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  • 1995-1999  (1)
  • 1975-1979  (9)
  • 1970-1974  (7)
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  • 1
    Electronic Resource
    Electronic Resource
    EUV emission, filament activation and magnetic fields in a slow-rise flare (1975)
    Springer
    Solar physics 41 (1975), S. 397-414 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The evolution of coronal and chromospheric structures is examined together with magnetograms for the 1B flare of January 19, 1972. Soft X-ray and EUV studies are based on the OSO-7 data. The Hα filtergrams and magnetograms came from the Sacramento Peak Observatory. Theoretical force-free magnetic field configurations are compared with structures seen in the soft X-ray, EUV and Hα images. Until the flare, two prominent spots were connected by a continuous dark filament and their overlying coronal structure underwent an expansion at the sunspot separation rate of 0.1 km s−1. On January 19, the flare occurred as new magnetic fields emerged at ∼ 1019 Mx h−1 beneath the filament, which untwisted and erupted as the flare began. The pre-flare coronal emissions remained unchanged during the flare except for the temporary addition of a localized enhancement that started 5 min after flare onset. EUV lines normally emitted in the upper transition region displayed a sudden enhancement coinciding in time and location with a bright Hα point, which is believed to be near the flare ‘trigger’ or onset point. The EUV flash and the initial Hα brightening, both of which occurred near the center of the activated filament, were followed by a second EUV enhancement at the end of the filament. The complete disruption of the filament was accompanied by a third EUV enhancement and a rapid rise in the soft X-ray emission spatially coincident with the disappearing filament. From the change of magnetic field inferred from Hα filtergrams and from force-free field calculations, the energy available for the flare is estimated at approximately 1031 erg. Apparently, changes in the overlying coronal magnetic field were not required to provide the flare energy. Rather, it is suggested that the flare actually started in the twisted filament where it was compressed by emerging fields. Clearly, the flare started below the corona, and it appears that it derived its energy from the magnetic fields in or near the filament.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00154077
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Implications for flare build-up and heating from observations made by OSO-7 (1976)
    Springer
    Solar physics 47 (1976), S. 217-219 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00152258
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Coronal temperatures and temperature gradients from OSO-7 spectroheliograms (1976)
    Springer
    Solar physics 47 (1976), S. 611-626 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Temperatures and temperature gradients for the outer corona are obtained from brightness gradients of EUV lines that were measured with the spectroheliograph on OSO-7. Brightness gradients show considerable deviations from isothermal model calculations that include collisional excitation and photoexcitation. A negative temperature gradient that gives both positive and negative ion abundance gradients appears to be able to account for the discrepancy. For λ284 of Fe xv, perhaps the strongest line from the outer corona, measurements during 1972 appear to be consistent with (i) a temperature near 2.3×106K near the equator at ϱ = 1.3±0.1 solar radii from the solar center; (ii) (ϱ/T) dT/dϱ values near -0.7 that extend from as low as ϱ = 1.2 to about ϱ = 1.8. Temperatures from strong lines of Fe xiv and Fe xvi indicate that variations of about ±0.2×106K exist along lines of sight where emission is appreciable. There appears to be some agreement between these results and temperature measurements from ion abundances in the solar wind and Doppler width of λ5303.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00154770
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    The solar physics Shuttle/Spacelab program and its relationship to studies of the flare build-up (1976)
    Springer
    Solar physics 47 (1976), S. 391-399 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Conclusion The Shuttle/Spacelab program offers an exciting and substantial opportunity for flight of sophisticated instruments for solar research in the 1980's. Problem-oriented missions composed of a number of instruments will be possible as well as flight opportunities for individual instruments developed quickly in response to new knowledge gained from earlier flights. The international scientific community has been asked to participate in defining new facility instruments that are needed. Announcements of Opportunities to participate in the development and use of these instruments will be made by NASA at the appropriate times.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00152278
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    On helium-like 1s2l−1snl′ transitions in solar flare spectra (1974)
    Springer
    Solar physics 36 (1974), S. 121-128 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Expected wavelengths and intensities are computed for 1s2l−1snl′ transitions in helium-like ions of the abundant elements from oxygen to iron, under coronal conditions. Probable observations of some of these lines, in the spectra of solar flares, are discussed and attention is called to a possible reversal of singlet and triplet intensities as compared to laboratory observations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00151552
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    Paper (German National Licenses)
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  • 6
    Electronic Resource
    Electronic Resource
    Ionization equilibrium in soft X-ray-emitting solar flares (1974)
    Springer
    Solar physics 36 (1974), S. 383-401 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Studies of the flare-produced line feature at 1.9 Å due to highly ionized iron show that it is emitted in conditions closely approximating steady-state ionization equilibrium. Calculations of the line flux per unit emission measure from time-dependent and steady-state ionization equilibria are compared with observed values during four flares in particular. Only for electron densities N e ⪞ 1010 cm-3 do the time-dependent equilibrium values give as good an approximation to the observed values as the steady-state equilibrium. This lower limit is compared with values of N e derived from analyses of the temperature decline in each of these events, and with estimates of N e given by other workers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00151209
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    Paper (German National Licenses)
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  • 7
    Electronic Resource
    Electronic Resource
    Observation of possible Fe xvii 2p 53p(1S0)-2p 53s(1 P 1, 3 P 1) transitions in spectra of a solar active region and flare (1975)
    Springer
    Solar physics 43 (1975), S. 111-115 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Expected wavelengths and relative intensities are obtained, from calculations of other workers, for the hitherto unobserved transitions 2p 53p(1 S 0)-2p 53s(1 P 1, 3 P 1) in Fe xvii. A candidate pair of lines at 197.05 Å and 242.09 Å was found in laboratory spectra and appears to be present in the spectra of a solar active region observed by the OSO-7 Goddard spectroheliograph, and in the spectrum of a Skylab-observed solar flare.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00155148
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    Paper (German National Licenses)
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  • 8
    Electronic Resource
    Electronic Resource
    The GSFC EUV and X-ray spectroheliograph on OSO-7 (1974)
    Springer
    Solar physics 35 (1974), S. 241-258 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The Goddard Space Flight Center instrument carried on the pointed section of the OSO-7 satellite is described. This instrument contains: An extreme ultraviolet spectroheliograph using glancing incidence optics of Wolter's Type II to focus the Sun's light on the entrance slit of a concave grating spectrometer; an auxiliary Hα system; two X-ray spectroheliographs using mechanical collimators for spatial resolution and Ross filters to isolate spectral bands of interest, and a flare polarimeter operating in the 15–40 keV X-ray region. These subsystems may be operated in a number of modes which, when combined with the spacecraft modes, give the instrument great flexibility for making solar observations. Representative results from each of the subsystems are presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00151946
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    Paper (German National Licenses)
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  • 9
    Electronic Resource
    Electronic Resource
    Abundance of Fe relative to H at 1.5 solar radii (1975)
    Springer
    Solar physics 42 (1975), S. 487-496 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The abundance of Fe relative to H is obtained by using resonantly scattered intensities of λ 284 of Fe XV that were measured with OSO-7 and resonantly scattered intensities of Lα of H I that were obtained by Gabriel (1971). Because of possible differences in electron densities along lines of sight for these non-simultaneous measurements and in relative calibrations, results are rather uncertain but still indicate that the average Fe abundance relative to H in the corona appears to be at least as large as a recent photospheric abundance. Some limitations in using this method for obtaining abundances are examined for future experiments with simultaneous measurements and well calibrated detectors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00149928
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    Paper (German National Licenses)
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  • 10
    Electronic Resource
    Electronic Resource
    OSO-7 results on coronal emission near 304 Å (1975)
    Springer
    Solar physics 43 (1975), S. 337-350 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The spectral composition and spatial distribution of equatorial coronal emission near 304 Å is examined. Spectral scans indicate that the predominant line is from Si xi. Comparisons of observations with calculations of intensity changes with altitude indicate that collisional excitation is important near the Sun but that photoexcitation becomes dominant beyond about 1.3 R ⊙ from the solar center. Observed and calculated intensities are in approximate agreement for abundances and electron densities that are within the range of observed values.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00152358
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    Paper (German National Licenses)
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