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  • ASTROPHYSICS  (97)
  • SPACE SCIENCES
  • 1975-1979  (97)
  • 1970-1974
  • 1979  (97)
  • 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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    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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  • 7
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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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  • 8
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    Stellar model chromospheres. IX - Chromospheric activity in dwarf stars (1979)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: High-resolution Ca II K line profiles are used to model the upper photospheres and lower chromospheres of eight main-sequence stars ranging in spectral type from F0 to M0 and exhibiting different degrees of chromospheric activity. The model chromospheres are studied as a function of spectral type and activity for stars of similar spectral type in order to obtain evidence of enhanced nonradiative heating in the upper-photospheric models and in the ratio of minimum temperature at the base of the chromosphere to effective temperature, a correlation between activity and temperature in the lower chromospheres, and a correlation of the width at the base of the K-line emission core and at the K2 features with activity. Chromospheric radiative losses are estimated for the modelled stars and other previously analyzed main-sequence stars. The results obtained strengthen the argument that dMe flare stars exhibit fundamentally solar-type activity but on an increased scale.
    Keywords: ASTROPHYSICS
    Type: PB80-118086 , AD-A083858 , AFGL-TR-80-0106 , Astrophysical Journal; vol. 229
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  • 9
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    O VI absorption in interstellar cloud surfaces (1979)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: The velocity profiles of O VI absorption lines of 24 stars, observed in early Copernicus surveys, have been compared with the line profiles of Si III (1206.51 A) and N II (1083.99 A). The velocity structures of the O VI lines appear to be correlated with those of the material in the lower ionization stages. It is argued that the O VI absorption arises in the coronal gas of the conductive interface between hot gas, responsible for extended, soft X-ray emission, and cooler interstellar clouds. The velocity broadening of both sets of lines is attributed to motions of the cloud surfaces induced by pressure fluctuations in the interstellar medium.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 232
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  • 10
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    Interplanetary sector boundaries, 1971 - 1973 (1979)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Eighteen interplanetary sector boundary crossings observed at 1 AU by the magnetometer on the IMP-6 spacecraft are discussed. The events were examined on many different time scales ranging from days on either side of the boundary to high resolution measurements of 12.5 vectors per second. Two categories of boundaries were found, one group being relatively thin and the other being thick. In many cases the field vector rotated in a plane from one polarity to the other. Only two of the transitions were null sheets. Using the minimum variance analysis to determine the normals to the plane of rotation, and assuming that this is the same as the normal to the sector boundary surface, it was found that the normals were close to the ecliptic plane. An analysis of tangential discontinuities contained in 4-day periods about the events showed that their orientations were generally not related to the orientations of the sector boundary surface, but rather their characteristics were about the same as those for discontinuities outside the sector boundaries.
    Keywords: ASTROPHYSICS
    Type: NASA-TM-80565
    Format: application/pdf
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