F. P. Keenan
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View article: Identification of new gold lines in the 350–1000 nm spectral region using laser produced plasmas
Identification of new gold lines in the 350–1000 nm spectral region using laser produced plasmas Open
We present results from a pilot study, using a laser-produced plasma, to identify new lines in the 350–1000 nm spectral region for the r-process element gold (Au), of relevance to studies of neutron star mergers. This was achieved via opti…
View article: Generation of photoionized plasmas in the laboratory of relevance to accretion-powered x-ray sources using keV line radiation
Generation of photoionized plasmas in the laboratory of relevance to accretion-powered x-ray sources using keV line radiation Open
We describe laboratory experiments to generate x-ray photoionized plasmas of relevance to accretion-powered x-ray sources such as neutron star binaries and quasars, with significant improvements over previous work. A key quantity is refere…
View article: Generation of photoionized plasmas in the laboratory of relevance to accretion-powered x-ray sources using keV line radiation
Generation of photoionized plasmas in the laboratory of relevance to accretion-powered x-ray sources using keV line radiation Open
We describe laboratory experiments to generate X-ray photoionized plasmas of relevance to accretion-powered X-ray sources such as neutron star binaries and quasars, with significant improvements over previous work. A key quantity is refere…
View article: Power-law Distribution of Solar Cycle–modulated Coronal Jets
Power-law Distribution of Solar Cycle–modulated Coronal Jets Open
Power-law distributions have been studied as a significant characteristic of nonlinear dissipative systems. Since discovering the power-law distribution of solar flares that was later extended to nanoflares and stellar flares, it has been …
View article: Power-law Distribution of Solar-Cycle Modulated Coronal Jets
Power-law Distribution of Solar-Cycle Modulated Coronal Jets Open
Power-law distributions have been studied as a significant characteristic of non-linear dissipative systems. Since discovering the power-law distribution of solar flares that was later extended to nano-flares and stellar flares, it has bee…
View article: L-Shell X-Ray Conversion Yields for Laser-Irradiated Tin and Silver Foils
L-Shell X-Ray Conversion Yields for Laser-Irradiated Tin and Silver Foils Open
We have employed the VULCAN laser facility to generate a laser plasma X-ray source for use in photoionization experiments. A nanosecond laser pulse with an intensity of order 10 15 Wcm −2 was used to irradiate thin Ag or Sn foil targets co…
View article: High-frequency Waves in Chromospheric Spicules
High-frequency Waves in Chromospheric Spicules Open
Using high-cadence observations from the Hydrogen-alpha Rapid Dynamics camera imaging system on the Dunn Solar Telescope, we present an investigation of the statistical properties of transverse oscillations in spicules captured above the s…
View article: Improved Fe ii Emission-line Models for AGNs Using New Atomic Data Sets
Improved Fe ii Emission-line Models for AGNs Using New Atomic Data Sets Open
Understanding the Fe II emission from active galactic nuclei (AGNs) has been a grand challenge for many decades. The rewards from understanding the AGN spectra would be immense, involving both quasar classification schemes such as “Eigenve…
View article: Electron-impact Excitation of Fe i
Electron-impact Excitation of Fe i Open
The Fe i spectra emitted by astrophysical sources contain information on plasma parameters such as chemical abundances and magnetic fields. However, to determine these parameters requires detailed plasma modeling, which in turn needs accur…
View article: Electron-impact excitation of Mn V
Electron-impact excitation of Mn V Open
The file omegau contains (unformatted) collision strengths for electron-impact excitations among 200 fine-struture levels in Mn V, evaluated at 92,601 incident electron energies between 0 and 9 rydbergs. The code xtrct.f extracts collision…
View article: Electron-impact excitation of Mn V
Electron-impact excitation of Mn V Open
The file omegau contains (unformatted) collision strengths for electron-impact excitations among 200 fine-struture levels in Mn V, evaluated at 92,601 incident electron energies between 0 and 9 rydbergs. The code xtrct.f extracts collision…
View article: An investigation of the L-shell x-ray conversion efficiency for laser-irradiated tin foils
An investigation of the L-shell x-ray conversion efficiency for laser-irradiated tin foils Open
We have used the Shenguang II laser in third harmonic (351 nm) to investigate the emission of L-shell radiation in the 3.3–4.4 keV range generated using thin foils of Sn coated onto a parylene substrate with irradiation of order 1015 W cm−…
View article: Towards the Provision of Accurate Atomic Data for Neutral Iron
Towards the Provision of Accurate Atomic Data for Neutral Iron Open
The rich emission and absorption line spectra of Fe I may be used to extract crucial information on astrophysical plasmas, such as stellar metallicities. There is currently a lack, in quality and quantity, of accurate level-resolved effect…
View article: Benchmarking Current Capabilities for the Generation of Excitation and Photoionisation Atomic Data
Benchmarking Current Capabilities for the Generation of Excitation and Photoionisation Atomic Data Open
The spectra currently emerging from modern ground- and space-based astronomical instruments are of exceptionally high quality and resolution. To meaningfully analyse these spectra, researchers utilise complex modelling codes to replicate t…
View article: Towards the Provision of Accurate Atomic Data for Neutral Iron
Towards the Provision of Accurate Atomic Data for Neutral Iron Open
The rich emission and absorption line spectra of Fe I may be used to extract crucial information on astrophysical plasmas, such as stellar metallicities. There is currently a lack, in quality and quantity, of accurate level-resolved effect…
View article: Benchmarking Current Capabilities for the Generation of Excitation and Photoionisation Atomic Data
Benchmarking Current Capabilities for the Generation of Excitation and Photoionisation Atomic Data Open
The spectra currently emerging from modern ground- and space-based astronomical instruments are of exceptionally high quality and resolution. To meaningfully analyse these spectra researchers utilise complex modelling codes to replicate th…
View article: Production of photoionized plasmas in the laboratory with x-ray line radiation
Production of photoionized plasmas in the laboratory with x-ray line radiation Open
In this paper we report the experimental implementation of a theoretically proposed technique for creating a photoionized plasma in the laboratory using x-ray line radiation. Using a Sn laser plasma to irradiate an Ar gas target, the photo…
View article: Photospheric Observations of Surface and Body Modes in Solar Magnetic Pores
Photospheric Observations of Surface and Body Modes in Solar Magnetic Pores Open
Over the past number of years, great strides have been made in identifying the various low-order magnetohydrodynamic wave modes observable in a number of magnetic structures found within the solar atmosphere. However, one aspect of these m…
View article: A Si iv/O iv Electron Density Diagnostic for the Analysis of IRIS Solar Spectra
A Si iv/O iv Electron Density Diagnostic for the Analysis of IRIS Solar Spectra Open
Solar spectra of ultraviolet bursts and flare ribbons from the Interface Region Imaging Spectrograph ( IRIS ) have suggested high electron densities of cm −3 at transition region temperatures of 0.1 MK, based on large intensity rati…
View article: X-ray line coincidence photopumping in a solar flare
X-ray line coincidence photopumping in a solar flare Open
Line coincidence photopumping is a process where the electrons of an atomic or molecular species are radiatively excited through the absorption of line emission from another species at a coincident wavelength. There are many instances of l…
View article: The formation of small-scale umbral brightenings in sunspot atmospheres
The formation of small-scale umbral brightenings in sunspot atmospheres Open
\n Context. Sunspot atmospheres have been shown to be highly inhomogeneous hosting both quasi-stable and transient features, such as small-scale umbral brightenings (previously named “umbral micro-jets”) and dark fibril-like events.\n Aims…
View article: Spectroscopic Inversions of the Ca ii 8542 Å Line in a C-class Solar Flare
Spectroscopic Inversions of the Ca ii 8542 Å Line in a C-class Solar Flare Open
We study the C8.4 class solar flare SOL2016-05-14T11:34 UT using\nhigh-resolution spectral imaging in the Ca ii 8542 {\\AA} line obtained with the\nCRISP imaging spectropolarimeter on the Swedish 1-m Solar Telescope.\nSpectroscopic inversi…
View article: Radiative Rates and Electron Impact Excitation Rates for Transitions in He II
Radiative Rates and Electron Impact Excitation Rates for Transitions in He II Open
We report calculations of energy levels, radiative rates, collision strengths and effective collision strengths for transitions among the lowest 25 levels of the n ≤ 5 configurations of He II. The general-purpose relativistic atomic struct…
View article: An assessment of Fe xx–Fe xxii emission lines in SDO/EVE data as diagnostics for high-density solar flare plasmas using EUVE stellar observations
An assessment of Fe xx–Fe xxii emission lines in SDO/EVE data as diagnostics for high-density solar flare plasmas using EUVE stellar observations Open
The Extreme Ultraviolet Variability Experiment (EVE) on the Solar Dynamics Observatory obtains extreme-ultraviolet (EUV) spectra of the full-disc Sun at a spectral resolution of ∼1 Å and cadence of 10 s. Such a spectral resolution would no…
View article: Electron impact excitation of N iv: calculations with the darc code and a comparison with ICFT results
Electron impact excitation of N iv: calculations with the darc code and a comparison with ICFT results Open
There have been discussions in the recent literature regarding the accuracy of the available electron impact excitation rates (equivalently effective collision strengths ϒ) for transitions in Be-like ions. In the present paper we demo…