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  • ASTROPHYSICS  (1,475)
  • SPACE SCIENCES  (1,204)
  • 1995-1999  (67)
  • 1985-1989  (778)
  • 1980-1984  (589)
  • 1970-1974  (1,245)
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  • 11
    Publication Date: 2019-06-28
    Description: The Einstein Imaging Particle Counter observed a major X-ray flare in its entirety during a 5-hr period of simultaneous observations, with the IUE, of the dM5e flare star Proxima Centauri in August, 1980. The detailed X-ray light curve, temperature determinations during various intervals, and UV line fluxes obtained before, during, and after the flare indirectly indicate a 'two-ribbon flare' prominence eruption. The calculated ratio of coronal to bolometric luminosity for the event is about 100 times the solar ratio. The Proxima Cen corona is analyzed in the context of static loop models, in light of which it is concluded that less than 6% of the stellar surface seems to be covered by X-ray emitting active regions.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 267
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  • 12
    Publication Date: 2019-06-28
    Description: The 1.24-sec pulsations of Her X-1 in the energy range 13-75 keV have been analyzed in data obtained from the UCSD/MIT experiment on HEAO 1 during observations of the source on three dates in February 1978 and three in August 1978. Observational results are (1) the main pulse broadens somewhat with increasing energy; (2) the pulsation light curve undergoes pronounced changes at the leading edge of the main pulse from day to day; (3) spectral hardening within the main pulse is confirmed; (4) a 40-60 keV spectral feature in the spectrum is confirmed; (5) this feature is resolved, the pulse width broadening is greater than 20%, and its centroid varies with pulsation phase; and (6) the 13-75 keV spectrum does not noticeably vary from day to day, except for an overall intensity factor. Some implications of these results for the prevailing models of Her X-1 and the HZ Her-Her X-1 system are briefly discussed.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 240
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  • 13
    Publication Date: 2019-06-28
    Description: X-ray spectra of GX 339-4 measured on three occasions in 1977 and 1978 are presented. These are the first reported measurements above 10 keV. The spectra can be described as the superposition of a soft component, which is dominant below about 20 keV, and a hard component at higher energy. Simultaneous measurements at lower energy show that the soft component vanished during the observation in early 1978. The behavior of these two components is similar to that of the spectrum of Cygnus X-1; this reinforces the previously noted resemblance in rapid X-ray variability.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 262
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  • 14
    Publication Date: 2019-06-28
    Description: A new method to attack the question of the 'missing' globular clusters in the bulge of M31 is used. Image-processing techniques were used on 13 videocamera fields to obtain an accurate photometric census of stellar objects in M31's bulge down to a limiting B magnitude of 21. This luminosity distribution is compared with the Bahcall-Soneira model of galactic foreground stars. A statistically significant excess of bright images in the luminosity range of globular clusters at M31's distance is found. If the optical candidates considered prove to be globular clusters, they would double the number of known globular clusters in the surveyed region. The colors of a subsample of the candidates are the same as those of the known globular clusters. It is concluded that the previously observed flattening away from a de Vaucouleurs law in the radial distribution of M31 may be an observational selection effect. As an offshoot of this analysis, no evidence is found for very luminous stars in the inner bulge of M31. The lack of such stars indicates that there has not been active star formation (with a normal IMF) in the recent past. Coupled with the existence of many planetary nebulae in the bulge, this may strengthen the case for a galactic wind in M31's bulge.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 290; 140-153
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  • 15
    Publication Date: 2019-06-27
    Keywords: SPACE SCIENCES
    Type: Earth and Planetary Science Letters; 17; Dec. 197
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  • 16
    Publication Date: 2019-06-27
    Description: Preliminary designs for unmanned orbital exploration missions to Jupiter are examined, and the operational options and systems requirements consistent with the major scientific goals of the mission are summarized. In general, each mission design provides repeated measurements of the interaction of Jupiter with the solar media, encounters at least two Galilean satellites with multiple encounters with at least one satellite at distances which allow photography with resolutions of at least 10 km; provides at least 10 orbital maps of the field and particle environment surrounding Jupiter, and provides synoptic observations of Jupiter over a range of wavelengths and various degrees of photographic coverage with resolutions of 300 to 30 km.
    Keywords: SPACE SCIENCES
    Type: NASA-TM-X-2565 , A-4276
    Format: application/pdf
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  • 17
    Publication Date: 2019-06-27
    Description: Petrological, mineralogical, and chemical investigations of the B-1 Luna 16 sample have revealed that the sample is a fine-grained ophitic basalt which is distinguished from the Apollo samples by containing a single pyroxene, an ilmenite content intermediate to that of the Apollo samples, and subequal amounts of pyroxene and plagioclase. It is also distinguished by a high Sr content and a high K/U value.
    Keywords: SPACE SCIENCES
    Type: Earth and Planetary Science Letters; 13; Jan. 197
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  • 18
    Publication Date: 2019-06-27
    Description: The unique properties of the Mariner 10 radio system, and the preliminary scientific results obtained from the analysis of the radio signals are described. In the normal two-way communication mode, a command- and range-modulated 2115-MHz signal is transmitted to the spacecraft for reception on its omnidirectional antenna. As implemented for Mariner 10, the dual-frequency system has proven fully capable of performing interplanetary columnar electron content measurements while achieving the prime goals of the celestial mechanics and radio science team. The determination of the mass and gravitational potential of Venus is one of the major objectives of the radio science experiments. Information on Venus's atmosphere was deduced from analysis of the radio signals during occultation. Open-loop receiver differential Doppler data were used to measure the nightside and dayside ionospheres of Venus.
    Keywords: SPACE SCIENCES
    Type: Science; 183; Mar. 29
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  • 19
    Publication Date: 2019-06-27
    Description: This manual is a guide for using a computer program which calculates time optimal trajectories for high-and low-thrust geocentric transfers. Either SEP or NEP may be assumed and a one or two impulse, fixed total delta V, initial high thrust phase may be included. Also a single impulse of specified delta V may be included after the low thrust state. The low thrust phase utilizes equinoctial orbital elements to avoid the classical singularities and Kryloff-Boguliuboff averaging to help insure more rapid computation time. The program is written in FORTRAN 4 in double precision for use on an IBM 360 computer. The manual includes a description of the problem treated, input/output information, examples of runs, and source code listings.
    Keywords: SPACE SCIENCES
    Type: NASA-CR-139038 , R-827
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  • 20
    Publication Date: 2019-06-28
    Description: On five occasions in 1977 and 1978, Cygnus X-1 was observed using the low-energy detectors of the UCSD/MIT Hard X-ray and Low-Energy Gamma Ray experiment on the HEAO 1 satellite. Rapid (times between 0.08 and 1000 sec) variability was found in the 10-140 keV band. The power spectrum was white for frequencies between 0.001 and 0.05 Hz and was proportional to the inverse of the frequency for frequencies between 0.05 and 3 Hz, indicating correlations on all time scales less than approximately 20 s. The shape of the energy spectrum was correlated with intensity; it was harder at higher intensity. If the emission is produced by Comptonization of a soft photon flux in a hot cloud, the heating of the cloud cannot be constant; it must vary on time scales up to approximately 20 s. A variable accretion rate could cause the observed effects.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 246
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