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  • ASTROPHYSICS  (35)
  • Astronomy  (1)
  • 1
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    The HRS GTO program to study the neutral hydrogen column density and D/H ratio in the local interstellar medium (1986)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Theoretical line profiles are presented that demonstrate why 100,000 spectral resolution and high S/N are needed to derive accurate column densities from spectral lines that lie close to the flat part of the curve of growth and may contain multiple velocity components. The aim of the Space Telescope high-resolution-spectrograph observing program is to obtain column densities in the hydrogen and deuterium Lyman alpha lines along a variety of lines of sight within and extending beyond the local cloudlet, in which the sun is located near an edge. The broad chromospheric Lyman alpha emission lines of late-type stars are used as background sources against which to measure the interstellar absorption features. Profiles of interstellar absorption features in Mg II and Fe II lines will be obtained to derive the broadening parameter and/or identify possible multiple velocity components in the lines of sight.
    Keywords: ASTROPHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 6; 2, 19; 91-94
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  • 2
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    Observed properties of interstellar dust (1979)
    In:  Other Sources
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    Publication Date: 2011-08-17
    Description: Recent information on the observed properties of interstellar dust is reviewed, with an attempt made to clarify some of the observational uncertainties associated with obtaining dust parameters. Attention is given to interstellar extinction, the interstellar dust distribution, the dust-to-gas ratio, and light scattering by dust grains. Interstellar polarization is also examined, along with heavy-element depletion in the interstellar medium, thermal emission from interstellar dust grains, diffuse interstellar features, and the composition and origin of interstellar grains.
    Keywords: ASTROPHYSICS
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  • 3
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    Future Studies of the Local Interstellar Medium with Space Telescope and Columbus (1984)
    In:  CASI
    Details
    Publication Date: 2014-09-16
    Description: The spectrographs aboard Space Telescope and Columbus which will provide important new information about the interstellar medium in the immediate vicinity of the sun are described. The space telescope's highest resolution is adequate to define the multicomponent nature of interstellar absorption lines and to measure thermal line widths exceeding 3 km/s. The Columbus spacecraft will contain spectrographs capable of resolutions of 3 x 10 to the 4th power between 912 and 1200 A and 500 between 100 and 900 A. In the short wavelength region, lines of He I and II, are observable. If the 3 x 10 to the 4th power resolution spectrograph provides extended wavelength coverage to 770 A, lines of Ne VIII which are expected from 8 x 10 to the 5th power K gas are accessible. The ST HRS and Columbus spectrographs enable the study of a wide range of problems relating to cold, warm, and hot gas in the local ISM.
    Keywords: ASTROPHYSICS
    Type: NASA. Goddard Space Flight Center Local Interstellar Medium, No. 81; p 333-343
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  • 4
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    Ultraviolet absorption by interstellar gas at large distances from the galactic plane (1981)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Eighteen high dispersion International Ultraviolet Exploration spectra of 6 stars in the large magellanic cloud (LMC) 3 stars in the small magellanic cloud (SMC) and 2 foreground stars were studied. Fourteen spectra cover the wavelengths lambda 1150-2000 A and 4 cover lambda 1900-3200 A. All the Magellanic Cloud star spectra exhibit exceedingly strong interstellar absorption lines due to a wide range of ionization stages at galactic velocities and at velocities associated with the LMC or SMC. The analysis is restricted to the Milky Way absorption features. Toward the LMC stars, the strong interstellar lines have a positive velocity extension, which exceeds the extension recorded toward the SMC stars. The most straightforward interpretation of these velocity extensions is obtained by assuming that gas at large distances away from the plane of the galaxy participates in the rotation of the galaxy as found in the galactic disk.
    Keywords: ASTROPHYSICS
    Type: NASA. Goddard Space Flight Center The Universe at Ultraviolet Wavelengths: The First Two Yrs. of Intern. Ultraviolet Explorer; p 611-612
    Format: application/pdf
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  • 5
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    Ultraviolet absorption by highly ionized halo gas near the Galactic center (1985)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Initial results are presented for a program to survey highly ionized gas in the Milky Way disk and halo. High-resolution IUE (International Ultraviolet Explorer) far-UV spectra were obtained for 12 stars at galactocentric distances less than 6 kpc. The stars are 0.7-2.2 kpc away from the plane. Most of the spectra contain exceedingly strong and broad interstellar absorption lines of weakly and highly ionized atoms. In addition to the normally strong lines of Si IV and C IV, strong interstellar NV lines have been detected in the spectra of eight stars. The detection of NV absorption (amounting to more than 10 times the predicted NV) provides an important new constraint on models for the origin of Galactic halo gas. A Galactic fountain operating in the presence of known UV and EUV radiation might explain the observations.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters to the Editor (ISSN 0004-637X); 295; L9-L12
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  • 6
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    Ultraviolet interstellar absorption toward HD 5980 in the Small Magellanic Cloud (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Individual high-dispersion International Ultraviolet Explorer (IUE) spectra of extragalactic stars are noisy because of the long exposure times required and the inherent limitations of the IUE detectors. A program has, therefore, been undertaken to obtain multiple ultraviolet spectra of the brightest Magellanic Cloud stars in order to produce composite spectra with higher signal-to-noise ratios than in individual spectra. The present investigation is concerned with results for HD 5980. The target star, HD 5980, is one of the brightest extragalactic far-ultraviolet sources in the sky. HD 5980 is located in the northeast quadrant of NGC 346, the largest H II region and OB star cluster in the SMC. The analysis of the interstellar line spectrum of HD 5980 provides a number of conclusions about the complex absorption characteristics of the interstellar gas toward the SMC.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 267
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  • 7
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    Peculiar ultraviolet interstellar extinction (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: In connection with investigations of the physical characteristics of interstellar dust, a study of objects with peculiar extinction might provide new insights about the composition, size distribution, formation, and destruction of the particulate matter. Meyer and Savage (1981) have found that the dust toward many stars exhibits peculiar UV extinction. The present investigation is concerned with International Ultraviolet Explorer (IUE) spectrophotometric measurements for a sample of stars judged by Meyer and Savage to have highly anomalous UV extinction as inferred from the broad-band Astronomical Netherlands Satellite (ANS) data. The reported IUE measurements provide the opportunity to determine if the ANS photometry measurements of Meyer and Savage are anomalous because of peculiar extinction.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 266
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  • 8
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    Interstellar abundances of oxygen and nitrogen (1983)
    In:  Other Sources
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    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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  • 9
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    Ultraviolet absorption by interstellar gas at large distances from the galactic plane (1981)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Eighteen high-dispersion IUE spectra of six stars in the Large Magellanic Cloud, three stars in the Small Magellanic Cloud, and two foreground stars were analyzed. Fourteen spectra cover the wavelengths 1150-2000 A, and four cover 1900-3200 A; the velocity resolution is about 25 km/s. All the Magellanic Cloud spectra exhibit very strong interstellar absorption lines due to a wide range of ionization stages at galactic velocities and at velocities associated with the IMC or SMC. The observational results are related to current theoretical ideas about the origin and physical state of gaseous galactic halos; the analysis is restricted to the Milky Way absorption features.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 243
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  • 10
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    Copernicus observations of the N v resonance doublet in 53 early-type stars (1982)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: UV spectra in the wavelength interval 1170-1270 A are presented for 53 early-type stars ranging in spectral type from O6.5 V to B2.5 IV. The sample includes four Wolf-Rayet stars, seven known Oe-Be stars, and six galactic halo OB stars. A qualitative analysis of the stellar N v doublet reveals that: (1) N v is present in all stars hotter and more luminous than type B0 for the main sequence, B1 for giants, and B2 for supergiants; (2) shell components of N v and an unidentified absorption feature at 1230 A are present in about half of the stars; (3) the column density of N v is well correlated with bolometric luminosity over the spectral range O6 to B2; and (4) the ratio of emission to absorption equivalent width is a factor of 2 smaller in the main sequence stars than in supergiants, which suggests that the wind structure changes as a star evolves. For several stars, this ratio is too small to be explained by traditional wind models.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal Supplement Series; 48; Mar. 198
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