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  • 1
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    An Occultation by Saturn's Rings on 1991 October 2-3 October 2-3 Observed with the Hubble Space Telescope (1993)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: An occultation of the star GSC 6323-01396 (V = 11.9) by Saturn's rings was observed with the High-Speed Photometer on the Hubble Space Telescope (HST) on 1991 October 2-3. This occultation occurred when Saturn was near a stationary point, so the apparent motion of Saturn relative to the star was dominated by the HST orbital motion (8 km/s). Data were recorded simultaneously at effective wavelengths of 3200 and 7500 A, with an integration time of 0.15 s. Fifteen segments of occultation data, totaling 6.8 h, were recorded in 13 successive orbits during the 20.0 h interval from UTC 1991 October 2, 19:35 until UTC 1991 October 3, 15:35. Occultations by 43 different features throughout the classical rings were unambiguously identified in the light curve, with a second occultation by 24 of them occurring due to spacecraft orbital parallax during this extremely slow event. Occultation times for features currently presumed circular were measured and employed in a geometrical model for the rings. This model, relating the observed occultation times to feature radii and longitudes, is presented here and is used in a least-squares fit for the pole direction and radius scale of Saturn's ring system.
    Keywords: ASTRONOMY
    Type: The Astronomical Journal (ISSN 0004-6256); 106; 6; p. 2544-2572
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  • 2
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    The Hubble Space Telescope high speed photometer (1988)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The Hubble Space Telescope will provide the opportunity to perform precise astronomical photometry above the disturbing effects of the atmosphere. The High Speed Photometer is designed to provide the observatory with a stable, precise photometer with wide dynamic range, broad wavelenth coverage, time resolution in the microsecond region, and polarimetric capability. Here, the scientific requirements for the instrument are examined, the unique design features of the photometer are explored, and the improvements to be expected over the performance of ground-based instruments are projected.
    Keywords: ASTRONOMY
    Type: NASA, Ames Research Center, Second Workshop on Improvements to Photometry; p 1-15
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  • 3
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    Optical polarization of Nova Monocerotis 1975 /= A0620-00/ (1976)
    In:  Other Sources
    Details
    Publication Date: 2011-08-17
    Description: The linear polarization of the optical counterpart of the transient X-ray source A0620-00 is interstellar in magnitude, position angle, and wavelength dependence. The magnitude of the polarization is consistent with a distance greater than 1 kpc.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal; 210; Dec. 15
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  • 4
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    Concurrent radio, infrared, optical and X-ray observations of the nucleus of the Seyfert galaxy NGC 4151 (1981)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The nucleus of the Seyfert galaxy NGC 4151 was observed during May and June 1977 at X-ray energies from 20 to 200 keV using the high-energy X-ray spectrometer on OSO 8 at radio frequencies of 2695 and 8085. Data were also taken in the visual, and at infrared wavelengths of 1 to 2 microns, and from 2 to 6 keV using the OSO 8 proportional counter. Optical data showed variability by a factor of 2 within the observing period, which is comparable to the variability in the 2 to 6 keV X-ray flux. No variability, however, was measured at infrared or radio frequencies. The composite spectrum from radio to gamma-ray is plotted, and it is found that the optical and X-ray fluxes varied during the observing period, although it is not known if they varied concurrently.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal; vol. 247
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  • 5
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    The high energy X-ray spectrum of 4U 1700-37 observed from OSO 8 (1980)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: The most intense hard X-ray source in the confused region in Scorpius has been identified as 4U 1700-37 (=HD 153919). Observations extending over three binary periods in 1978 September were carried out with the high-energy X-ray spectrometer on OSO 8. The 3.4 day modulation is seen above 20 keV with the intensity during eclipse being consistent with zero flux. The photonumber spectrum from 20 to 150 keV is well represented by a single power law with a photonumber spectral index of -2.77 + or - 0.35 or by a thermal bremsstrahlung spectrum with kT = 27 (+15, -7)keV. The counting rate above 20 keV outside of eclipse shows no evidence for the 96.8 minute X-ray modulation previously reported at lower energies. Despite the difficulties that exist in reconciling both the lack of periodic modulation in the emitted X-radiation and the orbital dynamics of the system with our currently accepted theories of the evolution and physical properties of neutron stars, the observed properties of 4U 1700-37 are all consistent with the source being a spherically accreting neutron star rather than a black hole.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal; vol. 238
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  • 6
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    High energy X-ray spectra of cygnus XR-1 observed from OSO-8 (1978)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: X-ray spectra of Cygnus XR-1 were measured with the scintillation spectrometer on board the OSO-8 satellite during a period of one and one-half to three weeks in each of the years from 1975 to 1977. Observations were made when the source was both in a high state and in a low state. Typical spectra of the source between 15 and 250 keV are presented. The observed pivoting effect is consistent with two temperature accretion disk models of the X-ray emitting region. No significant break in the spectrum occurred at energies up to 150 keV. The high state as defined in the 3 to 6 keV bandwidth was found to be the higher luminosity state of the X-ray source. One transition from a low to a high state occurred during observations. The time of occurrence of this and other transitions is consistent with the hypothesis that all intensity transitions occur near periastron of the binary system, and that such transitions are caused by changes in the mass transfer rate between the primary and the accretion disk around the secondary.
    Keywords: ASTRONOMY
    Type: NASA-TM-79626
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  • 7
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    X-ray observations of AM Herculis from OSO-8 (1979)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The white dwarf binary system AM Herculis (2A1815+500) was observed in X-rays at both low energies (E less 10 keV) and higher energies. The exact shape of the spectrum, particularly at the higher energies, has yet to be determined. Results from the high energy scintillation spectrometer on OSO-8 are presented. These are combined with results published elsewhere obtained concurrently with the proportional counter on the same satellite, thereby giving for the first time coincident observations of AM Her over the range 2 to 250 keV.
    Keywords: ASTRONOMY
    Type: NASA-TM-80238
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  • 8
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    High energy X-ray observations of CYG X-3 from from OSO-8: Further evidence of a 34.1 day period (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The X-ray source Cyg X-3 (=4U2030+40) was observed with the high energy X-ray spectrometer on OSO-8 for two weeks in 1975 and in 1976 and for one week in 1977. No change in spectral shape and intensity above 23 keV was observed from year to year. No correlation is observed between the source's intensity and the phase of the 34.1 day period discovered by Molteni, et al. (1980). The pulsed fraction of the 4.8 hour light curve between 23 and 73 keV varies from week to week, however, and the magnitude of the pulsed fraction appears to be correlated with the 34.1 day phase. No immediate explanation of this behavior is apparent in terms of previously proposed models of the source.
    Keywords: ASTRONOMY
    Type: NASA-TM-83862
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  • 9
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    High energy X-ray and radio studies of Scorpius X-1 (1978)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The results from extended high energy X-ray observations of Scorpius XR-1 from the OSO-8 satellite are reported here. The source was observed for a total of 15 days in 1975, 1977 and 1978. Simultaneous 10.7 GHz and 4.75 GHz radio data were obtained during the 1978 observation, and low energy X-ray data during the 1975 and 1978 observations. The data reveals a lack of any correlation between the high energy X-rays and the other energy ranges. A three standard deviation upper limit of 22% was obtained for any modulation of the high energy flux with the binary period. No high energy tail was observed at any time.
    Keywords: ASTRONOMY
    Type: NASA-TM-80298
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  • 10
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    The high-energy pulsed X-ray spectrum of HER X-1 as observed with OSO-8 (1978)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Her X-1 was observed from 1977 August 30 to September 10 using the High-Energy X-Ray Scintillation Spectrometer on board the OSO-8 satellite. The observation, during which the source was monitored continually for nearly an entire ON-state, covered the energy range from 16 to 280 keV. Pulsed flux measurements as a function of binary orbit and binary phase are presented for energies between 16 and 98 keV. The pulsed flux between 16 and 33 keV exhibited a sharp decrease following the fourth binary orbit and was consistent with zero pulsed flux thereafter. The pulsed spectrum was fitted with a power law, a thermal spectrum without features, and a thermal spectrum with a superposed gaussian centered at 55 keV. The latter fit has the smallest value of chi - squared per degree of freedom, and the resulting integrated line intensity is 1.5 superscript + 4.1 subscript - 1.4 x .001 photons s superscript-1 cm superscript-2 for a width of 3.1 superscript + 9.1 subscript -2.6 keV. This result, while of low statistical significance, agrees with the value observed by Trumper (1978) during the same On-state.
    Keywords: ASTRONOMY
    Type: NASA-TM-79692
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