White-Light Coronal Structures: Streamers and CMEs

1994 ◽  
Vol 144 ◽  
pp. 82
Author(s):  
E. Hildner
Keyword(s):  
Emission Line ◽  
Electron Density ◽  
White Light ◽  
Coronal Mass Ejections ◽  
X Rays ◽  
Solar Cycles ◽  
Temperature Function ◽  
X Ray ◽  
Eclipse Observations ◽  
Coronal Structures

AbstractOver the last twenty years, orbiting coronagraphs have vastly increased the amount of observational material for the whitelight corona. Spanning almost two solar cycles, and augmented by ground-based K-coronameter, emission-line, and eclipse observations, these data allow us to assess,inter alia: the typical and atypical behavior of the corona; how the corona evolves on time scales from minutes to a decade; and (in some respects) the relation between photospheric, coronal, and interplanetary features. This talk will review recent results on these three topics. A remark or two will attempt to relate the whitelight corona between 1.5 and 6 R⊙to the corona seen at lower altitudes in soft X-rays (e.g., with Yohkoh). The whitelight emission depends only on integrated electron density independent of temperature, whereas the soft X-ray emission depends upon the integral of electron density squared times a temperature function. The properties of coronal mass ejections (CMEs) will be reviewed briefly and their relationships to other solar and interplanetary phenomena will be noted.

scholarly journals Forecasting Solar Energetic Particle (SEP) events with Flare X-ray peak ratios

2018 ◽  
Vol 8 ◽  
pp. A47 ◽  
Author(s):  
Stephen W. Kahler ◽  
Alan. G. Ling
Keyword(s):  
Solar Flare ◽  
Space Weather ◽  
Coronal Mass Ejections ◽  
Energetic Particle ◽  
Solar Energetic Particle ◽  
Western Hemisphere ◽  
X Rays ◽  
X Ray ◽  
Forecasting Methods ◽  
Versus Peak

Solar flare X-ray peak fluxes and fluences in the 0.1–0.8 nm band are often used in models to forecast solar energetic particle (SEP) events. Garcia (2004) [Forecasting methods for occurrence and magnitude of proton storms with solar soft X rays, Space Weather, 2, S02002, 2004] used ratios of the 0.05–0.4 and 0.1–0.8 nm bands of the X-ray instrument on the GOES spacecraft to plot inferred peak flare temperatures versus peak 0.1–0.8 nm fluxes for flares from 1988 to 2002. Flares associated with E > 10 MeV SEP events of >10 proton flux units (pfu) had statistically lower peak temperatures than those without SEP events and therefore offered a possible empirical forecasting tool for SEP events. We review the soft and hard X-ray flare spectral variations as SEP event forecast tools and repeat Garcia’s work for the period 1998–2016, comparing both the peak ratios and the ratios of the preceding 0.05–0.4 nm peak fluxes to the later 0.1–0.8 nm peak fluxes of flares >M3 to the occurrence of associated SEP events. We divide the events into eastern and western hemisphere sources and compare both small (1.2–10 pfu) and large (≥300 pfu) SEP events with those of >10 pfu. In the western hemisphere X-ray peak ratios are statistically lower for >10 pfu SEP events than for non-SEP events and are even lower for the large (>300 pfu) events. The small SEP events, however, are not distinguished from the non-SEP events. We discuss the possible connections between the flare X-ray peak ratios and associated coronal mass ejections that are presumed to be the sources of the SEPs.

Accurate charge densities from powder X-ray diffraction – a new version of the Aarhus vacuum imaging-plate diffractometer

2017 ◽  
Vol 73 (4) ◽  
pp. 521-530 ◽  
Author(s):  
Kasper Tolborg ◽  
Mads R. V. Jørgensen ◽  
Sebastian Christensen ◽  
Hidetaka Kasai ◽  
Jacob Becker ◽  
...  
Keyword(s):  
Electron Density ◽  
High Energy ◽  
Imaging Plate ◽  
High Symmetry ◽  
X Rays ◽  
X Ray Diffraction ◽  
Core Electron ◽  
X Ray ◽  
Peak Broadening ◽  
Structure Factors

In recent years powder X-ray diffraction has proven to be a valuable alternative to single-crystal X-ray diffraction for determining electron-density distributions in high-symmetry inorganic materials, including subtle deformation in the core electron density. This was made possible by performing diffraction measurements in vacuum using high-energy X-rays at a synchrotron-radiation facility. Here we present a new version of our custom-built in-vacuum powder diffractometer with the sample-to-detector distance increased by a factor of four. In practice this is found to give a reduction in instrumental peak broadening by approximately a factor of three and a large improvement in signal-to-background ratio compared to the previous instrument. Structure factors of silicon at room temperature are extracted using a combined multipole–Rietveld procedure and compared withab initiocalculations and the results from the previous diffractometer. Despite some remaining issues regarding peak asymmetry, the new diffractometer yields structure factors of comparable accuracy to the previous diffractometer at low angles and improved accuracy at high angles. The high quality of the structure factors is further assessed by modelling of core electron deformation with results in good agreement with previous investigations.

scholarly journals X-ray line profiles from structured stellar winds

2003 ◽  
Vol 212 ◽  
pp. 214-215
Author(s):  
Lidia M. Oskinova ◽  
Achim Feldmeier ◽  
Wolf-Rainer Hamann
Keyword(s):  
Emission Line ◽  
Thin Shells ◽  
Stellar Winds ◽  
X Rays ◽  
Line Profiles ◽  
X Ray ◽  
Absorbing Material

Absorbing material compressed in a number of thin shells is effectively less opaque for X-rays than smoothly distributed gas. The calculated X-ray emission-line profiles are red-shifted if the emission arises from the starward side of the shells.

scholarly journals Differential Imaging of [Fe X] in IC 443

1988 ◽  
Vol 101 ◽  
pp. 407-410
Author(s):  
Larry Brown ◽  
Bruce E. Woodgate ◽  
Robert Petre
Keyword(s):  
Emission Line ◽  
Electron Density ◽  
Temperature Region ◽  
Supernova Remnant ◽  
Coronal Line ◽  
X Ray ◽  
Imaging Camera ◽  
Differential Imaging ◽  
Einstein Observatory ◽  
Gas Pressures

AbstractThis paper presents images of two areas of the supernova remnant IC443 showing emission from the [Fe X] 6374Å red coronal line taken with an emission line differential imaging camera. The areas are in the vicinity of strong soft X-ray emission as observed with the Einstein Observatory. The [Fe X] emission is patchy on the scale of seconds of arc. For the highest emission regions we find an electron density of approximately 100 cm−3 and gas pressures of 108cm−3K. No correlation is found between the X-ray and [Fe X] knots, and the results support a clumpy, multi-temperature region where the [Fe X] knots are balanced between collapse and evaporation.

Hard X-ray impact on the ionosphere D-layer: new results from VLF measurements

2021 ◽  
Author(s):  
Carine Briand ◽  
Srivani Inturi ◽  
Baptiste Cecconi
Keyword(s):  
Time Delay ◽  
Electron Density ◽  
Recombination Rate ◽  
Peak Time ◽  
X Rays ◽  
X Ray ◽  
Recombination Rate Coefficient ◽  
Maximum Ionization ◽  
Peak Emission

<p>The ionospheric electron density reacts to a change of ionization condition by a time delay Δt. Appleton (1953) demonstrated that this time delay is inversely proportional to the product of the electron density Ne and recombination rate coefficient α. Thus, the evaluation of the time difference between the peak time of VLF emission, which is supposed to represent the instant of maximum ionization, and the ionization source's peak time provides an easy way to estimate α Ne. First used to evaluate the increase of electron density at noon from H α peak emission, this technic was also employed to estimate the recombination rate during solar flares. The GOES Soft X-ray emissions (i.e. in the range 1.5-12keV) are then considered to determine the ionising source peak time.</p><p>Based on VLF measurements obtained from the SUPERSID antenna installed at the Meudon site of the Paris Observatory (France), we computed each flare's time delay from January 2017. We benefit from the events of September 2017, the strongest from the last 10 years. We thus demonstrate the prominent role of Hard X-Rays in ionizing the D-layer of the ionosphere.  </p>

scholarly journals Optical and X-ray observations of stellar flares on an active M dwarf AD Leonis with the Seimei Telescope, SCAT, NICER, and OISTER

2020 ◽  
Vol 72 (4) ◽  
Author(s):  
Kosuke Namekata ◽  
Hiroyuki Maehara ◽  
Ryo Sasaki ◽  
Hiroki Kawai ◽  
Yuta Notsu ◽  
...  
Keyword(s):  
Emission Line ◽  
White Light ◽  
High Energy ◽  
Lower Atmosphere ◽  
Line Profiles ◽  
X Ray ◽  
Energy Beam ◽  
Stellar Flares ◽  
Optical Continuum ◽  
M Dwarf

Abstract We report on multi-wavelength monitoring observations of an M-dwarf flare star AD Leonis with the Seimei Telescope (6150–7930 Å), SCAT (Spectroscopic Chuo-university Astronomical Telescope; 3700–7500 Å), and NICER (Neutron Star Interior Composition Explorer; 0.2–12.0 keV), with the collaboration of the OISTER (Optical and Infrared Synergetic Telescopes for Education and Research) program. Twelve flares are detected in total, including ten Hα, four X-ray, and four optical-continuum flares; one of them is a superflare with a total energy of ∼2.0 × 1033 erg. We found that: (1) during the superflare, the Hα emission line full width at 1/8 maximum dramatically increases to 14 Å from 8 Å in the low-resolution spectra (R ∼ 2000) accompanied by large white-light flares, (2) some weak Hα/X-ray flares are not accompanied by white-light emissions, and (3) the non-flaring emissions show clear rotational modulations in X-ray and Hα intensity in the same phase. To understand these observational features, one-dimensional hydrodynamic flare simulations are performed using the RADYN code. We find the simulated Hα line profiles with hard and high-energy non-thermal electron beams to be consistent with the initial phase line profiles of the superflares, while those with a softer and/or weak-energy beam are consistent with those in decay phases, indicating the changes in the energy fluxes injected to the lower atmosphere. Also, we find that the relation between the optical continuum and Hα intensity is nonlinear, which can be one cause of the non-white-light flares. The flare energy budget exhibits diversity in the observations and models, and more observations of stellar flares are necessary for constraining the occurrence of various emission line phenomena in stellar flares.

Transient electron density maps from femtosecond x-ray powder diffraction

2014 ◽  
Vol 70 (a1) ◽  
pp. C100-C100
Author(s):  
Vincent Juvé ◽  
Flavio Zamponi ◽  
Marcel Holtz ◽  
Michael Woerner ◽  
Thomas Elsaesser
Keyword(s):  
Charge Transfer ◽  
Electron Density ◽  
Powder Diffraction ◽  
Maximum Entropy Method ◽  
Entropy Method ◽  
X Rays ◽  
X Ray ◽  
Density Maps ◽  
Structure Factors ◽  
Diffraction Angle

Ultrashort hard x-ray pulses are sensitive probes of structural dynamics on the picometer length and femtosecond time scales of electronic and atomic motions. Using short hard x-ray pulses as probe in a pump-probe scheme allow to do femtosecond x-ray diffraction experiments [1], which provide transient electron density maps at a femtosecond timescale with a sub-angstrom spatial resolution. In a typical femtosecond x-ray powder diffraction experiment many Debye-Scherrer rings, up to a maximum diffraction angle 2θmax, are recorded for each time delay between the optical pump and the hard x-ray probe. From the diffraction pattern, the change of the diffracted intensity of each rings are monitored. The interference of diffracted x-rays from the many unexcited cells, with known structure factors coming from steady-state measurement, and diffracted x-rays from the few excited cells allows for the detection of the transients structure factors. Problems could arise if the 3D-Fourier transform is directly used because of the abrupt end of the collected information in the reciprocal space (maximum diffraction angle 2θmax). In order to overcome this problem, the Maximum Entropy Method is apply to the data and the transient electron density maps are derived. We apply the femtosecond x-ray powder diffraction technique and the Maximum Entropy Method to study the induced transient polarization by high optical fields on ionic crystals. Such polarizations are connected to a spatial redistribution of electronic charge, which corresponds to a charge transfer between the two ionic compounds [2]. While the charge transfer originates from the anion to the cation in the LiBH and the NaBH4, the LiH exhibits a peculiar behavior: the charge transfer occurs from the cation to the anion. As result from comparison with calculations in the COHSEX framework, this behavior is due to the strong electronic correlations in the LiH [3].

Warpage Structure of 4H-SiC after Implantation and Annealing Processes

2016 ◽  
Vol 858 ◽  
pp. 544-548 ◽  
Author(s):  
Kotaro Ishiji ◽  
Seiji Kawado ◽  
Yasuharu Hirai ◽  
Shinji Nagamachi
Keyword(s):  
Penetration Depth ◽  
White Light ◽  
Curvature Radius ◽  
X Rays ◽  
White Light Interferometry ◽  
Rocking Curve ◽  
X Ray ◽  
Depth Dependence

The warpage structure of 4°-off-axis (0001) 4H-SiC samples after implantation and annealing processes was investigated using white light interferometry (WLI) and X-ray rocking curve (XRC) measurements. The WLI images showed that the surface warpage of the 300 °C-implanted/annealed SiC sample was small and almost the same as that of the un-implanted SiC sample, but the 30 and 150 °C-implanted/annealed SiC samples had a typically saddle-like warpage. The XRCs of the 0008-reflection were measured using monochromatic X-rays with different energies to change the X-ray penetration depth. The subtracted XRCs were reconstructed, and then the depth-dependence of the curvature radius of the 0008-reflection was evaluated. The results indicated that the saddle-like warpage of the 30 and 150 °C-implanted/annealed samples relaxed with increasing depth.

scholarly journals Magnetic electron density in Fe3O4 examined by RXMS at Fe K edge

2014 ◽  
Vol 70 (a1) ◽  
pp. C1555-C1555
Author(s):  
Satoshi Sasaki ◽  
Maki Okube ◽  
Shunichi Takayasu
Keyword(s):  
Crystal Structure ◽  
Fourier Series ◽  
Electron Density ◽  
Magnetic Scattering ◽  
Intensity Difference ◽  
X Rays ◽  
X Ray ◽  
Left Handed ◽  
Difference Fourier ◽  
Magnetic Electron

"It is known that a difference-Fourier synthesis of the Fourier series provides a mean for the location of bonding electrons, by subtracting out the electron density of all atoms in the crystal structure. Here the Fourier technique in X-ray diffraction was applied to observe the magnetic electron density of magnetite Fe3O4. An asymmetrical ratio in the resonant X-ray magnetic scattering (RXMS) provides information on the magnetic moments, which can be estimated from an intensity difference between the right-handed and left-handed polarized X rays. The ratio is proportional to the real part of the product of the spin-contributed structure factor F(hkl) and the complex conjugation of charge-scattered F(hkl). Expanding the equations in difference–Fourier formalization, the spin density can be represented with the observed f""m of RXMS. Synchrotron RXMS experiments were performed at the PF-BL-6C beamline using an AFC-5u four-circle diffractometer. Through a diamond phase retarder the incident X rays were circularly polarized at the Fe K absorption edge, where a wavelength of λ = 1.7439 Å (E = 7.1094 keV) was selected within the pre-edge. A spherical crystal of 0.13 mm in diameter was mounted along the a3 axis with the glass fiber on rare-earth magnet and goniometer head. The intensity data of RXMS were collected for Bragg reflections up to 2θ = 1310. After crystal-structure refinements with scaling of the RXMS data, difference-Fourier syntheses were made in triclinic symmetry with a total of 165 reflections by using the software FRAXY. The syntheses are superior in examining the magnetic effect in the polarization difference and eliminating other effects such as charge scattering, experimental errors and the termination effect. The difference of magnetic electron density between left-handed and right-handed circular polarizations at E was estimated in the Fourier series of partially observed F(hkl). The magnetic electron density on Fourier maps will be discussed in the presentation."

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