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  • ASTROPHYSICS  (171)
  • SPACE SCIENCES
  • 1975-1979  (171)
  • 1970-1974
  • 1979  (97)
  • 1978  (74)
  • 1
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    Stellar model chromospheres. XI - A survey of Ca II lambda 8542 line profiles in late-type stars of differing chromospheric activity (1979)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Keywords: ASTROPHYSICS
    Type: PB80-144215 , Astrophysical Journal Supplement Series; 41; Nov. 197
    Format: text
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  • 2
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    Balloon-borne ultraviolet stellar spectrograph. I - Instrumentation and observation. II - Highlights of first observational results (1979)
    In:  Other Sources
    Details
    Publication Date: 2011-08-17
    Description: A dual star-tracking system and a system including a telescope, an echelle spectrograph, and a SEC vidicon are the chief components of the Balloon-borne Ultraviolet Stellar Spectrograph (BUSS), which has flown four successful missions. The BUSS missions have yielded 81 spectra for 56 stars, recorded with a resolution of 0.1 A in the wavelength range from 2200 to 3400 A. BUSS observations include: profiles of Mg II lines indicating considerable mass flow in early-type supergiants; Mg II features suggesting a cool expanding outer shell above a hotter chromosphere; emission features in Zeta Tau (a shell star) indicating infalling material; and emission features of the Be star Phi Per suggesting mass outflow.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 230
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  • 3
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    A non-LTE treatment of beryllium lines - Misidentification of the solar Be I feature at 2650 A (1979)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: The formation of beryllium lines, with particular reference to the solar Be spectrum, is investigated in a non-LTE context with a 25-level model atom in which 15 levels are allowed to depart from LTE. In some transitions, particularly the Be I 2650-A line, the non-LTE effects can be quite dramatic, changing the deduced abundances by a factor of 4. Based on the non-LTE calculations and Copernicus observations of other stars, it is found that a solar spectral feature at 2650 A, previously identified by numerous investigators as a Be I line, cannot be produced by Be I. Non-LTE effects on the Be II 3131-A line, used for most Be abundance determinations in the literature, are small by comparison.
    Keywords: ASTROPHYSICS
    Type: Astronomical Journal; 84; Nov. 197
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  • 4
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    The brightness distribution of IRC +10216 at 11 microns (1979)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: The brightness distribution of IRC +10216 at a wavelength of 11 microns has been measured in detail by using spatial interferometer. This brightness distribution appears to have azimuthal symmetry; an upper limit of 1.1 may be set to the ellipticity at 11 microns if the object has a major axis oriented either along or perpendicular to the major axis of the optical image. The radial distribution shows both compact and extended emission. The extended component, which is due to thermal emission from circumstellar dust, contributes 91% of the total flux and has a 1/e diameter of 0.90 arcsec. The tapered shape of this component is consistent with a dust density dependence on the inverse square of radial distance. The compact component is unresolved (less than 0.2 arcsec in diameter) and represents emission from the central star seen through the circumstellar envelope.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 230
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  • 5
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    Orion's Cloak - A rapidly expanding shell of gas centered on the Orion OB1 association (1979)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: The structure of the interstellar gas surrounding the Orion OB1 association and the neighboring lambda Orionis association is detailed. UV absorption lime spectra of various ionization stages of C, N, Si and S in the directions of 12 stars were obtained by means of the spectrometer on board the Copernicus satellite. The presence of a shell of material surrounding the two associations and expanding at 100 to 120 km/sec, designated Orion's Cloak, was revealed, together with sporadically occurring higher column density matter at lower velocities. Results are interpreted to indicate the presence of a rapidly moving radiative shock outside the H II region of the association stars and inside this feature, a lower velocity, higher column density cloud which appears to be directly ionized by association stars. It is suggested that the gas features are caused by the effects of a recent supernova and of multiple supernovae, stellar winds and rocket-accelerated clouds in addition to stellar ionization.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 230
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  • 6
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    Interplanetary propagation of flare-associated energetic particles (1978)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: A propagation model which combines a Gaussian profile for particle release from the sun, with interplanetary particle densities predicted by focused diffusion, was proposed to explain the propagation history of flare associated energetic particles. This model, which depends on only two parameters, successfully describes the time-intensity profiles of 30 proton and electron events originating from the western hemisphere of the sun. Generally, particles are released from the sun over a finite interval. In almost all events, particle release begins at the time of flare acceleration.
    Keywords: ASTROPHYSICS
    Type: NASA-TM-79534
    Format: application/pdf
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  • 7
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    High-pressure transition regions in stellar model chromospheres (1979)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: The implications of recent ultraviolet observations of stellar transition-region lines for calculations of the Ca II and Mg II resonance lines are investigated. It is found that the adoption of high transition-region pressures for stars with active chromospheres, such as Lambda And and Alpha Aur, can be consistent with observed Ca II fluxes, contrary to the results obtained by Kelch et al. (1978) for Alpha Aur. Furthermore, the adoption of the high-pressure models removes a long-standing difficulty in the line profile calculations, since the deep central absorption present in earlier calculations is less pronounced or absent, in closer agreement with observations. The apparent contradiction between these models and the recent density diagnostic of Doschek et al. (1978) is also discussed.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 233
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  • 8
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    The velocity distribution of interstellar gas observed in strong UV absorption lines (1978)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: Observations of three strong interstellar UV absorption lines of N I (1199 A), N II (1083 A), and Si III (1206 A) in 47 stars of widely varying distance and a variety of spectral types are analyzed to obtain a velocity distribution function for the interstellar gas. A technique based on the maximum and minimum velocities observed along a line of sight is adopted because of heavy line blending, and results are discussed for both power-law and exponential distribution functions. The expected distribution of radiative-phase supernova remnants (SNRs) in the interstellar medium is calculated as a function of SNR birthrate and of the interstellar density in which they evolve. The results are combined with observed distance estimates, and it is shown that an interstellar density in excess of 0.1 per cu cm would be required to keep the SNRs sufficiently confined so that their cross sections are consistent with the observed number of components. The alternative possibility is considered that SNRs do not enter the radiative phase before escaping from the Galaxy or colliding with neighboring remnants.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 223
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  • 9
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    Intermediate-velocity gas in the local interstellar medium (1978)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: Scans of interstellar ultraviolet absorption lines of N I, N II, and Si III for 17 stars are combined with previously published data for 30 stars. The extremal velocities at which detectable absorption occurs are tabulated, and it is shown that these are correlated for the three species. The data suggest that intermediate-velocity gas (20 to 60 km/s), best known from Na I and Ca II absorption, contains both neutral and ionized hydrogen. Features characteristic of intermediate-velocity isothermal shocks (greater than 60 km/s) are conspicuously rare. The intermediate-velocity gas may be in the form of clouds containing both H I and H II regions or of radiative shocks propagating in the interstellar medium; in the latter case the gas should be detectable in H-alpha emission.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 220
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  • 10
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    NH3 in IRC +10216 (1979)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: Ammonia has been detected in the circumstellar envelope of IRC +10216 by means of three infrared absorption lines in the nu-2 band around 950 kaysers. The profiles are well resolved at a resolution of 0.22 km/s and show that most of the circumstellar gas is accelerated to expansion velocities around 14 km/s within a few stellar radii. The observed ammonia requires a rotational temperature between 400 and 700 K, an H2 density between 100 million and 10 billion per cu cm, and an NH3 column density of 10 to the 17th per sq cm. The H2 density indicates that the mass of the circumstellar envelope within a 1 arcsec radius is about 0.1 solar mass.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 229
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