescope (NGST). This paper focuses on the process used in designing the ground segment for Nexus and the lessons learned in its development. Ground station cost drivers were: (1) Contact time, (2) Cost of transporting data between the ground stations and control center, and (3) Cost savings via ground automation. We found that reducing the communication requirement in just the first 100 days could have reduced the total ground station cost by 40%. Contact time cost dwarfed the cost trade between automation development and off-shift operations personnel. Real-time Telemetry and Control (T&C) system analysis was divided into: (1) Potential reuse of the Nexus real-time (T&C) system for NGST, (2) Feasibility of using a 'Finite State-Based Modeling' product, and (3) Selecting a Commercial Off the Shelf (COTS) versus Government Off The Shelf (GOTS) products. We found that each of the products evaluated in detail (ASIST, EPOCH 2000, and ITOS) could adequately support basic mission requirements. Lessons learned were: (1) Include operations at the beginning of the mission, and (2) Develop an operations concept as soon as possible.
    Keywords: Astronomy
    Type: Reducing Cost of S/C Ground Systems and Optics; United States
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  • 51
    Publication Date: 2013-08-29
    Description: With the realization of NASA's era of great observatories, there are now more than three space-based telescopes operating in different wavebands. This situation provides astronomers with a unique opportunity to simultaneously observe with multiple observatories. Yet scheduling multiple observatories simultaneously is highly inefficient when compared to observations using only one single observatory. Thus, programs using multiple observatories are limited not due to scientific restrictions, but due to operational inefficiencies. At present, multi-observatory programs are conducted by submitting observing proposals separately to each concerned observatory. To assure that the proposed observations can be scheduled, each observatory's staff has to check that the observations are valid and meet all the constraints for their own observatory; in addition, they have to verify that the observations satisfy the constraints of the other observatories. Thus, coordinated observations require painstaking manual collaboration among the observatory staff at each observatory. Due to the lack of automated tools for coordinated observations, this process is time consuming, error-prone, and the outcome of the requests is not certain until the very end. To increase observatory operations efficiency, such manpower intensive processes need to undergo re-engineering. To overcome this critical deficiency, Goddard Space Flight Center's Advanced Architectures and Automation Branch is developing a prototype effort called the Visual Observation Layout Tool (VOLT). The main objective of the VOLT project is to provide visual tools to help automate the planning of coordinated observations by multiple astronomical observatories, as well as to increase the scheduling probability of all observations.
    Keywords: Astronomy
    Type: ADASS Conference; Boston, MA; United States
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  • 52
    Publication Date: 2013-08-29
    Description: We present RXTE monitoring observations of the Seyfert 2 galaxy Mrk 348 spanning a 6 month period. The time-averaged spectrum in the 3-20 keV band shows many features characteristic of a Compton-thin Seyfert 2 galaxy, namely a hard underlying power-law continuum (Gamma approximately equal 1.8) with heavy soft X-ray absorption (N(sub H) approximately 10(exp 23)/sq cm) plus measurable iron K.alpha emission (equivalent width approximately 100 eV) and, at high energy, evidence for a reflection component (R approximately 〈 1). During the first half of the monitoring period the X-ray continuum flux from Mrk 348 remained relatively steady. However this was followed by a significant brightening of the source (by roughly a factor of 4) with the fastest change corresponding to a doubling of its X-ray flux on a timescale of about 20 days. The flux increase was accompanied by a marked softening of X-ray spectrum most likely attributable to a factor approximately 3 decline in the intrinsic line-of-sight column density. In contrast the iron K.alpha line and the reflection components showed no evidence of variability. These observations suggest a scenario in which the central X-ray source is surrounded by a patchy distribution of absorbing material located within about a light-week of the nucleus of Mrk 348. The random movement of individual clouds within the absorbing screen, across our line of sight, produces substantial temporal variations in the measured column density on timescales of weeks to months and gives rise to the observed X-ray spectral variability. However, as viewed from the nucleus the global coverage and typical thickness of the cloud layer remains relatively constant.
    Keywords: Astronomy
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  • 53
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    In:  CASI
    Publication Date: 2013-08-29
    Description: Life as an astronomer has taken me to view eclipses of the Sun from the Gaspe' Peninsula to the Pacific Ocean and the China and Coral Seas, and to observe the stars at observatories across the USA and as far south as Chile. I've also enjoyed working with NASA's telescopes in space, including the Hubble Space Telescope and the International Ultraviolet Explorer. It seems funny to reflect that it all began in the Sixth Grade by a fluke - the consequence of a hoax letter whose author I never identified.
    Keywords: Astronomy
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  • 54
    Publication Date: 2013-08-29
    Description: The Gamma Ray Large Area Space Telescope (GLAST) Large Area Telescope (LAT) is a pair-production high-energy (greater than 20 MeV) gamma-ray telescope being built by an international partnership of astrophysicists and particle physicists for a satellite launch in 2006, designed to study a wide variety of high-energy astrophysical phenomena. As part of the development effort, the collaboration has built a Balloon Flight Engineering Model (BFEM) for flight on a high-altitude scientific balloon. The BFEM is approximately the size of one of the 16 GLAST-LAT towers and contains all the components of the full instrument: plastic scintillator anticoincidence system (ACD), high-Z foil/Si strip pair-conversion tracker (TKR), CsI hodoscopic calorimeter (CAL), triggering and data acquisition electronics (DAQ), commanding system, power distribution, telemetry, real-time data display, and ground data processing system. The principal goal of the balloon flight was to demonstrate the performance of this instrument configuration under conditions similar to those expected in orbit. Results from a balloon flight from Palestine, Texas, on August 4, 2001, show that the BFEM successfully obtained gamma-ray data in this high-background environment.
    Keywords: Astronomy
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  • 55
    Publication Date: 2013-08-29
    Description: As funding, for astronomy dwindles and the competition for observation time heats up, more astronomers may turn to balloons. Far above the Keck telescope on Hawaii's Mauna Kea, higher still than the hostile snowcapped peaks of Mt. Everest, there exists a 40-kilometer summit that will place their telescopes above 99% of the atmosphere. With the prospect of 100-day and even 1,000-day balloons, the climb to the summit is more and more tempting. Surely, given enough cash, most astronomers would opt for a lunar base or a platform beyond the Earth. Until then, many seem happy to settle for a stratospheric mountaintop.
    Keywords: Astronomy
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  • 56
    Publication Date: 2013-08-29
    Description: We report an observation by the Chandra X-ray Observatory of 4U2127+119, the X-ray source identified with the globular cluster M15. The Chandra observation reveals that 4U2127+119 is in fact two bright sources, separated by 2.7". One source is associated with AC21 1, the previously identified optical counterpart to 4U2127+119, a low mass X-ray binary (LMXB). The second source, M15-X2, is coincident with a 19th U magnitude blue star that is 3.3" from the cluster core. The Chandra count rate of M15-X2 is 2.5 times higher than that of AC211. Prior to the 0.5" imaging capability of Chandra the presence of two so closely separated bright sources would not have been resolved, The optical counterpart, X-ray luminosity and spectrum of M15-X2 are consistent with it also being an LMXB system. This is the first time that two LMXBS have been seen to be simultaneously active in a globular cluster. The discovery of a second active LMXB in M15 solves a long standing puzzle where the properties of AC211 appear consistent with it being dominated by an extended accretion disk corona, and yet 4U2127+119 also shows luminous X-ray bursts requiring that the neutron star be directly visible. The resolution of 4U2127+119 into two sources suggests that the X-ray bursts did not come from AC211, but rather from M15X2. We discuss the implications of this discovery for understanding the origin and evolution of LMXBs in GCs as well as X-ray observations of globular clusters in nearby galaxies.
    Keywords: Astronomy
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  • 57
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    In:  CASI
    Publication Date: 2013-08-29
    Description: The Chandra X-Ray Observatory is the X-ray component of NASA's Great observatories which also includes the recently decommissioned Compton Gamma Ray Observatory, the Hubble Space Telescope, and the soon to be launched Space Infra Red Telescope Facility. Chandra is a unique X-ray astronomy facility for high-resolution imaging and for high-resolution spectroscopy. Chandra's performance advantage over other X-ray observatories is analogous to that of the Hubble Space Telescope over ground-based observatories. Chandra is a NASA facility that provides scientific data to the international astronomical community in response to proposals for its use. Data becomes public one year after the observation. The Observatory is the product of the efforts of many commercial, academic, and government organizations in the United States and Europe. NASA's Marshall Space Flight Center (MSFC) manages the Project and provides Project Science; TRW Space and Electronics Group served as prime contractor responsible for providing the spacecraft, the telescope, and assembling and testing the observatory; the Smithsonian Astrophysical Observatory (SAO) provides technical support and is responsible for ground operations.
    Keywords: Astronomy
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  • 58
    Publication Date: 2013-08-29
    Description: The Next Generation Space Telescope (NGST) is a large aperture space telescope designated to succeed the Hubble Space Telescope (HST). NGST will continue the recent breakthroughs of HST in our understanding of the earliest origins of stars, galaxies and the elements that are the foundations of Life. It is expected that the costs of NGST should be kept within a fraction of those for HST. The ground segment has a goal of reducing the cost of NGST in comparison to HST by 50% to 75%. To mitigate risks for NGST a flight demonstrator called Nexus is planned for 2005. Nexus is a smaller scale telescope, which plans to test the deployment and optical stability of the telescope, the "Wave Front Control" process, and the thermal performance of the sunshield. The Nexus Ground System will be developed by GSFC and STSci, and the NGST Ground System will be developed by STSci. The authors of this paper are engaged in a study to evaluate and recommend selection of a Command and Telemetry system for each of these Ground Systems. This paper focuses on the process of selecting the real-time Command and Telemetry system for NGST. We would like to use the conference as a sounding board as we make a selection.
    Keywords: Astronomy
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  • 59
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    In:  CASI
    Publication Date: 2012-10-23
    Description: Theoretically self-consistent calculations for photoionization and (e + ion) recombination are described. The same eigenfunction expansion for the ion is employed in coupled channel calculations for both processes, thus ensuring consistency between cross sections and rates. The theoretical treatment of (e + ion) recombination subsumes both the non-resonant recombination ("radiative recombination"), and the resonant recombination ("di-electronic recombination") processes in a unified scheme. In addition to the total, unified recombination rates, level-specific recombination rates and photoionization cross sections are obtained for a large number of atomic levels. Both relativistic Breit-Pauli, and non-relativistic LS coupling, calculations are carried out in the close coupling approximation using the R-matrix method. Although the calculations are computationally intensive, they yield nearly all photoionization and recombination parameters needed for astrophysical photoionization models with higher precision than hitherto possible, estimated at about 10-20% from comparison with experimentally available data (including experimentally derived DR rates). Results are electronically available for over 40 atoms and ions. Photoionization and recombination of He-, and Li-like C and Fe are described for X-ray modeling. The unified method yields total and complete (e+ion) recombination rate coefficients, that can not otherwise be obtained theoretically or experimentally.
    Keywords: Astronomy
    Type: Atomic Data Needs for X-ray Astronomy; 77-84; NASA/CP-2000-209968
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  • 60
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    In:  CASI
    Publication Date: 2012-10-23
    Description: Recent advances in theoretical atomic physics have enabled large-scale calculation of atomic parameters for a variety of atomic processes with high degree of precision. The development and application of these methods is the aim of the Iron Project. At present the primary focus is on collisional processes for all ions of iron, Fe I - FeXXVI, and other iron-peak elements; new work on radiative processes has also been initiated. Varied applications of the Iron Project work to X-ray astronomy are discussed, and more general applications to other spectral ranges are pointed out. The IP work forms the basis for more specialized projects such as the RmaX Project, and the work on photoionization/recombination, and aims to provide a comprehensive and self-consistent set of accurate collisional and radiative cross sections, and transition probabilities, within the framework of relativistic close coupling formulation using the Breit-Pauli R-Matrix method. An illustrative example is presented of how the IP data may be utilized in the formation of X-ray spectra of the K alpha complex at 6.7 keV from He-like Fe XXV.
    Keywords: Astronomy
    Type: Atomic Data Needs for X-ray Astronomy; 69-75; NASA/CP-2000-209968
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  • 61
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    In:  CASI
    Publication Date: 2012-10-23
    Description: The new x-ray astronomical observatories have sufficient spectroscopic capability to allow the determination of plasma conditions in the form of velocities, temperatures, densities, and turbulence parameters at levels that were previously unattainable. The utilization of these diagnostics are possible only if the atomic and plasma physics are well-enough understood to match the observational sensitivity.
    Keywords: Astronomy
    Type: Atomic Data Needs for X-ray Astronomy; 1-4; NASA/CP-2000-209968
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  • 62
    facet.materialart.
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    In:  CASI
    Publication Date: 2012-10-23
    Description: Physical properties such as temperature and electron density of solar plasma and other astrophysical objects can be inferred from EUV and X-ray emission lines observed from space. These lines are emitted when the higher states of an ion are excited by electron impact and then decay by photon emission. Excitation cross sections are required for the spectroscopic analyses of the observations and various approximations have been used to calculate the scattering functions. One of them which has been widely used is a distorted wave approximation. This approximation, along with its applications to solar observations, is discussed. The Bowen fluorescence mechanism and optical depth effects are also discussed. It is concluded that such calculations are reliable for highly charged ions and for high electron temperatures.
    Keywords: Astronomy
    Type: Atomic Data Needs for X-ray Astronomy; 41-63; NASA/CP-2000-209968
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  • 63
    Publication Date: 2012-10-23
    Description: Several different approximations and techniques have been developed for the calculation of atomic structure, ionization, and excitation of atoms and ions. These techniques have been used to compute large amounts of spectroscopic data of various levels of accuracy. This paper presents a review of these theoretical methods to help non-experts in atomic physics to better understand the qualities and limitations of various data sources and assess how reliable are spectral models based on those data.
    Keywords: Astronomy
    Type: Atomic Data Needs for X-ray Astronomy; 25-40; NASA/CP-2000-209968
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  • 64
    Publication Date: 2013-08-31
    Description: The Next Generation Space Telescope (NGST), part of NASA's Origins program, is a follow on to the Hubble Space Telescope expected to provide timely new science along with answering fundamental questions. NGST is a large diameter, infrared optimized telescope with imaging and spectrographic detectors which will be used to help study the origin of galaxies. Due to the large data NGST will collect, Goddard Space Flight Center has considered the use of optical communications for data downlink. The Optical Communications Group at the Jet Propulsion Laboratory has performed a study on optical communications systems for NGST. The objective of the study was to evaluate the benefits gained through the use of optical communication technologies. Studies were performed for each of four proposed NGST orbits. The orbits considered were an elliptical orbit about the semi stable second Lagrangian point, a 1 by 3 AU elliptic orbit around the sun, a 1 AU drift orbit, and a 1 AU drift orbit at a 15 degree incline to the ecliptic plane. An appropriate optical communications system was determined for each orbit. Systems were evaluated in terms of mass, power consumption, size, and cost for each of the four proposed orbits.
    Keywords: Astronomy
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  • 65
    Publication Date: 2011-08-23
    Description: We report an observation by the Chandra X-Ray Observatory of 4U 2127+119, the X-ray source identified with the globular cluster M15. The Chandra observation reveals that 4U 2127+119 is in fact two bright sources, separated by 2.7 arcsec. One source is associated with AC 211, the previously identified optical counterpart to 4U 2127+119, a low-mass X-ray binary (LMXB). The second source, M15 X-2, is coincident with a 19th U magnitude blue star that is 3.3 arcsec from the cluster core. The Chandra count rate of M15 X-2 is 2.5 times higher than that of AC 211. Prior to the 0.5 arcsec imaging capability of Chandra, the presence of two so closely separated bright sources would not have been resolved. The optical counterpart, X-ray luminosity, and spectrum of M15 X-2 are consistent with it also being an LMXB system. This is the first time that two LMXBs have been seen to be simultaneously active in a globular cluster. The discovery of a second active LMXB in M15 solves a long-standing puzzle where the properties of AC 211 appear consistent with it being dominated by an extended accretion disk corona, and yet 4U 2127+119 also shows luminous X-ray bursts requiring that the neutron star be directly visible. The resolution of 4U 2127+119 into two sources suggests that the X-ray bursts did not come from AC 211 but rather from M15 X-2. We discuss the implications of this discovery for understanding the origin and evolution of LMXBs in globular clusters as well as X-ray observations of globular clusters in nearby galaxies.
    Keywords: Astronomy
    Type: The Astrophysical Journal; Volume 561
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  • 66
    Publication Date: 2016-06-07
    Description: This paper presents a brief overview of thermal analysis, evaluating the University of Arizona mirror design, for the Next Generation Space Telescope (NGST) Pre-Phase A vehicle concept. Model building begins using Thermal Desktop(TM), by Cullimore and Ring Technologies, to import a NASTRAN bulk data file from the structural model of the mirror assembly. Using AutoCAD(R) capabilities, additional surfaces are added to simulate the thermal aspects of the problem which, for due reason, are not part of the structural model. Surfaces are then available to accept thermophysical and thermo-optical properties. Thermal Desktop(TM) calculates radiation conductors using Monte Carlo simulations. Then Thermal Desktop(TM) generates the SINDA input file having a one-to-one correspondence with the NASTRAN node and element definitions. A model is now available to evaluate the mirror design in the radiation dominated environment, conduct parametric trade studies of the thermal design, and provide temperatures to the finite element structural model.
    Keywords: Astronomy
    Type: The Tenth Thermal and Fluids Analysis Workshop; NASA/CP-2001-211141
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  • 67
    Publication Date: 2018-06-08
    Description: Talks about how scientists can reach out to the community by public talks.
    Keywords: Astronomy
    Type: Division for Planetary Sciences Meeting of the American Astronomical Society; New Orleans, LA; United States
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  • 68
    Publication Date: 2018-06-08
    Description: This paper discusses the B and V photometry being obtained for variable stars in the northeast arm of the Small Magellanic Cloud (SMC).
    Keywords: Astronomy
    Type: Astronomical Journal
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  • 69
    Publication Date: 2018-06-08
    Description: We examine the early angular momentum history of stars in young clusters.
    Keywords: Astronomy
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  • 70
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    Publication Date: 2018-06-08
    Keywords: Astronomy
    Type: American Astronomical Society #198; Pasadena, CA; United States
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  • 71
    Publication Date: 2018-06-08
    Keywords: Astronomy
    Type: AAS 198th Meeting; Pasadena, CA; United States
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  • 72
    Publication Date: 2018-06-08
    Keywords: Astronomy
    Type: Bulletin of the American Astronomical Society
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  • 73
    Publication Date: 2018-06-08
    Keywords: Astronomy
    Type: Bulletin of the American Astronomical Society
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  • 74
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    Publication Date: 2018-06-08
    Keywords: Astronomy
    Type: Bulletin of the American Astronomical Society
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  • 75
    Publication Date: 2018-06-11
    Description: Numerical simulations of the orbital evolution of dust particles from Edgeworth-Kuiper Belt (EKB) objects show that the three giant planets, Neptune, Jupiter, and Saturn impose distinct and dramatic signatures on the overall distribution of EKB dust particles. The features are very similar to those observed in the dust disk around the nearby star Eridani. Numerical simulations of dust particles in the epsilon Eridani system show that planetary perturbations may be responsible for the observed features
    Keywords: Astronomy
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  • 76
    Publication Date: 2018-06-08
    Description: Comparisons of measurements from interferometry, spectroscopy, precision photometry, lunar occultation, and Hipparcos not only checks the accuracy of the distance to the Hyades, but also provides an accurate empirical mass-luminosity relation, and a good estimate of the age of the Hyades.
    Keywords: Astronomy
    Type: The 195th Meeting of the American Astronomical Society; Atlanta, GA; United States
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  • 77
    Publication Date: 2018-06-08
    Keywords: Astronomy
    Type: 195th Meeting of the American Astronomical Society; Atlanta, GA; United States
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  • 78
    Publication Date: 2018-06-08
    Keywords: Astronomy
    Type: 195th Meeting of the American Astronomical Society; Atlanta, GA; United States
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  • 79
    Publication Date: 2018-06-08
    Keywords: Astronomy
    Type: American Astronomical Society Meeting; Atlanta, GA; United States
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  • 80
    Publication Date: 2018-06-08
    Keywords: Astronomy
    Type: 195th American Astronomical Society; United States
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  • 81
    Publication Date: 2018-06-08
    Keywords: Astronomy
    Type: Astronomical Telescopes and Instrumentation AS04-Interferometry in Optical Astronomy; Munich; Germany
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  • 82
    Publication Date: 2018-06-08
    Keywords: Astronomy
    Type: Division for Planetary Sciences Meeting of the American Astronomical Society; Pasadena, CA; United States
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  • 83
    Publication Date: 2018-06-08
    Description: We present near-infrared images of the supernova remnant RCW 103 from the Two Micron All Sky Survey (2MASS).
    Keywords: Astronomy
    Type: Young Supernova Remnants; College Park, MD; United States
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  • 84
    Publication Date: 2018-06-08
    Keywords: Astronomy
    Type: International Astronomical Union (IAU) Symposium Zoo The Formation of Binary Stars; Potsdam; Germany
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  • 85
    Publication Date: 2018-06-06
    Description: A study was made of two ultraluminous X-ray soures (ULXs) in the nearby face-on, late-type Sb galaxy NGC 1313 using data from Suzaku, the 5th Japanese X-ray satellite. Within the 90 ks observation, both sources named X-1 and X-2 exhibited luminosity change by about 50%. The 0.4-10 keV X-ray luminosity was measured to be 2.5 x 10(exp 40) erg per second and 5.8 x 10 erg per second for X-1 and X-2, respectively, requiring a black hole of 50-200 solar mass in order not to exceed the Eddingtion limit. For X-1: the spectrum exhibited a strong power-law component with a high energy cutoff which is thought to arise from strong Comptonization by a disk corona, suggesting the source was in a very high state. Absorption line features with equivalent widths of 40-80 eV found at 7.0 keV and 7.8 keV in the X-1 spectrum support the presence of a highly ionized plasma and a high mass accretion rate on the system. Oxygen abundance of the NGC 1313 circumstellar matter toward X-1 was found to be subsolar, viz. O/H = (5.0 plus or minus 1.0) x 10(exp -4). The spectrum of X-2 in fainter phase is best represented by a multicolor disk blackbody model with T (sub in) = 1.2-1.3 keV and becomes flatter as the flux increases; the source is interpreted to be in a slim disk state.
    Keywords: Astronomy
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  • 86
    Publication Date: 2018-06-08
    Keywords: Astronomy
    Type: American Astronomical Society 197th Meeting; San Diego, CA; United States
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  • 87
    Publication Date: 2018-06-08
    Keywords: Astronomy
    Type: 197th Meeting of the American Astronomical Society; San Diego, CA; United States
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  • 88
    Publication Date: 2018-06-08
    Description: We present the results of a simple, highly efficient 2MASS color-based survey that has already discovered 140 previously unknown red AGN and QSOs. These objects are near-infrared-bright and relatively nearby; the media redshift of the sample is z=0.25, and all but two have z〈0.7.
    Keywords: Astronomy
    Type: 197th Meeting of the American Astronomical Society; San Diego, CA; United States
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  • 89
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    Publication Date: 2018-06-08
    Keywords: Astronomy
    Type: 197th Meeting of the American Astronomical Society; San Diego, CA; United States
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  • 90
    Publication Date: 2018-06-08
    Keywords: Astronomy
    Type: 197th Meeting of the American Astronomical Society; San Diego, CA; United States
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  • 91
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    Publication Date: 2018-06-08
    Keywords: Astronomy
    Type: Astronomical Data Analysis Software & Systems X; Boston, MA; United States
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  • 92
    Publication Date: 2018-06-08
    Keywords: Astronomy
    Type: 197th Meeting of the American Astronomical Society; San Diego, CA; United States
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  • 93
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    Publication Date: 2018-06-08
    Keywords: Astronomy
    Type: Division for Planetary Sciences Meeting of the American Astronomical Society; Pasadena, CA; United States
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  • 94
    Publication Date: 2018-06-08
    Keywords: Astronomy
    Type: Division for Planetary Sciences Meeting of the American Astronomical Society; Pasadena, CA; United States
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  • 95
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    Publication Date: 2018-06-08
    Keywords: Astronomy
    Type: 197th Meeting of the American Astronomical Society; San Diego, CA; United States
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  • 96
    Publication Date: 2018-06-08
    Keywords: Astronomy
    Type: 197th Meeting of the American Astronomical Society; San Diego, CA; United States
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  • 97
    Publication Date: 2018-06-08
    Description: We discuss the development of the Differential Phase detection technique for the Keck Interferometer Hot Jupiter Key Science Program.
    Keywords: Astronomy
    Type: International Astronomical Union (IAU) Symposium 202 : Planetary Systems in the Universe: Observation, Formation and Evolution; Manchester; United Kingdom
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  • 98
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    Publication Date: 2018-06-08
    Keywords: Astronomy
    Type: Division for Planetary Sciences Meeting of the American Astronomical Society; Pasadena, CA; United States
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  • 99
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    Publication Date: 2018-06-08
    Description: Extensive observations of comet Hale-Bopp from the ground and space have considerably expanded our knowledge of cometary dust.
    Keywords: Astronomy
    Type: International Astronomical Union (IAU) Colloquium 181; Canterbury; United Kingdom|Proceedings of International Astronomical Union (IAU) Colloquium 181
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  • 100
    Publication Date: 2018-06-08
    Keywords: Astronomy
    Type: Division for Planetary Sciences Meeting of the American Astronomical Society; Pasadena, CA; United States
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