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  • 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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    Pruning the Lyman alpha forest of Q1331+170 (1993)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: A multitude of absorption lines seen shortward of QSO Ly-alpha emission, that cannot be traced to heavy element absorption systems, are assumed to be Ly-alpha lines arising in intervening clouds. Studies of these Ly-alpha clouds, typically done at 1 A or lower resolution, have shown N(H1) approximately equal to 10(exp 13) - 10(exp 17) sq cm and b approximately equal to 35 km/s. Sargent et al 1980, on the basis of a flat pair velocity correlation function (PVCF), argued that these clouds are intergalactic. But Crotts 1989 showed that the strong Ly-alpha lines are spatially clustered. High resolution studies of Webb 1987 and Rauch et al 1992 also report some evidence for weak clustering, but overall such high resolution studies have been rare. A study of the Ly-alpha forest of Q1331 + 170 over x(sub abs) = 1.60 - 2.19 based on 18 km/s resolution data at S/N approximately equal to 15, with metal-line deblending incorporated.
    Keywords: ASTROPHYSICS
    Type: NASA. Ames Research Center, The Evolution of Galaxies and Their Environment; p 141-142
    Format: application/pdf
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  • 5
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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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  • 6
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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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  • 7
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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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  • 8
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    Fragmentation of cosmic-string loops (1989)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The fragmentation of cosmic string loops is discussed, and the results of a simulation of this process are presented. The simulation can evolve any of a large class of loops essentially exactly, including allowing fragments that collide to join together. Such reconnection enhances the production of small fragments, but not drastically. With or without reconnections, the fragmentation process produces a collection of nonself-intersecting loops whose typical length is on the order of the persistence length of the initial loop.
    Keywords: ASTROPHYSICS
    Type: NASA-CR-184892 , NAS 1.26:184892 , FERMILAB-PUB-89/32-A
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  • 9
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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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  • 10
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    Interstellar clouds near the sun (1986)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Present knowledge concerning interstellar clouds near the sun is reviewed. The distribution and chracteristics of this interstellar dust and gas are described, and interstellar wind flowing through the solar system is discussed. Evidence is presented for a flow of more distant interstellar material past the solar system. Possible effects of an encounter between the solar system and a cloud core embedded in this low-density flow are examined. It is likely that the solar system is heading for condensations within 100 pc and that encounters may occur in the next 0.1 to 1 Myr. Such encounters could trigger global weather effects, including surface cooling and increased precipitation.
    Keywords: ASTROPHYSICS
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