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  • ASTRONOMY  (522)
  • 2020-2024
  • 1990-1994  (308)
  • 1985-1989  (214)
  • 1955-1959
  • 1
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    A 380 GHz SIS receiver using Nb/AlO(x)/Nb junctions for a radioastronomical balloon-borne experiment: PRONAOS (1992)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The superheterodyne detection technique used for the spectrometer instrument of the PRONAOS project will provide a very high spectral resolution (delta nu/nu = 10(exp -6)). The most critical components are those located at the front-end of the receiver: their contribution dominates the total noise of the receiver. Therefore, it is important to perform accurate studies for specific components, such as mixers and multipliers working in the submillimeter wave range. Difficulties in generating enough local oscillator (LO) power at high frequencies make SIS mixers very desirable for operation above 300 GHz. The low LO power requirements and the low noise temperature of these mixers are the primary reason for building an SIS receiver. This paper reports the successful fabrication of small (less than or equal to 1 sq micron) Nb/Al-O(x)/Nb junctions and arrays with excellent I-V characteristics and very good reliability, resulting in a low noise receiver performance measured in the 368/380 GHz frequency range.
    Keywords: ASTRONOMY
    Type: Michigan Univ., The Third International Symposium on Space Terahertz Technology: Symposium Proceedings; p 189-209
    Format: application/pdf
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  • 2
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    Searches for millisecond pulsations in low-mass X-ray binaries, 2 (1994)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Coherent millisecond X-ray pulsations are expected from low-mass X-ray binaries (LMXBs), but remain undetected. Using the single-parameter Quadratic Coherence Recovery Technique (QCRT) to correct for unknown binary orbit motion, we have performed Fourier transform searches for coherent oscillations in all long, continuous segments of data obtained at 1 ms time resolution during Ginga observations of LMXB. We have searched the six known Z sources (GX 5-1, Cyg X-2, Sco X-1, GX 17+2, GX 340+0, and GX 349+2), seven of the 14 known atoll sources (GX 3+1. GX 9+1, GX 9+9, 1728-33. 1820-30, 1636-53 and 1608-52), the 'peculiar' source Cir X-1, and the high-mass binary Cyg X-3. We find no evidence for coherent pulsations in any of these sources, with 99% confidence limits on the pulsed fraction between 0.3% and 5.0% at frequencies below the Nyquist frequency of 512 Hz. A key assumption made in determining upper limits in previous searches is shown to be incorrect. We provide a recipe for correctly setting upper limits and detection thresholds. Finally we discuss and apply two strategies to improve sensitivity by utilizing multiple, independent, continuous segments of data with comparable count rates.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 435; 1; p. 362-371
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  • 3
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    A morphological filter for removing 'Cirrus-like' emission from far-infrared extragalactic IRAS fields (1993)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The presence of diffuse extended IR emission from the Galaxy in the form of the so called 'Galactic Cirrus' emission has hampered the exploration of the extragalactic sky at long IR wavelengths. We describe the development of a filter based on mathematical morphology which appears to be a promising approach to the problem of cirrus removal. The method of Greyscale Morphology was applied to a 100 micron IRAS image of the M81 group of galaxies. This is an extragalactic field which suffers from serious contamination from foreground Galactic 'cirrus'. Using a technique called 'sieving', it was found that the cirrus emission has a characteristic behavior which can be quantified in terms of an average spatial structure spectrum or growth function. This function was then used to attempt to remove 'cirrus' from the entire image. The result was a significant reduction of cirrus emission by an intensity factor of 15 compared with the original input image. The method appears to preserve extended emission in the spatially extended IR disks of M81 and M82 as well as distinguishing fainter galaxies within bright regions of galactic cirrus. The techniques may also be applicable to IR databases obtained with the Cosmic Background Explorer.
    Keywords: ASTRONOMY
    Type: Astronomical Journal (ISSN 0004-6256); 106; 4; p. 1664-1678.
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  • 4
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    Measurements of anisotropy in the cosmic microwave background radiation at 0.5 deg angular scales near the star gamma ursae minoris (1994)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: We present results from a four-frequency observation of a 6 deg x 0.6 deg strip of the sky centered near the star Gamma Ursae Minoris (GUM) during the fourth flight of the Millimeter-wave Anistropy experiment(MAX). The observation was made with a 1.4 deg peak-to-peak sinusoidal chop in all bands. The FWHM beam sizes were 0.55 deg +/- 0.05 deg at 3.5 per cm and 0.75 deg +/- 0.05 deg at 6, 9, and 14 per cm. During this observation significant correlated structure was observed at 3.5, 6 and 9 per cm with amplitudes similar to those observed in the GUM region during the second and third fligts of MAX. The frequency spectrum is consistent with cosmic microwave background (CMB) and inconsistent with thermal emission from interstellar dust. The extrapolated amplitudes of synchrotron and free-free emission are too small to account for the amplitude of the observed structure, If all of the structure is attributed to CMB anisotropy with a Gaussian autocorrelation function and a coherence angle of 25 min, then the most probable values of delta T/T(sub CMB) in the 3.5, 6 and 9 per cm bads are (4.3 +2.7/-1.6) x 10(exp -5), 2.8 (+4.3/-1/1) x 10(exp -5), and 3.5 (+3.0/-1.6) x 10(exp -5) (95% confidence upper and lower limits), respectively.
    Keywords: ASTRONOMY
    Type: The Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 430; 1; p. L1-L4
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  • 5
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    A degree scale anisotropy measurement of the cosmic microwave background near the star Gamma Ursae Minoris (1993)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: Results from a search for anisotropy in the cosmic microwave background (CMB) are presented from the third flight of the Millimeter-wave Anisotropy experiment. The CMB observation occurred over 1.37 hours and covered a 6.24 sq deg area of the sky where very little foreground emission is expected. Significant correlated structure is observed at 6 and 9/cm. At 12/cm we place an upper limit on the structure. The relative amplitudes at 6, 9, and 12/cm are consistent with a CMB spectrum. The spectrum of the structure is inconsistent with thermal emission from known forms of interstellar dust. Synchrotron and free-free emission would both require unusually flat spectral indices at cm wavelengths in order to account for the amplitude of the observed structure. Although known systematic errors are not expected to contribute significantly to any of the three optical channels, excess sidelobe contamination cannot be definitively ruled out. If all the structure is attributed to CMB anisotropy, a value of the weighted rms of the 6 and 9/cm channels of Delta T/T(CMB) = 4.7 +/- 0.8 x 10 exp -5 (+/- 1 sigma) was measured. If the CMB anisotropy is assumed to have a Gaussian autocorrelation function with a coherence angle of 25 arcmin, then the most probable value is Delta T/T(CMB) = 4.2 +1.7 or -1.1 x 10 exp -5, where the +/- refers to the 95 percent confidence limits.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 413; 1; p. L1-L5.
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  • 6
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    Measurements of anisotropy in the cosmic microwave background radiation at degree angular scales near the stars Sigma Herculis and Iota Draconis (1994)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: We present results from two four-frequency observations centered near the stars Sigma Herculis and Iota Draconis during the fourth flight of the Millimeter-wave Anisotropy eXperiment (MAX). The observations were made of 6 deg x 0.6 deg strips of the sky with a 1.4 deg peak to peak sinusoidal chop in all bands. The full width at half maximum (FWHM) beam sizes were calculated 0.55 deg +/- 0.05 deg at 3.5/cm and a 0.75 deg +/- 0.05 deg at 6, 9, and 14/cm. Significant correlated structures were observed at 3.5, 6, and 9/cm. The spectra of these signals are inconsistent with thermal emission from known interstellar dust populations. The extrapolated amplitudes of synchrotron and free-free emission are too small to account for the amplitude of the observed structures. If the observed structures are attributed to cosmic microwave background (CMB) anisotropy with a Gaussian autocorrelation function and a coherence angle of 25 min, then the most probable values at Delta T/T(sub CMB) = 3.1 (sup +1.7 sub -1.3) x 10(exp -5) for the Sigma Herculis scan, and Delta T/T(sub CMB) = 3.3(sup +1.1 sub -1.1) x 10(exp -5) for the Iota Draconis scan (95% confidence upper, lower limits).
    Keywords: ASTRONOMY
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 433; 2; p. L57-L60
    Format: text
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  • 7
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    Gravitational radiation observations on the moon (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The paper discusses the features of a laser-interferometer gravitational-wave observatory (LIGO) which is planned for operation in the Unitied States, with special attention given to the benefits gained from an addition of a low-mass laser gravitational wave antenna on the moon to the earth-based antennas. It is pointed out that the addition of a moon-based antenna would improve the angular resolution for burst signals by a factor of about 50 (in the plane containing the source, the moon, and the earth), which would be of major importance in studies of gravitational wave sources.
    Keywords: ASTRONOMY
    Type: Astrophysics from the Moon; Feb 05, 1990 - Feb 07, 1990; Annapolis, MD; United States
    Format: text
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  • 8
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    In-flight performance of the Faint Object Camera of the Hubble Space Telescope (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: An overview of the Faint Object Camera and its performance to date is presented. In particular, the detector's efficiency, the spatial uniformity of response, distortion characteristics, detector and sky background, detector linearity, spectrography, and operation are discussed. The effect of the severe spherical aberration of the telescope's primary mirror on the camera's point spread function is reviewed, as well as the impact it has on the camera's general performance. The scientific implications of the performance and the spherical aberration are outlined, with emphasis on possible remedies for spherical aberration, hardware remedies, and stellar population studies.
    Keywords: ASTRONOMY
    Type: Space Astronomical Telescopes and Instruments; Apr 01, 1991 - Apr 04, 1991; Orlando, FL; United States
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  • 9
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    Fabrication and characterization of replicated and lacquer-coated grazing incidence optics for X-ray astronomy (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: The fabrication and testing of electroformed replica Wolter I optics made from gold-coated lacquered mandrels are discussed. Also discussed is the testing of gold- and palladium-coated lacquered test flats. X-ray (5 keV for Wolter I mirror and 8-40 keV for test flats) and optical (NCP-1000 profiler) measurements were used to evaluate the mirrors.
    Keywords: ASTRONOMY
    Type: Optical Engineering (ISSN 0091-3286); 30; 1150-115
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  • 10
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    LMC stellar X-ray sources observed with ROSAT. 1: X-ray data and search for optical counterparts (1994)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Observations of Einstein Large Magellanic Cloud (LMC) X-ray point sources have been made with ROSAT's High-Resolution Imager to obtain accurate positions from which to search for optical counterparts. This paper is the first in a series reporting results of the ROSAT observations and subsequent optical observations. It includes the X-ray positions and fluxes, information about variability, optical finding charts for each source, a list of identified counterparts, and information about candidates which have been observed spectroscopically in each of the fields. Sixteen point sources were measured at a greater than 3 sigma level, while 15 other sources were either extended or less significant detections. About 50% of the sources are serendipitous detections (not found in previous surveys). More than half of the X-ray sources are variable. Sixteen of the sources have been optically identified or confirmed: six with foreground cool stars, four with Seyfert galaxies, two with signal-to-noise ratio (SNR) in the LMC, and four with peculiar hot LMC stars. Presumably the latter are all binaries, although only one (CAL 83) has been previously studied in detail.
    Keywords: ASTRONOMY
    Type: Astronomical Society of the Pacific, Publications (ISSN 0004-6280); 106; 702; p. 843-857
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