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  • 1
    Publication Date: 2011-08-16
    Description: Radar observations of a narrow belt of the surface of Mars, centered at 16 deg south latitude, show a very rugged terrain, with elevation differences greater than 13 kilometers from peak to valley. For nearby points, the relative altitude is measured to 40 meters at best; the precision is worse for points at different latitudes, or widely separated in longitude, because of orbital uncertainties. Some of the larger craters have been resolved, and their depth and, in some cases, the height of the raised rim have been measured. Where high resolution photographs are available, the correlation is excellent.
    Keywords: SPACE SCIENCES
    Type: Science; 174; Dec. 24
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  • 2
    Publication Date: 2011-08-11
    Description: Dissipation of magnetic fields at neutral lines in two-dimensional field with two intersecting shocks
    Keywords: SPACE SCIENCES
    Type: ASTROPHYSICAL JOURNAL
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  • 3
    Publication Date: 2016-06-07
    Description: Data from the International Ultraviolet Explorer satellite have revolutionized many concepts in extragalactic astronomy. These include the physical processes at work in the emitting gas characteristic of active objects, the nature of the continuum source itself in those objects, and the constituent hot stellar and gaseous components of normal galaxies. Several problems of extragalactic research investigated with IUE were reviewed.
    Keywords: ASTROPHYSICS
    Type: NASA. Goddard Space Flight Center The Universe at Ultraviolet Wavelengths: The First Two Yrs. of Intern. Ultraviolet Explorer; p 711-723
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  • 4
    Publication Date: 2019-06-28
    Description: Recent optical and spectrophotometric observations of all currently known DAO and DO hot white dwarf candidates from the Palomar-Green Survey are presented. The optical observations were carried out using the Kitt Peak National Observatory Intensified Image Dissector Scanner (IIDS) system, the Multiple Mirror Telescope (MMT), and two photon-counting Reticon systems. Ultraviolet spectrophotometry was obtained using the International Ultraviolet Explorer (IUE) short-wavelength and long-wavelength cameras. The following spectroscopic subgroups were identified in the observations: the cool DO stars with spectra showing H I features together with He II + H blends; the hot DO stars, with spectra exhibiting weak He II (+H) lines; and hydrogen-rich DAO stars with broad H lines and sharp H II lines at 4686 A. A fourth subgroup of stars resembling PG 1159 with He at He II lines at 4686, and a C, N ion blend in the optical spectrum were also found. The spectroscopic data were analyzed in terms of a grid of hot, high-gravity LTE model atmospheres composed of a mixture of hydrogen and helium, and atmospheric parameters are deduced for each class of objects. On the basis of the model atmosphere analysis, the local space density of the DO stars is estimated to be 1.9-3.0 x 10 to the -7th per cubic pc, depending on the scale height.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal Supplement Series (ISSN 0067-0049); 58; 379-411
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  • 5
    Publication Date: 2019-06-27
    Description: The paper deals with the spectra of six quasars, ranging in redshift from 0.23 to 2.04, obtained with the 45-cm telescope mounted on the IUE satellite. The average emission-line intensity ratio for L-alpha to H beta and the detection of higher-order Lyman emission lines in two objects are found to be inconsistent with a simple optically thick recombination model. The Lyman and Balmer line velocity profiles are identical. The emission lines in 3C 351 can be decomposed into sharp and broad components, with the sharp lines consistent with the recombination model.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 239
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  • 6
    Publication Date: 2019-06-28
    Description: Attention is given to the spectral energy distributions of nine high-redshift quasars between 1250 and 10,000 A. The distributions steepen shortward of about 1200 A in all but one object. The steepening's lack of correlation with QSO luminosity suggests that it arises from absorption by intervening material along the line of sight. Reddening may contribute to the steepening of the QSO continua, if dust lies along the line of sight to the continuum source, and is difficult to assess quantitatively. In QSOs with redshift sufficiently high for Lyman-alpha to be observed at high resolution, it is possible to account for the observed continuum steepening by the Lyman continuum absorption corresponding to the narrow Lyman-alpha absorption lines seen.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 281; 76-89
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  • 7
    Publication Date: 2019-06-28
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 263
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  • 8
    Publication Date: 2019-06-28
    Description: Two hot stars discovered in the Palomar Green survey which were found to exhibit peculiarly broad and strong Balmer lines possibly indicative of low magnetic fields are discussed. The stars, PG 1658+441 and PG 0136+251, were found to have extended trough-shaped Balmer and Lyman-alpha line profiles when compared to nonmagnetic dwarfs of similar temperatures. Further observations of PG 1658+441 show it to correspond to a 30,000 K pure hydrogen atmosphere and confirm its nature as a magnetic object with a longitudinal field strength of about 0.7 megagauss and a mean surface field of about 2.3 megagauss. PG 0136+251 is found to be a hotter star (40,000-50,000 K) with weaker lines. Although no strong evidence for magnetic line splitting was obtained, it is argued that neither a high surface gravity nor very rapid rotation can account for the Balmer line shapes. Results thus extend the range of magnetic degenerates to include very hot white dwarfs, and demonstrate the usefulness of line-widths as indicators of possible low-field magnetic sources.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 264
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  • 9
    Publication Date: 2019-06-28
    Description: The discovery of two magnetic white dwarfs culled from blue star surveys is reported. The surveys were carried out with the Mount Lemnon 1.5-meter reflecting telescope attached to a two-holer polarimeter/photometer. Spectral observations of the objects, (PG 1533 - 057, and K813 - 14), indicate the presence of hydrogen and Zeeman components. On the basis of dipolar field simulations, it is shown that PG 1533 - 057 has a polar field strength of 31 megagauss (MG) while K813 - 14 has a polar field strength of 29 MG. A third known white dwarf has a polar field strength of 18 MG. All the dwarfs had temperatures in the 11,000-20,000 K range. The possibility that a significant fraction of isolated magnetic degenerate stars could be the progeny of magnetic accreting binary systems is considered.
    Keywords: ASTROPHYSICS
    Type: Astronomical Society of the Pacific, Publications (ISSN 0004-6280); 97; 158-164
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  • 10
    Publication Date: 2019-06-27
    Description: Taking advantage of the favorable opposition of 1971, the Goldstone radar system, operating at 2388 MHz, was used to scan the Martian surface. Measurements of altitude and reflected power were taken approximately every 3 days. Each measurement represents an area 8 km E-W by 80 km N-S, the highest resolution attained to date. Altitude measurements obtained on different observing days were combined to produce altitude profiles for three complete rotations, each at different latitudes. Large-scale variations in altitudes cover a range of 14 km. Altitude changes of 5 in 30 km of longitude were observed. The altitude profiles show the heavy cratering of the surface, and several large craters (50-100 km) 1-2 km deep are easily seen.
    Keywords: SPACE SCIENCES
    Type: Icarus; 18; Jan. 197
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