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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
    The cooling of flare produced plasmas in the solar corona (1970)
    Springer
    Solar physics 15 (1970), S. 394-413 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Solar flare X-rays, at energies less than 10 keV, are emitted by hot plasmas located in the corona. Three plasma cooling models are examined in detail. The cooling of the electrons by Coulomb collisions with ions at a lower temperature would require the observed material to occupy very large volumes. Cooling could take place by conduction or by radiation and observations are proposed which would allow the dominant cooling mechanism to be established.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00151847
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  • 3
    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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  • 4
    Electronic Resource
    Electronic Resource
    The soft X-ray polychromator for the Solar Maximum Mission (1980)
    Springer
    Solar physics 65 (1980), S. 53-71 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The 1.4–22.4 Å range of the soft X-ray spectrum includes a multitude of emission lines which are important for the diagnosis of plasmas in the 1.5–50 million degree temperature range. In particular, the hydrogen and helium-like ions of all abundant solar elements with Z 〉 7 have their primary transitions in this region and these are especially useful for solar flare and active region studies. The soft X-ray polychromator (XRP) is a high resolution experiment working in this spectral region. The XRP consists of two instruments with a common control, data handling and power system. The bent crystal spectrometer is designed for high time resolution studies in lines of Fe i-Fe xxvi and Ca xix. The flat crystal scanning spectrometer provides for 7 channel polychromatic mapping of flares and active regions in the resonance lines of O viii, Ne ix, Mg xi, Si xiii, S xv, Ca xix, and Fe xxv with 14″ spatial resolution. In its spectral scanning mode it covers essentially the entire 1.4–22.5 Å region. This paper summarizes the scientific objectives of the XRP experiment and describes the characteristics and capabilities of the two instruments. Sufficient technical information for experiment feasibility studies is included and the resources and procedures planned for the use of the XRP within the context of the Solar Maximum Mission is briefly discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00151384
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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
    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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  • 7
    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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  • 8
    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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  • 9
    Electronic Resource
    Electronic Resource
    Use of Al xii and Mg xi lines as solar plasma diagnostics (1989)
    Springer
    Solar physics 124 (1989), S. 289-302 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We present three sets of observations of n = 1 to n = 2 lines due to helium-like aluminium (Alxii), made during two solar flares (25 August, 1980 and 19 October, 1986), using the X-Ray Polychromator on the SMM satellite. The observed temperature-sensitive line ratio G is shown to be consistent with the close-coupling calculations of Keenan and McCann (1987), although the ratio R, which is both temperature and density-sensitive for lower-Z elements, is not sufficiently well determined from these data to say more than that the observed values of R are not inconsistent with the theoretical calculations. This region of the spectrum also includes the helium-like magnesium (Mgxi) 11 S - 31 P line, and it is shown that the ratio of this line to the Alxii resonance (11 S - 21 P) line is a more sensitive indicator of electron temperature than are the Alxii G and R ratios. We demonstrate that the three ratios may be used together in order to derive values of emission measure, electron temperature and electron density during these flares.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00156271
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  • 10
    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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