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  • Other Sources  (19)
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  • 1
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    The case for the relativistic hot big bang cosmology (1991)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: What has become the standard model in cosmology is described, and some highlights are presented of the now substantial range of evidence that most cosmologists believe convincingly establishes this model, the relativistic hot big bang cosmology. It is shown that this model has yielded a set of interpretations and successful predictions that substantially outnumber the elements used in devising the theory, with no well-established empirical contradictions. Brief speculations are made on how the open puzzles and work in progress might affect future developments in this field.
    Keywords: ASTROPHYSICS
    Type: Nature (ISSN 0028-0836); 352; 769-776
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  • 2
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    Unusual radio source MG1131+0456 - A possible Einstein ring (1988)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: The discovery of extremely unusual structure in the radio source MG1131+0456 is reported. In a radio map with subsarcsecond resolution the object appears as an elliptical ring of emission accompanied by a pair of more compact sources, nearly diametrically opposed and offset by about 0.3 arcsec to the southwest of the ring. There is a faint, slightly extended, optical counterpart. A continuum but no emission lines is detected in its spectrum; therefore, the redshift of the counterpart is unknown. The radio morphology suggests that this source may be an example of an 'Einstein ring', a highly symmetric case of gravitational lensing in which the source is imaged into a ring. Other explanations are considered and excluded by the data. Another possibility is that MG1131+04565 represents a new type of astronomical object.
    Keywords: ASTROPHYSICS
    Type: Nature (ISSN 0028-0836); 333; 537-540
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  • 3
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    The statistics of gravitational lenses - The distributions of image angular separations and lens redshifts (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: An analytical calculation is presented which determines the probability that the light from a distant quasar can be lensed by objects in a different redshift range. Three types of information are used to make the calculation: (1) the physical properties of the intervening scattering lenses; (2) the intrinsic properties of the quasars and (3) the selection procedures by which the quasar samples are acquired. A series of differential equations is given in which the probability is derived, and a number of recommendations are offered with respect to VLA and Space Telescope observations of quasars lensed in this way.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 284; 1-22
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  • 4
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    Study of the fluctuations in the cosmic X-ray background (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The emerging picture indicates that neither the total cosmic X-ray background (CXB) flux nor the fluctuations are completely dominated by any single class of sources. Quasars clearly contribute a substantial fraction of the total flux while galaxy cluster X-ray sources and galactic nuclear activity also make nonnegligible contributions. It appears that from the large angular scale CXB galaxy correlations that no class of relatively low liminosity X-ray sources associated with galaxies can play a major role in supplying the total flux. The origin of the fluctuations looks more complex. It is hard to avoid the conclusion that the NGP-SGP difference and some other features of the CXB map are associated with the local anisotropy in the galactic distribution (the local supercluster). It also appears reasonable to some suppose that at least some large angular structures in the CXB are due to emission from hot galactic halo gs.
    Keywords: SPACE RADIATION
    Type: NASA-CR-164840
    Format: application/pdf
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  • 5
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    Orbital Characterization of GJ1108A System, and Comparison of Dynamical Mass with Model-Derived Mass for Resolved Binaries (2018)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: We report an orbital characterization of GJ1108Aab that is a low-mass binary system in the pre-main-sequence phase. Via the combination of astrometry using adaptive optics and radial velocity measurements, an eccentric orbital solution of e = 0.63 is obtained, which might be induced by the KozaiLidov mechanism with a widely separated GJ1108B system. Combined with several observed properties, we conrm that the system is indeed young. Columba is the most probable moving group, to which the GJ1108A system belongs, although its membership to the group has not been established. If the age of Columba is assumed for GJ1108A, the dynamical masses of both GJ1108Aa and GJ1108Ab (M(sub dynamical,GJ1108Aa) = 0.72 0.04 Solar Mass and M(sub dynamical,GJ1108Ab) = 0.30 0.03 Solar Mass) are more massive than what an evolutionary model predicts based on the age and luminosities. We consider that the discrepancy in mass comparison can be attributed to an age uncertainty; the system is likely older than stars in Columba, and effects that are not implemented in classical models such as accretion history and magnetic activity are not preferred to explain the mass discrepancy. We also discuss the performance of the evolutionary model by compiling similar low-mass objects in the evolutionary state based on the literature. Consequently, it is suggested that the current model on average reproduces the mass of resolved low-mass binaries without any signicant offsets.
    Keywords: Astrophysics
    Type: GSFC-E-DAA-TN64800 , The Astrophysical Journal (ISSN 0004-637X) (e-ISSN 1538-4357); 865; 2; 152
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  • 6
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    The correlation of the cosmic X-ray background with the light of galaxies (1980)
    In:  Other Sources
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    Publication Date: 2019-06-27
    Description: Models for the origin of the cosmic X-ray background (CXB) radiation attribute it to numerous weak, unresolved discrete sources (e.g., active galactic nuclei), to some diffuse emission mechanism (e.g., thermal bremmstrahlung from a hot intergalactic plasma), or to an unresolved population of discrete sources which evolve substantially with redshift (e.g., quasars). It is shown that the comparison of the CXB flux variations with flux variations in the light from galaxies can measure the relative contribution of these possible sources of the CXB. Applying the technique to available Uhuru data, it is found that the absence of correlation between the optical flux variations and the X-ray flux variations sets an upper limit of approximately 50% on the fraction of the CXB originating with any classes of X-ray sources substantially represented among bright (apparent photographic magnitude less than or equal to 15.5) galaxies. The data are consistent with nearly all of the CXB being due to diffuse emission or to a class of sources whose density increases rapidly with redshift.
    Keywords: SPACE RADIATION
    Type: Astrophysical Journal; vol. 236
    Format: text
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  • 7
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    Filamentary galaxy clustering - A mapping algorithm (1983)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: A simple and objective algorithm is presented which not only accurately identifies the filamentary structures in the Shane-Wirtanen galaxy count catalog, but also finds a set of visually less impressive filaments in a static hierarchical model of the clustering conducted by Soneira and Peebles (1978). The statistical properties of the elements in the model, while very similar to those in the data, show a significant excess of long and bright filaments in the data relative to the model. Two possible interpretations of these results are presented and discussed.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 273; 16-23
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  • 8
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    Polarimetric Imaging of Large Cavity Structures in the Pre-transitional Protoplanetary Disk around PDS 70: Observations of the Disk (2012)
    In:  CASI
    Details
    Publication Date: 2019-07-12
    Description: We present high resolution H-band polarized intensity (PI; FWHM = 0."1: 14 AU) and L'-band imaging data (FWHM = 0."11: 15 AU) of the circumstellar disk around the weak-lined T Tauri star PDS 70 in Centaurus at a radial distance of 28 AU (0."2) up to 210 AU (1."5). In both images, a giant inner gap is clearly resolvro for the first time, and the radius of the gap is approx 70 AU. Our data show that the geometric center of the disk shifts by approx 6 AU toward the minor axis. We confirm that the brown dwarf companion candidate to the north of PDS 70 is a background star based on its proper motion. As a result of SED fitting by Monte Carlo radiative transfer modeling, we infer the existence of an optically thick inner disk at a few AU. Combining our observations and modeling, we classify the disk of PDS 70 as a pre-transitional disk. Furthermore, based on the analysis of L'-band imaging data, we put an upper limit mass of companions at approx 30 to approx 50M(sub J) within the gap. Taking account of the presence of the large and sharp gap, we suggest that the gap could be formed by dynamical interactions of sub-stellar companions or multiple unseen giant planets in the gap.
    Keywords: Astronomy
    Type: GSFC.JA.7392.2012
    Format: application/pdf
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  • 9
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    A gravitational lens candidate with an unusually red optical counterpart (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: The properties of the strong radio source MG0414 + 0534 are described. It is found to display many of the properties expected in a gravitational lens system. At radio wavelengths and 0.5-arcsec resolution, MG0414 + 0534 is made up of four compact components whose unusual configuration and relative flux densities are similar to those found in confirmed four-image gravitational lens systems. At optical wavelengths three objects are detected, consistent with there being optical objects at the positions of the radio components, given the lower optical resolution. The radio and optical centroid positions agree within the astrometric errors, and the relative ordering of the fluxes is the same. The colors and radiooptical spectral indices are similar, but there are differences larger than the photometric errors and the measured variability (about 30 percent). Extinction by dust might simultaneously explain the unusually red color and the absence of light from a lens.
    Keywords: ASTROPHYSICS
    Type: Astronomical Journal (ISSN 0004-6256); 104; 3 Se; 968-979
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  • 10
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    A search for gravitational lenses - Search strategies and a preliminary upper limit on the density of lenses (1987)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Keywords: ASTROPHYSICS
    Type: Texas Symposium on Relativistic Astrophysics; Dec 14, 1986 - Dec 19, 1986; Chicago, IL; United States
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