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  • ASTROPHYSICS  (63)
  • 1
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    Search for interstellar superheavy hydrogen (1982)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: Models for fundamental physical interactions allow for the existence of stable or nearly stable elementary particles much heavier than the proton. Stellar spectra were searched for a positively charged superheavy particle, X(+), which, with a bound electron, should appear as apparently superheavy neutral hydrogen in the interstellar medium. An upper limit for the abundance of X relative to normal hydrogen in the line of sight toward the bright star gamma Cassiopeiae is 2 x 10 to the -8th.
    Keywords: ASTROPHYSICS
    Type: Science; 216; Apr. 2
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  • 2
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    Observations of interstellar zinc (1982)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: IUE observations toward 10 stars have shown that zinc is not depleted in the interstellar medium by more than a factor of two, suggesting that its abundance may serve as a tracer of the true metallicity in the gas. A result pertinent to the history of nucleosynthesis in the solar neighborhood is that the local interstellar medium has abundances that appear to be homogeneous to within a factor of two, when integrated over paths of about 500 pc.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 254
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  • 3
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    Synthesis of Data on the Local Interstellar Medium (1984)
    In:  CASI
    Details
    Publication Date: 2014-09-16
    Description: While no completely definitie picture of the local interstellar medium can be presented yet, some general conclusions can be drawn. New UV results are collated with published results to help state the physical properties of the gas. A morphological view of the local medium is given.
    Keywords: ASTROPHYSICS
    Type: NASA. Goddard Space Flight Center Local Interstellar Medium, No. 81; p 51-59
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  • 4
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    Gas in the galactic halo (1982)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The evidence that gas exists in the halo of the Galaxy is examined. The likely properties of halo gas intervening between QSOs and the Galaxy are extracted from observations of the galactic halo. The available data discussed include 21-cm observations, optical absorption lines, ultraviolet lines, and X-ray observations. The possible existence of a cosmic ray halo is assessed, and the relationship of galactic size to the extent of the halo is examined. The main physical constraints on the gas in the halo are detailed, including the radiation field, particle density, temperature, mass in the halo gas, and abundances. Models for the gas in the halo are summarized. It appears that the distribution of gas in the galactic halo is an expanded disk not more than 10 kpc thick. At low column densities, the Galaxy could extend out to several times the Holmberg radius. The disk may be photoionized on the outside by the QSO background radiation.
    Keywords: ASTROPHYSICS
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  • 5
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    Probe of the Nearby Interstellar Medium by the Vacant Line of Sight to Beta Cma (1984)
    In:  CASI
    Details
    Publication Date: 2014-09-16
    Description: The line of sight to Beta CM a was probed by Copernicus observations. This particular line of sight is remarkable for the low mean densities. The density was found to be bar N sub H approximately .002/cu cm. Two separate regions were distinguished: (1) A local nearby HI region extends over a few parsecs from the Sun with a density of the order of 0.1/cu cm and a temperature of 11000 to 12500 K; (2) An HII region lies somewhere beyond the HI region and is spread over about 60pc. Its total hydrogen mean density is of the same order as the HI region, i.e., of approximately 0.1 cu cm and it contains only elements in low ionization state. All the ata are coherent with the picture of a cloud in ionization equilibrium at T approximately 23000 deg K.
    Keywords: ASTROPHYSICS
    Type: NASA. Goddard Space Flight Center Local Interstellar Medium, No. 81; p 80-83
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  • 6
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    Optical Observations of Nearby Interstellar Gas (1984)
    In:  CASI
    Details
    Publication Date: 2014-09-16
    Description: Observations indicated that a cloud with a heliocentric velocity of approximately -28 km/s and a hydrogen column density that possibly could be on the order of, or greater than, 5 x 10 to the 19 power/square cm is located within the nearest 50 to 80 parsecs in the direction of Ophiuchus. This is a surprisingly large column density of material for this distance range. The patchy nature of the absorption from the cloud indicates that it may not be a feature with uniform properties, but rather one with small scale structure which includes local enhancements in the column density. This cloud is probably associated with the interstellar cloud at about the same velocity in front of the 20 parsec distant star alpha Oph (Frisch 1981, Crutcher 1982), and the weak interstellar polarization found in stars as near as 35 parsecs in this general region (Tinbergen 1982). These data also indicate that some portion of the -14 km/s cloud also must lie within the 100 parsec region. Similar observations of both Na1 and Ca2 interstellar absorption features were performed in other lines of sight. Similar interstellar absorption features were found in a dozen stars between 20 and 100 parsecs of the Sun.
    Keywords: ASTROPHYSICS
    Type: NASA. Goddard Space Flight Center Local Interstellar Medium, No. 81; p 113-116
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  • 7
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    On the possibility of detecting very hot gas through absorption-line studies (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The possibility of detecting hot (T greater than or approximately equal to 10 to the 6th K) diffuse interstellar and intergalactic gas through absorption-line studies is assessed. Optical studies of semiforbidden lines are shown to be just beyond feasibility. X-ray absorption-line studies are concluded to be within the capability of future soft X-ray spectrographs, however. In particular, it is shown that the Bragg crystal spectrometer aboard Einstein could possibly have been used to detect O VII and O VIII lines against the Crab if they are present at plausible levels. Improvement of instrument parameters by only a small factor could make this the most important method available for studying hot interstellar, galactic halo and possibly even intergalactic gas.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 264
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  • 8
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    The filaments of NGC 1275 - A collision between a galaxy and an accretion flow? (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Morphological evidence is presented (in the form of 3-A-bandpass Fabry-Perot images made with a CCD camera) that the two bright emission-line systems seen toward the galaxy NGC 1275 arise from a high-velocity impact of a foreground galaxy upon the accretion flow of gas cooling in the center of the Perseus cluster. The uniquely high optical-line luminosity of NGC 1275, in comparison with other central galaxies in clusters observed to have cooling flows, may be explained by energy deposited during the collision. Using additional information from 21-cm and extinction measurements, a rough model of the interaction is developed. Problems remain with this model - such as the likelihood of a gas-rich system penetrating to the cluster center. The kinematic structure of the optically emitting gas shows additional complex structure near the nucleus of NGC 1275.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters to the Editor (ISSN 0004-637X); 275; L27-L31
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  • 9
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    Interstellar abundances of oxygen and nitrogen (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Neutral nitrogen and oxygen column densities or limits are derived for 53 path lengths through the diffuse interstellar medium and compared with column densities of neutral hydrogen. For neither N nor O is a systematic increase of depletion found as reddening increases. The value found for forbidden O/N is 8, and the abundances of N and O are both between 40% and 70% of the solar values. Implications of these results for models of interstellar grains are briefly discussed.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 266
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  • 10
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    The detection of interstellar fluorine in the line of sight toward Delta Scorpii (1981)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The resonance line of F I at 954.825 A is detected in the interstellar spectra of Delta Sco, and possibly Delta Ori, and upper limits are obtained toward five other stars. It is noted that the equivalent width for Delta Sco of 10.9(+4.5, -3.1) in milliangstroms corresponds to a column density of 1.52(+0.60, -0.43) x 10 to the 13th/sq cm and a depletion of -0.53(+0.15, -0.14) dex. For the other lines of sight, depletions of at least 0.1-0.5 dex are inferred. The results are discussed in the context of current theories of the depletion process.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 247
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