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  • 1
    Electronic Resource
    Electronic Resource
    Inner-shell x-ray line spectra of highly ionized titanium, chromium, iron, and nickel and their application to laboratory plasmas (1986)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 60 (1986), S. 1960-1973 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The intensities of x-ray lines due to inner-shell 1s-2p transitions in O i-, N i-, and C i-like ions of Ti xv–xvii, Cr xvii-xix, Fe xix-xxi, and Ni xxi-xxiii seen in tokamak plasmas are calculated. The lines are assumed to be formed by dielectronic recombination and inner-shell excitation. The present calculations are an extension of previous work for iron alone. The dielectronic contribution for iron was found to be more important, and this is true for the ions of titanium, chromium, and nickel considered here. The dielectronic rates were calculated using a suite of computer programs developed by one of us. The inner-shell contribution was estimated by van Regemorter's formula. The considered ion stages have two or more fine-structure levels in the ground configuration, which gives rise to a density dependence of both dielectronic and collision excitation mechanisms at densities between 1011 and 1016 cm−3, a range suitable for tokamak plasmas. A means for determining the density of high-temperature plasmas is presented for when no other density diagnostics are available. Finally, the present calculations were applied to the problem of radial ion diffusion in tokamaks. Spectra were calculated by integrating along various lines of sight to simulate what might be observed by an actual spectrometer viewing a tokamak plasma. The assumed temperature and density profiles and two diffusion models were taken from a recent calculation. A method for determining the diffusion coefficient from tokamak observations is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.337197
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  • 2
    Electronic Resource
    Electronic Resource
    Distance to Cygnus X-1 (1974)
    [s.l.] : Nature Publishing Group
    Nature 251 (1974), S. 589-590 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Accurate estimates of the distance to HDE226868 have recently been claimed by Margon et al.3 and Bregman et al.4 who give 2.5 kpc. Such a large distance favours the black hole model. Both works used the reddening produced by interstellar dust as a distance indicator. A consistent distance?reddening ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/251589a0
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  • 3
    Electronic Resource
    Electronic Resource
    Solar X-ray bursts at energies less than 10 keV observed with OSO-4 (1970)
    Springer
    Solar physics 11 (1970), S. 117-144 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Using data from a proportional counter spectrometer, sensitive in the wavelength range 1–20 Å, on OSO-4, X-ray bursts in the energy band 3.0 to 4.5 keV have been studied. 150 events have been identified between October 27, 1967 and May 8, 1968, mostly of an impulsive nature. Some gradual rise and fall bursts occur, but there is a selection bias against such long-enduring events. A study of the profiles of these events reveals no basis for identifying different types of impulsive event. Single frequency radio bursts and Hα flares of class 〉 1F are almost always accompanied by X-ray enhancements. For the sample of X-ray events, only 25% are correlated with radio bursts and 46% with flares. Only 11% of the sample events are associated with type III radio bursts. Microwave burst peaks occur an average of two minutes earlier than the X-ray burst peak, but the first observation of X-ray activity is usually before the start of the corresponding microwave burst. Impulsive bursts, although differing widely in fall time, are due to the heating of a volume of plasma from a temperature of 10.0 to 30.0 × 106 K. Differences infall time probably indicate different electron densities in the source. Observation of an iron line at 1.9 Å suggests that a non-thermal mechanism may be operating during some of these events since the temperatures are too low to permit thermal excitation of the 1s 2-1s 2p transition in Fe+24. It is also possible that, in spite of the low temperature, most of the iron ions have been stripped to the Fe+24 stage. Collisional excitation and dielectronic recombination processes would then be able to provide the observed flux in the resonance line of Fe+24. A gradual rise and fall event and event ‘precursors’ have also been studied.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00156556
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  • 4
    Electronic Resource
    Electronic Resource
    The Bragg Crystal Spectrometer for SOLAR-A (1991)
    Springer
    Solar physics 136 (1991), S. 89-104 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The Bragg Crystal Spectrometer (BCS) is one of the instruments which makes up the scientific payload of the SOLAR-A mission. The spectrometer employs four bent germanium crystals, views the whole Sun and observes the resonance line complexes of H-like Fexxvi and He-like Fexxv, Caxix, and Sxv in four narrow wavelength ranges with a resolving power (λ/Δλ) of between 3000 and 6000. The spectrometer has approaching ten times better sensitivity than that of previous instruments thus permitting a time resolution of better than 1 s to be achieved. The principal aim is the measurement of the properties of the 10 to 50 million K plasma created in solar flares with special emphasis on the heating and dynamics of the plasma during the impulsive phase. This paper summarizes the scientific objectives of the BCS and describes the design, characteristics, and performance of the spectrometers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00151696
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  • 5
    Electronic Resource
    Electronic Resource
    Fe XVIII EMISSION LINES IN SOLAR X-RAY SPECTRA (1997)
    Springer
    Solar physics 171 (1997), S. 93-102 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have calculated intensity ratios for emission lines of Fexviii in the 13–94 Å wavelength range at electron temperatures characteristic of the solar corona, T e = 2–10 x 106 K. Our model ion includes data for transitions among the 2s 22p 5 , 2s2p 6, 2s 22p 43l, and 2s2p 53l (l = s, p, and d) states. Test calculations which omit the 2s2p 53l levels show that cascades from these are important. We compare our results with observed ratios determined from four solar X-ray instruments, a rocket-borne spectrograph, and spectrometers on the P78–1, OV1–17 and Solar Maximum Mission (SMM) satellites. In addition, we have generated synthetic spectra which we compare directly with flare observations from SMM. Agreement between theory and observation is generally quite good, with differences that are mostly less than 30%, providing limited support for the accuracy of the atomic physics data used in our calculations. However, large discrepancies are found for ratios involving the 2s 22p 5 2P3/2- 2s2p 6 2S line at 93.84 Å, which currently remain unexplained. Our analysis indicates that the FeXVIII feature at 15.83 Å is the 2s 22p 5 2P3/2 - 2s 22p 4(3P)3s 4P3/2 transition, rather than 2s 22p 5 2P3/2 - 2s 22p 4(3P)3s 2P3/2, as suggested by some authors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004934523755
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  • 6
    Electronic Resource
    Electronic Resource
    Comments on the Zirin-Frazier controversy (1973)
    Springer
    Solar physics 29 (1973), S. 383-384 
    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/BF00150815
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  • 7
    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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  • 8
    Electronic Resource
    Electronic Resource
    A model for X-ray emission from loop prominences (1977)
    Springer
    Solar physics 53 (1977), S. 41-58 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A study is made of X-ray line emission observed during the developing stages of a set of post-flare loop prominences. The time behaviour of the line emission can be described by a model consisting of two flux tubes containing plasma heated impulsively at the flash phase; the plasma cools by radiation and by conduction to the chromosphere. These ideas are extended to the possible formation of Hα prominences from low-lying hot loops.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02260208
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  • 9
    Electronic Resource
    Electronic Resource
    A comment on solar flare iron line emission at 1.9 Å (1971)
    Springer
    Solar physics 16 (1971), S. 469-471 
    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/BF00162489
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  • 10
    Electronic Resource
    Electronic Resource
    Kα line emission during solar X-ray bursts (1973)
    Springer
    Solar physics 32 (1973), S. 209-225 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Kα X-ray line emission from S, Ar, Ca and Fe is calculated for conditions likely to exist in solar flares. We consider both the non-thermal and thermal phases of flares as indicated by X-ray observations. Impulsive non-thermal events seen at the onset of a flare at photon energies 〉 20 keV generally give rise to small Kα line fluxes (〈250 photons cm-2 s-1) on the basis of data presented by Kane and Anderson. The amount of S Kα radiation in particular depends sensitively on the lower-energy bound of the non-thermal electron distribution giving rise to the impulsive burst, offering a possible means of determining this. Thermal Kα emission is significant for only Fe ions. For S, Ar and Ca, the temperatures required for a sizeable number of electrons with energies greater than the K-ionization potential will also strip these elements to ionization stages too high for Kα transitions to be possible. Comparison of thermal Kα emission from iron during an intense solar flare leads to a very high emission measure on the basis of these calculations, but such a value seems to be compatible with an analysis of the 1–3 Å continuum during the same event.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00152737
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