X-ray and extreme ultraviolet /1-400 angstrom units/ spectroscopy of the sun, from OSO-III.
Solar X ray and extreme UV spectra during flares, attributing intense emissions to optical transitions
Gates, W. J.↗
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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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Observations of the solar flare soft X-ray spectrum and comparison with centimetric radio bursts.
Solar flare soft X ray and EUV emission spectra data obtained on OSO-3 satellite compared with centimetric radio bursts
Neupert, W. M.↗
Silicon X-ray line emission from solar flares and active regions
New observations of solar flare and active region X-ray spectra obtained with the Columbia University instrument on OSO-8 are presented and discussed. The high sensitivity of the graphite crystal panel has allowed both line and continuum spectra to be served with moderate spectral resolution. Observations with higher spectral resolution have been made with a panel of pentaerythritol crystals. Twenty-nine lines between 1.5 and 7.0 A have been resolved and identified, including several dielectronic recombination satellite lines to Si XIV and Si XIII lines which have been observed for the first time. It has been found that thermal continuum models specified by single values of temperature and emission measure have fitted the data adequately, there being good agreement with the values of these parameters derived from line intensity ratios.
Parkinson, J. H.↗
Nuclear processes and neutrino production in solar flares
The determination of flare neutrino flux is approached from the standpoint of recent observations and theoretical results on the nuclear processes in solar flares. Attention is given to the energy spectra and total numbers of accelerated particles in flares, as well as their resulting production of beta(+)-emitting radionuclei and pions; these should be the primary sources of neutrinos. The observed 0.511 MeV line flux for the June 21, 1980 flare is compared with the expected from the number and spectrum of accelerated particles.
Lingenfelter, R. E.↗
Source energy spectra from demodulation of solar particle data by interplanetary and coronal transport
The data on source energy spectra of solar cosmic rays (SCR), i.e. the data on the spectrum form and on the absolute SCR are of interest for three reasons: (1) the SCR contain the energy comparable to the total energy of electromagnetic flare radiation (less than or equal to 10 to the 32nd power ergs); (2) the source spectrum form indicates a possible acceleration mechanism (or mechanism); and (3) the accelerated particles are efficiently involved in nuclear electromagnetic and plasma processes in the solar atmosphere. Therefore, the data on SCR source spectra are necessary for a theoretical description of the processes mentioned and for the formulation of the consistent flare model. Below it is attempted to sound solar particle sources by means of SCR energy spectrum obtained near the Sun, at the level of the roots of the interplanetary field lines in the upper solar corona. Data from approx. 60 solar proton events (SPE) between 1956-1981. These data were obtained mainly by the interplanetary demodulation of observed fluxes near the Earth. Further, a model of coronal azimuthal transport is used to demodulate those spectra, and to obtain the source energy spectra.
Perez-Peraza, J.↗
New ionization fractions for the lithium- and helium-like ionization stages of calcium and iron
A reinterpretation of the high resolution X-ray spectra of Ca XIX and Fe XXV, observed during a solar flare on March 25, 1979, is presented. New ionization fractions for Ca XVIII, Ca XIX, Fe XXIV, and Fe XXV are used, and it is shown that the new calculations substantially change the interpretation of the spectra. It is implied that the flare plasma was ionizing during the early phases of the flare, and recombining during the decay phase.
Doyle, J. G.↗
Relativistic electron events in interplanetary space
Review of relativistic electron events observed in interplanetary space. The different types of event are identified and illustrated. The relationships between solar X-ray and radio emissions and relativistic electrons are examined, and the relevance of the observations to solar flare acceleration models is discussed. A statistical analysis of electron spectra, the electron/proton ratio and propagation from the flare site to the earth is presented. A model is outlined which can account for the release of electrons from the sun in a manner consistent with observations of energetic solar particles and electromagnetic solar radiation.
Simnett, G. M.↗
Charge states of low energy ions from the sun
Measurements of ionization states and energy spectra of carbon, oxygen, and iron accelerated in ten solar flare particle events are reported, for energies between 15 keV per nucleon and 600 keV per nucleon. The ionization states were remarkably constant from flare to flare, despite great variations in other event parameters. The mean ionization state for carbon was 5.7, for oxygen 6.2, and for iron 11.7, values which are similar to the respective ionization states in the solar wind. The time profile of the He/C+N+O ratio was examined, and it was found that the ratio was small early in the event, and increased with time. The energy spectra of the medium ions showed a flattening below 100 keV per nucleon, which was highly correlated with event size as measured by the event averaged flux of 130 to 220 keV protons.
Sciambi, R. K.↗
Neutrons and Gamma Rays from Solar Flares
The theory of neutron and gamma-ray production in flares is reviewed and comparisons of the calculations with data are made. The principal conclusions pertain to the accelerated proton and electron numbers and spectra in flares and to the interaction site of these particles in the solar atmosphere. For the June 21, 1980 flare, from which high-energy neutrons and high-energy ( MeV) photons were seen, the electron-to-proton ratio is energy dependent and much smaller than unity at energies greater than 1 MeV. The interaction site of these particles appears to be the solar chromosphere.
Ramaty, R.↗
H-alpha flare spectra
More than 1000 H-alpha flare profiles from 24 solar flares of Class 1 or brighter recorded with the multislit spectrograph of the Lockheed Solar Observatory are examined. It is found that the profiles can be classified in terms of whether or not they show central self-reversals, whether or not they have extended wings, and whether or not they are asymmetric. The profile groupings are not correlated with the size (class) of the flares, nor do they seem to be correlated with the type of chromospheric flare structure from which they are emitted. Although different flare points within the same overall event may show profiles of different types, any given element (bright patch) can usually be described in terms of a single combination of the profile descriptors.
Schoolman, S. A.↗
Solar observations and atomic data for the 3s2 1s0-3s3p 3P1 transition in S v
High resolution solar observations of the S v intersystem line at 1199.18 A are available from Skylab. This line is potentially useful as a density diagnostic for high density plasmas expected in solar flares. S v lines are also prominent in solar spectra at wavelengths below 1000 A. Collision strengths and radiative decay rates are calculated for levels of the configurations 3 s2, 3s3p, 3p2, and 3s3d. Level populations for the five lowest energy levels have been calculated as a function of electron density. These calculations are carried out assuming the temperature at which S v is most abundant in solar plasmas. The calculated population of the 3s3p 3P1 level reaches a pseudo-Boltzmann equilibrium at a density which is about five times higher than is derived from solar spectra and previous density determinations. It is believed that the discrepancy is due to a significant contribution from resonances to the 3s2-3s3p 3P excitation rate coefficient. It is suggested that the contribution of the resonances to the S v excitation rate coefficient can be estimated from a comparison of the experimental results and the theoretical calculations.
Feldman, U.↗
A comparison of theoretical and solar-flare intensity ratios for the Fe XIX X-ray lines
Atomic data including energy levels, gf-values, and wavelengths are given for the Fe XIX transitions that give rise to lines in solar-flare and active-region X-ray spectra. Collision strengths and theoretical intensity ratios are presented for lines which occur in the 13.2-14.3-A range. Observed spectra are found to be consistent with those derived from the present Fe XIX atomic data. For the case of spectra in which the Fe XIX lines are very strong, such as those at the maxima of hot flares, two observed line features due to Fe XIX are shown to have larger intensities than calculated. The calculated Fe XIX and Ne IX line spectra are used to determine electron densities from Ne IX line ratios.
Bhatia, A. K.↗
Estimates of HZE particle contributions to SPE radiation exposures on interplanetary missions
Estimates of radiation doses resulting from possible HZE (high energy heavy ion) components of Solar Particle Events (SPEs) are presented for crews of manned interplanetary missions. The calculations assume a model spectrum obtained by folding measured solar flare HZE particle abundances with the measured energy spectra of SPE alpha particles. These hypothetical spectra are then transported through aluminum spacecraft shielding. The results, presented as estimates of absorbed dose and dose equivalent, indicate that HZE components by themselves are not a major concern for crew protection but should be included in any overall risk assessment. The predictions are found to be sensitive to the assumed spectral hardness parameters.
Townsend, L. W.↗
ASCA Observations of the Barnard 209 Dark Cloud and an Intense X-Ray Flare on V773 Tauri
ASCA (Advanced Satellite for Cosmology and Astrophysics) detected an intense X-ray flare on the weak-lined T Tauri star V773 Tau (=HD 283447) during a 30 ks observation of the Barnard 209 dark cloud in 1995 September. This star is a spectroscopic binary and shows signs of strong magnetic surface activity including a spot-modulated optical light curve. The flare was seen only during its decay phase but is still one of the strongest ever recorded from a T Tauri star with a peak luminosity L(sub x) = 10(exp 32.4) ergs/s (0.5-10 keV), a maximum temperature of at least 42 million K, and energy release of greater than 10(exp 37) ergs. A shorter ASCA observation taken five months later showed V773 Tau in a quiescent state (L(sub x)= 10(exp 31.0) ergs/s) and detected variable emission from the infrared binary IRAS 04113+2758. The differential emission measure (DEM) distribution during the V773 Tau flare shows a bimodal temperature structure that is almost totally dominated by hot plasma at an average temperature of approx. 37 million K. Using information from time-resolved spectra, we examine the flare decay in terms of solar flare models (cooling loops and two-ribbon flares) and also consider possible nonsolar behavior (interbinary flares, star-disk flares, and rotational X-ray modulation). Solar models are unable to reproduce the unusual convex-shaped X-ray light curve, which decays slowly over a timespan of at least 1 day. However, the light curve decay is accurately modeled as a sinusoid with an inferred X-ray period of 2.97 days, which is nearly identical to the optical rotation period(s) of the two K-type components. This provides tantalizing evidence that the flaring region was undergoing rotational occultation, but periodic X-ray variability is not yet proven since our ASCA observation spans only one-third of a rotation cycle.
Skinner, Stephen L.↗
Particle Acceleration during Magnetic Reconnection in Solar Flares and Its Parameter Dependence [Slide]
Time evolution of the electron and proton energy spectra in our 3D reconnection simulation. For the first time, the spectra form power laws with stable slopes over time for both species.
79 ASTRONOMY AND ASTROPHYSICS↗
On the nonthermal excitation and polarization of X-ray lines during solar flares
The energy distributions of nonthermal electrons are derived from hard X-ray spectra taken during the impulsive phase of two 2B flares in February 1969. They are used to calculate the fluxes of nonthermally excited X-ray lines of hydrogen-like and helium-like ions. These fluxes are compared to the total line fluxes observed at the same time with crystal spectrometers. The nonthermal excitation is found to give only small contributions to the total line intensities. This implies that the impact polarization which is to be expected for anisotropic velocity distributions of the energetic electrons, will be low. Nevertheless it should be feasible to detect line polarization during the impulsive phase of strong X-ray flares.
Haug, E.↗
Workshop on orbiting solar observatories
OSO satellites observations, studying X ray flare phases, temperatures and spectra
Brandt, J. C.↗
Flat microwave spectra seen at X-class flares
We report peculiar spectral activity of four large microwave bursts as obtained from the Solar Arrays at the Owens Valey Radio Observatory during observations of X-class flares on 24 May 1990 and 7, 8, 22 March 1991. Main observational points that we newly uncovered are: (1) flat flux spectra over 1-18 GHz in large amounts of flux ranging from 10(exp 2) to 10(exp 4) s.f.u. at the maximum phase, (2) a common evolutionary pattern in which the spectral region of dominant flux shifts from high frequencies at the initial rise to low frequencies at the decaying phase, and (3) unusual time profiles that are impulsive at high frequencies but more extended at lower frequencies. We carry out the model calculations of microwave spectra under assumptions of gyrosynchrotron mechanism and a dipole field configuration to reproduce the observational characteristics. Our results are summarized as follows. First, a flat microwave spectrum reaching up to 10(exp 2) - 10(exp 4) s.f.u. may occur in a case where a magnetic loop is extended to an angular size of approximately (0.7-7.0) x 10(exp -7) sterad and contains a huge number (N(E greater than 10 keV) approx. 10(exp 36) - 10(exp 38)) of nonthermal electrons with power-law index approx. 3-3.5 over the entire volume. Second, the observed spectral activity could adequately be accounted for by the shrinking of the region of nonthermal electrons to the loop top and by the softening of the power-law spectrum of electrons in a time scale ranging 3-45 min depending on the event. Third, the extended microwave activity at lower frequencies is probably due to electrons trapped in the loop top where magnetic fields are low. Finally, we clarify the physical distinction between these large, extended microwave bursts and the gradual/post-microwave bursts often seen in weak events, both of which are characterized by long-period activity and broadband spectra.
Lee, Jeongwoo W.↗