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  • 1
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    Optical diameters of stars measured with the Mt. Wilson Mark III interferometer (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Reliable stellar angular diameters can now be determined using the Mark III Optical Interferometer located on Mt. Wilson, California. The Mark III is a Michelson Interferometer capable of measuring the interferometric fringe visibility for stars using interferometer baselines varying from 3 to 31.5 meters in length. Angular diameters measured with the Mark III Optical Interferometer are presented for 12 stars at wavelengths of 450 and 800 nm.
    Keywords: ASTRONOMY
    Type: Amplitude and intensity spatial interferometry; Feb 14, 1990 - Feb 16, 1990; Tucson, AZ; United States
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  • 2
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    Radar images of asteroid 1627 Ivar (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Radar echoes from the near-earth asteroid 1627 Ivar, whose orbit crosses the earth's, reveal it to be about twice as long as it is wide, with a maximum dimension no less than 7 km and probably within 20 percent of 12 km. The surface is fairly smooth at centimeter-to-meter scales but appears irregular and nonconvex at kilometer scales.
    Keywords: ASTRONOMY
    Type: Astronomical Journal (ISSN 0004-6256); 99; 2012-201
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  • 3
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    Ephemerides of the major Neptunian satellites determined from earth-based astrometric and Voyager imaging observations (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The Voyager project used Neptunian satellite ephemerides to support both navigation and acquisition of scientific data. The development of postencounter ephemerides for the satellites Triton, Nereid, and 1989N1 is discussed. Primary results are the final set of model parameters which generate orbits that best fit both the earth-based satellite observations and data acquired by Voyager. The ephemerides are compared with those generated preencounter, and the accuracy of the final ephemerides is assessed. Mean orbital elements are also provided as a geometrical representation for the satellite orbits.
    Keywords: ASTRONOMY
    Type: AIAA PAPER 90-2881 , AIAA/AAS Astrodynamics Conference; Aug 20, 1990 - Aug 22, 1990; Portland, OR; United States
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  • 4
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    New observations and a photographic atlas of polar-ring galaxies (1990)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: A photographic atlas of polar-ring galaxies and related objects is presented. The atlas includes kinematically confirmed polar-ring galaxies (category A), good candidates based on their morphological appearance (category B), possible candidates (category C), and possibly related objects (category D). New photometric and kinematic observations are reported for several galaxies in the catalog, including observations that show that UGC 7576 and UGC 9796 ( = II ZW 73) are S0 galaxies with polar rings. Roughly 0.5 percent of all nearby S0 galaxies appear to have polar rings. When corrected for various selection effects (e.g., nonoptimal viewing orientation, possible dimming, or limited lifetime of the ring) the percentage increases to about 5 percent of S0 galaxies which have, or have had a polar ring.
    Keywords: ASTRONOMY
    Type: Astronomical Journal (ISSN 0004-6256); 100; 1489-152
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  • 5
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    A radio optical reference frame. I - Precise radio source positions determined by Mark III VLBI - Observations from 1979 to 1988 and a tie to the FK5 (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Observations from 600 Mark III VLBI experiments from 1979 to 1988, resulting in 237,681 acceptable pairs of group delay and phase delay rate observations, have been used to derive positions of 182 extragalactic radio sources with typical formal standard errors less than 1 mas. The sources are distributed fairly evenly above delta = -30 deg, and 70 sources have delta greater than 0 deg. Analysis with different troposphere models, as well as internal and external comparisons, indicates that a coordinate frame defined by this set of radio sources should be reliable at the 1 mas level. The right ascension zero point of this reference frame has been aligned with the FK5 by using the optical positions of 28 extragalactic radio sources whose positions are on the FK5 system. Because of known defects in the knowledge of astronomical constants, daily nutation offsets in longitude and obliquity were determined relative to an arbitrary reference day in the set of experiments.
    Keywords: ASTRONOMY
    Type: Astronomical Journal (ISSN 0004-6256); 99; 1284-129
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  • 6
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    High resolution solar spectrometer system for measuring atmospheric constituents (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A mid-IR Michelson interferometer capable of obtaining 0.002/cm resolution solar spectra has been developed for balloon use. The interferometer is based on the Bomem self-aligning instrument, and is equipped with a solar tracking system, telemetry, and recording systems, as well as temperature control and gondola orientation. The interferometer has made two successful flights in the 7-14-micron interval up to 40 km. The basic systems are described and sample spectra are presented.
    Keywords: ASTRONOMY
    Type: Applied Optics (ISSN 0003-6935); 29; 1520-152
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  • 7
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    Development of components for submillimeter wave heterodyne radiometers at JPL (1990)
    In:  CASI
    Details
    Publication Date: 2013-08-29
    Description: Components for the key elements of submillimeter wave heterodyne receivers are described. The devices and components are inherently space qualifiable having low power and mass needs and exhibiting robustness. Nb and NbN superconductor insulator superconductor (SIS) tunnel junctions are selected for the nonlinear mixing element because of their robustness. NbN exhibits a large superconducting bandgap, allowing operation in excess of 1500 GHz. Both waveguide mounts, for the lower frequencies and planar antenna mixer mounts for the higher frequency range, are used. Quasi-optical components are used for frequency multiplexing and combining.
    Keywords: ASTRONOMY
    Type: ESA, From Ground-Based to Space-Borne Sub-mm Astronomy; p 211-214
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  • 8
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    Linear regression in astronomy. I (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Five methods for obtaining linear regression fits to bivariate data with unknown or insignificant measurement errors are discussed: ordinary least-squares (OLS) regression of Y on X, OLS regression of X on Y, the bisector of the two OLS lines, orthogonal regression, and 'reduced major-axis' regression. These methods have been used by various researchers in observational astronomy, most importantly in cosmic distance scale applications. Formulas for calculating the slope and intercept coefficients and their uncertainties are given for all the methods, including a new general form of the OLS variance estimates. The accuracy of the formulas was confirmed using numerical simulations. The applicability of the procedures is discussed with respect to their mathematical properties, the nature of the astronomical data under consideration, and the scientific purpose of the regression. It is found that, for problems needing symmetrical treatment of the variables, the OLS bisector performs significantly better than orthogonal or reduced major-axis regression.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 364; 104-113
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  • 9
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    A 1.49 GHz atlas of the IRAS Bright Galaxy Sample (1990)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: The VLA has been used in its A-, B-, C-, and D-configurations to make 1.49 GHz maps of sources in both the original and revised IRAS Bright Galaxy Samples of strong extragalactic sources selected at a wavelength of 60 microns. Integrated 1.49 GHz flux densities were obtained from the lowest resolution maps, and maps were made with higher resolution so that nearly all of the radio sources have been at least partially resolved. Only NGC 1377 was not detected at 1.49 GHz. An atlas of contour maps, a table of total flux densities plus other radio source parameters, and references to published radio maps are given. Since the infrared and radio continuum brightness distributions of IR-selected galaxies are usually similar, these high-resolution radio maps can be used as substitutes for the unavailable IR maps to indicate the sizes and precise locations of the IR-emitting regions.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal Supplement Series (ISSN 0067-0049); 73; 359-400
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  • 10
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    15 GHz space VLBI observations using an antenna on a TDRSS satellite (1990)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: A 4.9 m diameter antenna in earth orbit, part of the Tracking and Data Relay Satellite System, was previously used for space VLBI observations at 2.3 GHz. It has now been used successfully with two ground antennas for VLBI measurements at 15 GHz. Although the sensitivity (gain/system temperature) of the orbiting antenna was a factor of 6 poorer at 15 GHz than at 2.3 GHz, 11 out of 22 extragalactic sources were detected on space-ground baselines, up to a maximum baseline of 1.63 earth diameters. The results suggest that the distribution of source visibilities at 15 and 2.3 GHz are similar for these baseline lengths. Model-dependent brightness temperatures of 1-2.5 x 10 to the 12th K were derived for six sources. This suggests that sources with brightness temperatures in this range are as common at 15 GHz as at 2.3 GHz. The coherence on space-ground baselines (this includes effects due to the phase transfer from the ground to the satellite and the reconstruction of the spacecraft orbit) was 0.76 for 340 s integrations.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 358; 350-358
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