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  • ASTROPHYSICS  (339)
  • 1985-1989
  • 1980-1984  (150)
  • 1975-1979  (189)
  • 1983  (150)
  • 1979  (121)
  • 1975  (68)
  • 1
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    Observations of NGC 7027 from 5.2 to 7.5 microns - The detection of Ni II and additional dust features (1983)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: NGC 7027 was observed with a multichannel grating spectrometer from 5.2 to 7.5 microns at a spectral resolving power of 120-200. Two new dust emission features are resolved at 5.62 and 6.95 microns, and for the first time the Ni II fine-structure line at 6.64 microns is detected. It is shown that a single molecular dust constituent might account for six of the nine observed dust features between 2 and 14 microns. The strength of the Ni II line indicates either that Ni is not depleted in the neutral gas, or that the line is formed at high density.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 274; 666-670
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  • 2
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    The C2H, C2, and CN electronic absorption bands in the carbon star HD 19557 (1983)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: Infrared spectrophotometry of the R-type carbon star HD 19557 is presented. Two unusual spectroscopic features are seen: a 3.1 micron band is lacking and a 2.8 micron band is present. Identifications are proposed for three previously unreported stellar absorption bands with electronic sequences of C2, CN, and C2H. The latter is proposed to be responsible for the 2.8 micron feature. The atmospheric structure of the star is studied with synthetic spectra, and an effective temperature between 2600 K and 3000 K is suggested. No SiC emission is seen at 11.3 microns, indicating that grain formation is not a viable process around the star. The lack of dust in R stars may suggest a salient difference between R and N types.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 270; July 1
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  • 3
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    The grains and gas in Comet Bowell 1980b (1983)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: The importance of coordinating different types of observations of a comet is illustrated in terms of spectral data on Comet Bowell. Photometric data in 1980 indicated that OH emissions were occurring when the comet was still more than 4 AU from the sun. Further measurements were arranged with the IUE satellite, the photoelectric scanner at Cerro Tololo and the IR telescope on Mauna Kea. Several sizes of diaphragms were used in order to estimate variations with respect to aperture. Calculations were made to quantify the wavelengths observed as a function of the grains' cross-sections. The OH emission was confirmed by the spectrographic and photometric data. It is suggested that sufficient dark materials are present on the cometary surface to have enhanced the absorption of solar radiation to levels sufficient for heating and dissociating surface ice particles.
    Keywords: ASTROPHYSICS
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  • 4
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    An ionization gradient across the front in M17 SW (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Measurements of forbidden Ne II lines at 12.8 microns and forbidden S IV at 10.5 microns are presented along a line through and perpendicular to the ionization front in M17 SW. These observations give evidence for ionization stratification within the front, with the most highly ionized material lying toward the east, opposite to the peak molecular emission and far-IR flux. This result supports the picture of M17 SW as a region where a molecular cloud is heated externally. The ionization equilibrium within the ridge and the nebular energetics suggest that the M17 H II region is largely excited by one or more nearby early O stars. The properties of the recently discovered radio point source in M17 are discussed.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 275; 130-134
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  • 5
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    SAS-2 high-energy gamma-ray observations of the Vela pulsar (1975)
    In:  Other Sources
    Details
    Publication Date: 2011-08-16
    Description: The Second Small Astronomy Satellite (SAS-2) high-energy (in excess of 35 MeV) gamma-ray telescope has detected pulsed gamma-ray emission at the radio period from PSR 0833-45, the Vela pulsar, as well as an unpulsed flux from the Vela region. The pulsed emission consists of two peaks following the single radio peak by about 13 ms and 48 ms. The luminosity of the pulsed emission above 100 MeV from Vela is about 0.1 that of the pulsar NP 0532 in the Crab nebula, whereas the pulsed emission from Vela at optical wavelengths is less than 0.0002 that from the Crab. The relatively high intensity of the pulsed gamma-ray emission, and the double peak structure, compared with the single pulse in the radio emission, suggest that the high-energy gamma-ray pulsar emission may be produced under different conditions from those at lower energies.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; 200; Sept. 1
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  • 6
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    Na-22, Ne-E, extinct radioactive anomalies and unsupported Ar-40 (1975)
    In:  Other Sources
    Details
    Publication Date: 2011-08-16
    Description: The possibility that the origin of extinct radioactivities depended on their living long enough for grains to form in the expanding nucleosynthetic envelope, rather than on their living long enough for meteorites to form, is examined. As an example, the interpretation of Na-22 as a detectable extinct radioactivity, with a half life of only 2.6 years, is explored and related to Ne-22 occurrence. Similar arguments involving He-4, Ar-40, K-40, K-41, and calcium, titanium, chromium, manganese, iron, nickel, and cobalt isotopes are briefly presented.
    Keywords: ASTROPHYSICS
    Type: Nature; 257; Sept. 4
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  • 7
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    Pioneer 9 and OGO 5 observations of an interplanetary multiple shock ensemble on February 2, 1969 (1975)
    In:  Other Sources
    Details
    Publication Date: 2011-08-16
    Description: A multiple shock system was observed upstream (0.13 AU) of the earth by Pioneer 9 on February 2, 1969. The same system was observed at earth by Ogo 5 and was reported separately in the literature. This paper compares the two sets of observations in still further detail. Both magnetic-field and plasma data are used in a least-squares best-fit method to compute the characteristics of the fast forward shock wave (Pioneer 9 only) and two fast reverse shock waves. Nearly all major features (shock, piston, and tangential discontinuity) retained their characteristics during the transit of the shock ensemble from Pioneer 9 to Ogo 5. The genesis of the ensemble is believed to be due to a complex stream-stream interaction. A substantial density increase (including a large rise of alpha/proton abundance) at Ogo 5, but unobserved at Pioneer 9, is explained by a sudden meridional shift to a flow from below the ecliptic plane while the streams were en route to earth. This study demonstrates a spatial and temporal plasma inhomogeneity which is superimposed on the persistent major features.
    Keywords: ASTROPHYSICS
    Type: Journal of Geophysical Research; 80; Aug. 1
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  • 8
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    High-energy gamma-ray results from the second small astronomy satellite (1975)
    In:  Other Sources
    Details
    Publication Date: 2011-08-16
    Description: Data are reported which were obtained with a high-energy (exceeding 35 Mev) gamma-ray telescope flown on the second Small Astronomy Satellite (SAS-2). The high-energy galactic gamma radiation is observed to dominate over the general diffuse radiation along the entire galactic plane, and its longitudinal and latitudinal distributions appear to be generally correlated with galactic structural features, particularly with arm segments. Principally on the basis of its angular distribution and magnitude, it is suggested that this radiation results primarily from cosmic-ray interactions with interstellar matter. A uniform celestial gamma radiation appears to have been detected; the form of its differential spectrum over the energy range from about 35 to 170 MeV is obtained, and a cosmological origin is suggested for this radiation. In addition to the general galactic emission, high-energy gamma radiation was detected from the Crab Nebula, Vela X, a general region toward the galactic center, and a region located a few degrees north of the galactic plane. Upper limits to the high-energy gamma ray fluxes are set for a number of localized sources.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; 198; May 15
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  • 9
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    An upper limit on interstellar C IV in the spectrum of gamma-2 Velorum (1975)
    In:  Other Sources
    Details
    Publication Date: 2011-08-16
    Description: An upper limit on the column density of C IV along the line of sight to gamma-2 Vel is derived from upper limits placed on the equivalent widths of the interstellar C IV doublet with rest wavelengths at 1548.20 A and 1550.77 A. A lower limit of 250,000 K is calculated for the electron temperature of O VI emitting regions by combining the C IV results with a measurement of the column density of interstellar O VI for the same star and using calculations for the relative ionization of some abundant elements as a function of electron temperature in a low-density plasma. Since gamma-2 Vel is in the central part of the Gum Nebula, the high temperature suggested by these results is shown to support the idea that a high-temperature phase of the interstellar medium, possibly maintained by supernova explosions, may exist.-
    Keywords: ASTROPHYSICS
    Type: The Observatory; 95; Oct. 197
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  • 10
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    Very long baseline interferometry at a wavelength of 3.4 mm (1983)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: The first detection of interference fringes by VLBI at a wavelength of 3.4 mm during observations of 3C84 are reported. The compact source in the nucleus of 3C84 was observed for a 9-hr period on the 485 km baseline between the Owens Valley Radio Observatory and the Hat Creek Observatory. The fringe data are given and the derivation of the correlated flux densities is described. The findings are discused in the context of previous obervations. The results demonstrate that there are no unforeseen technical difficulties associated with millimeter VLBI, and that the sensitivity of existing systems is sufficient to observe objects brighter than a few Jy. The observations are consistent with the millimeter wavelength radio structure of 3C84 being more compact than its centimeter wavelength structure.
    Keywords: ASTROPHYSICS
    Type: Nature (ISSN 0028-0836); 303; June 9
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