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  • ASTROPHYSICS  (20)
  • 1980-1984  (20)
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Years
Year
  • 1
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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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  • 2
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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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  • 3
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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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  • 4
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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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  • 5
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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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  • 6
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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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  • 7
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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
    Format: text
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  • 8
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    Ultraviolet absorption by highly ionized atoms in the Orion Nebula (1982)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The International Ultraviolet Explorer was used to obtain high-resolution, far-UV spectra of theta 1 A, theta 1 C, theta 1 D, and theta 2 A Orionis. The interstellar absorption lines in these spectra are discussed with an emphasis on the high-ionization lines of C IV and Si IV. Theta 2 A Ori has interstellar C IV and Si IV absorption of moderate strength at the velocity found for normal H II region ions. Theta 1 C Ori has very strong interstellar C IV and Si IV absorption at velocities blueshifted by about 25 km/s from that found for the normal H II region ions. The possible origin of the high-ionization lines by three processes is considered: X-ray ionization, collisional ionization, and UV photoionization. It is concluded that the C IV and Si IV ions toward theta 2 A and theta 1 C Ori are likely produced by UV photoionization of surrounding nebular gas. In the case of theta 1 C Ori, the velocity shift of the high-ionization lines may be produced through the acceleration of high-density globules in the core of the nebula by the stellar wind of theta 1 C Ori.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 255
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  • 9
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    Ultraviolet interstellar extinction toward stars in the Orion Nebula and toward HD 147889 (1981)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The International Ultraviolet Explorer (IUE) was used to obtain low resolution absolute ultraviolet energy distributions for the four Trapezium stars Theta(1) Orionis A, B, C, and D, Theta(2) Orionis A and B, HD 147889, and several unreddened standard stars. The observations for Theta(1) Orionis B reveal a peculiar extended object. The measurements for the rest of the stars were used to derive UV extinction curves. The derived curves are very different from the average galactic curve. The curves for the Orion stars all exhibit smaller than normal middle and far-UV extinctions. Although a 2175 A feature is present, its strength, when normalized to E(B-V), is smaller than in the average galactic curve. In contrast, the curve for HD 147889 has a pronounced 2175 A feature followed by smaller than normal extinction for an inverse wavelength between 5 and 7 per micron.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 249
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  • 10
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    Evidence for hot gaseous coronae around the Magellanic Clouds (1980)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: High-dispersion IUE far-UV spectra were obtained for five stars in the LMC and two stars in the SMC. At Magellanic Cloud velocities, all the spectra exhibit very strong interstellar lines of Al III, Si IV, and C IV, in addition to the usual lower ionization stage lines associated with H I region absorption. In two stars interstellar N V is also detected at the 50 mA level. From a consideration of the strength, width, and radial velocity of these high ionization stage lines, it is argued that regions of hot halo gas have probably been detected in front of the Magellanic Clouds. The regions detected exhibit absorption characteristics very similar to that of the Milky Way corona described previously by Savage and de Boer (1979). A cloud detected in the line of sight to HD 5980 in the SMC at a radial velocity of 300 km/s is of unknown origin.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 238
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