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  • 1
    Electronic Resource
    Electronic Resource
    Large-Scale Motions of Ionized Calcium in the Atmosphere of A Giant Star (1952)
    [s.l.] : Nature Publishing Group
    Nature 169 (1952), S. 990-992 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] THE star 31 Cygni, magnitude 4-0, was announced1 in 1898 as having a composite spectrum, and was later found by W. W. Campbell2 to be a spectroscopic binary. In 1936 W. H. Christie3 obtained an approximate spectrographic orbit for the brighter component, and in 1944 Miss Vinter Hansen4 published a ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/169990a0
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  • 2
    Electronic Resource
    Electronic Resource
    An Astronomical Rescue (1995)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Astronomy and Astrophysics 33 (1995), S. 1-18 
    Details
    ISSN: 0066-4146
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.aa.33.090195.000245
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  • 3
    Electronic Resource
    Electronic Resource
    Measurements of the Gegenschein from Space (1971)
    [s.l.] : Nature Publishing Group
    Nature 232 (1971), S. 323-324 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Ground-based observations are weakened by atmospheric extinction and diluted by the upper atmosphere airglow and light scattered in the Earth's lower atmosphere. Measurements of the gegenschein from above the Earth's atmosphere avoid the difficulties of these atmospheric effects. Accordingly, an ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/232323a0
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  • 4
    Electronic Resource
    Electronic Resource
    Theoretical models of planetary nebulae II: NGC 4361, an unusual high-excitation nebula (1979)
    Springer
    Astrophysics and space science 64 (1979), S. 347-357 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract NGC 4361 is an extremely high excitation, low-density, very inhomogeneous nebula. New spectroscopic data obtained with the Anglo-Australian telescope, together with published material, have been re-interpreted with the aid of theoretical nebular models that permit an estimation of its chemical composition. Helium may be slightly more abundant than in an ordinary planetary, although this is far from certain. Nitrogen, oxygen, and neon appear to be deficient by a factor of 3 or 4 compared with an ordinary planetary nebula. Argon is likewise deficient but the factor is more difficult to establish, partly because of the nebular inhomogeneity and partly because of uncertainties in cross-sections. THe nebula is material bounded and optically thin in the hydrogen continuum. In contrast to other high-excitation nebulae, the low-excitation condensations appear to have been destroyed by penetration of ionizing radiation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00639514
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  • 5
    Electronic Resource
    Electronic Resource
    Theoretical models of planetary nebulae (1980)
    Springer
    Astrophysics and space science 72 (1980), S. 203-210 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Introduction of the O+++H0→O++H+ charge exchange rate suggested by Butler, Bender and Dalgarno leads to theoretical nebular models that differ from those previously computed in several important respects. Different elemental abundances, ‘bluer’ central star energy distributions, and truncated (material limited) models are required. If the argon abundance is fixed from the λ 7135 [Ariii] line intensity, λ 4740 [Ariv] is invariably predicted to be much too strong. Better atomic parameters, together with improved charge exchange rates for other ions, and more accurate dielectronic recombination rates may alleviate the situation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00642179
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  • 6
    Electronic Resource
    Electronic Resource
    Theoretical models of planetary nebulae (1978)
    Springer
    Astrophysics and space science 59 (1978), S. 91-108 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Sets of theoretical models of spherically symmetrical gaseous nebulae are calculated for a fixed chemical composition and with central star, energy distributions given by Cassinelli (1971) and by Kunasz, Mihalas and Hummer (1975). A central region of constant densityN H=100 cm−3 is surrounded by a broken shell consisting of zones of different density and optical thickness. It is found that for a fixed chemical composition and central star flux, a considerable range can be found in the emitted fluxes of certain lines such as λ4686 which are often used to fix the level of excitation of a nebula. Although it is possible to produce models yielding a variety of nebular line ratios in this way, these truncated inhomogeneous shell models have not reproduced the integrated spectra of nebulae that simultaneously show extreme features of high and low excitation with great strength-e.g. [Nii], [Oii] and λ4686 Heii.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00651044
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  • 7
    Electronic Resource
    Electronic Resource
    Theoretical models of planetary nebulae (1982)
    Springer
    Astrophysics and space science 83 (1982), S. 225-238 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Theoretical models are calculated for 15 planetary nebulae of medium-to-high excitation, following procedures previously described. Initial stellar energy distributions are adopted from Cassinelli (1971), but are subsequently modified to obtain the best representation of optical spectra for the selected objects. Other adjustable parameters include the stellar radius,R (*), the nebular density,N H, the truncation radius,r c, for the nebular shell, and the chemical composition. Excitationsensitive ratios are usually well-represented as are the actual observed intensities of spectral lines. Forbidden lines arising from 3p 3 configurations, e.g., those of [SII], [ArIV], and [ClIII] offer difficulties. For this sample of nebulae, the mean abundances seem to agree well with those found in an earlier study where the models were used as interpolation devices (Aller, 1978). Our objective is not to use the models to derive abundances explicitly, but rather to use them to find ionization correction factors. Some cautions and limitations of this procedure are described.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00648556
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  • 8
    Electronic Resource
    Electronic Resource
    Theoretical models of planetary nebulae (1980)
    Springer
    Astrophysics and space science 67 (1980), S. 349-366 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Theoretical models are attempted for eight moderate excitation planetary nebulae which have been intensively observed with the image-tube scanner at Lick and in other investigations. The models are uniform density structures, often truncated, with central star energy distributions and chemical compositions so adjusted as to give an optimum fit with the observations. Although a satisfactory representation can be obtained for most of the stronger, usually observed lines, those arising from the 3p 3 configuration, specifically the nebular transitions of [Sii], [Cliii], and [Ariv], often give difficulties. A comparison with results of model predictions with those from simple, traditional procedures generally shows a good agreement, except in those instances where different judgments are made in interpreting emissions of ions of 3p n configurations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00642389
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  • 9
    Electronic Resource
    Electronic Resource
    The chemical composition and structure of 30 Doradus (1980)
    Springer
    Astrophysics and space science 68 (1980), S. 335-346 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Spectrophotometry of many regions within 30 Doradus in the Large Magellanic Cloud provides chemical abundances and densities for this nebular complex. The helium to hydrogen abundance ratio is about one-tenth by number and the heavier elements are underabundant compared to Orion, with nitrogen showing the greatest deficit. The forbidden lines of singly-ionized sulphur show wide density variations across this object. The distribution of the intensities in these sulphur lines suggests that supernova shocks may have played an important role in producing the composite appearance of this giant HII region.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00639703
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  • 10
    Electronic Resource
    Electronic Resource
    A model atmosphere analysis of the binary 112 Herculis (1970)
    Springer
    Astrophysics and space science 9 (1970), S. 461-481 
    Details
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Double-lined spectra have been obtained at 2 Å/mm for the Mn star 112 Herculis AB. The components are shown to be a B6.5V star and A2V star. Hydrogen-line-blanketed models are used to calculate atmospheric abundances. The best models appear to beT e=13500 K, logg=4.0, ξ T =2.5 km/sec for the primary; andT e=10000K, logg=4.2, ξ T =6 km/sec for the secondary. Both stars appear to have the same abundances. Helium, carbon, magnesium, aluminum, silicon, calcium, vanadium, and nickel appear to be considerably underabundant; phosphorus, scandium, titanium, manganese, iron, gallium, and mercury considerably overabundant; and chromium, strontium, and zirconium normal in abundance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00649584
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