Results for "F. P. Keenan"

total 166799took 0.18s
Energy levels, radiative rates and lifetimes for transitions in Br-like ions with 38 $\le$ Z $\le$ 42Sep 26 2014Energy levels and radiative rates for transitions in five Br-like ions (Sr IV, Y V, Zr VI, Nb VII and Mo VIII) are calculated with the general-purpose relativistic atomic structure package ({\sc grasp}). Extensive configuration interaction has been included ... More
Radiative rates for E1, E2, M1, and M2 transitions in the Br-like ions Sr IV, Y V, Zr VI, Nb VII, and Mo VIIIApr 01 2015Energies and lifetimes are reported for the lowest 375 levels of five Br-like ions, namely Sr~IV, Y~V, Zr~VI, Nb~VII, and Mo~VIII, mostly belonging to the 4s$^2$4p$^5$, 4s$^2$4p$^4$4$\ell$, 4s4p$^6$, 4s$^2$4p$^4$5$\ell$, 4s$^2$4p$^3$4d$^2$, 4s4p$^5$4$\ell$, ... More
Radiative rates for E1, E2, M1, and M2 transitions in S-like to F-like tungsten ions (W LIX to W LXVI)Feb 12 2016Calculations of energy levels, radiative rates and lifetimes are reported for eight ions of tungsten, i.e. S-like (W LIX) to F-like (W LXVI). A large number of levels has been considered for each ion and extensive configuration interaction has been included ... More
Electron impact excitation of Be-like ions: a comparison of DARC and ICFT resultsJan 05 2015Emission lines of Be-like ions are frequently observed in astrophysical plasmas, and many are useful for density and temperature diagnostics. However, accurate atomic data for energy levels, radiative rates (A-values) and effective electron excitation ... More
Radiative rates for E1, E2, M1, and M2 transitions in Br-like ions with 43 $\le$ Z $\le$ 50Jul 15 2015Energies and lifetimes are reported for the eight Br-like ions with 43 $\le$ Z $\le$ 50, namely Tc ~IX, Ru~X, Rh~XI, Pd~XII, Ag~XIII, Cd~XIV, In~XV, and Sn~XVI. Results are listed for the lowest 375 levels, which mostly belong to the 4s$^2$4p$^5$, 4s$^2$4p$^4$4$\ell$, ... More
Energy levels, radiative rates and electron impact excitation rates for transitions in C IIIMar 26 2015We report energy levels, radiative rates (A-values) and lifetimes for the astrophysically-important Be-like ion C III. For the calculations, 166 levels belonging to the $n \le$ 5 configurations are considered and the {\sc grasp} (General-purpose Relativistic ... More
Energy levels, radiative rates and electron impact excitation rates for transitions in Al XNov 21 2013Energy levels, radiative rates and lifetimes are calculated among the lowest 98 levels of the n <= 4 configurations of Be-like Al X. The GRASP (General-purpose Relativistic Atomic Structure Package) is adopted and data are provided for all E1, E2, M1 ... More
Energy levels, radiative rates and electron impact excitation rates for transitions in He-like Kr XXXVJul 27 2012We report calculations of energy levels, radiative rates and electron impact excitation cross sections and rates for transitions in He-like Kr XXXV. The GRASP (general-purpose relativistic atomic structure package) is adopted for calculating energy levels ... More
Energy levels, radiative rates and electron impact excitation rates for transitions in Fe XIVSep 15 2014Energies and lifetimes are reported for the lowest 136 levels of Fe XIV, belonging to the (1s$^2$2s$^2$2p$^6$) 3s$^2$3p, 3s3p$^2$, 3s$^2$3d, 3p$^3$, 3s3p3d, 3p$^2$3d, 3s3d$^2$, 3p3d$^2$ and 3s$^24\ell$ configurations. Additionally, radiative rates, oscillator ... More
Comment on "Multiconfiguration Dirac-Fock energy levels and radiative rates for Br-like tungsten" by S. Aggarwal, A.K.S. Jha, and M. Mohan [Can . J. Phys. 91 (2013) 394]Oct 24 2013We report calculations of energy levels and oscillator strengths for transitions in W XL, undertaken with the general-purpose relativistic atomic structure package ({\sc grasp}) and flexible atomic code ({\sc fac}). Comparisons are made with existing ... More
Radiative rates for E1, E2, M1, and M2 transitions in F-like ions with 37 $\le$ Z $\le$ 53Dec 01 2015Calculations of energy levels, radiative rates and lifetimes are reported for 17 F-like ions with 37 $\le$ Z $\le$ 53. For brevity, results are only presented among the lowest 113 levels of the 2s$^2$2p$^5$, 2s2p$^6$, 2s$^2$2p$^4$3$\ell$, 2s2p$^5$3$\ell$, ... More
Radiative rates for E1, E2, M1, and M2 transitions among the 3s$^2$3p$^5$, 3s3p$^6$, and 3s$^2$3p$^4$3d configurations of Cl-like W LVIIIJan 16 2014We report calculations of energy levels, radiative decay rates, and lifetimes for transitions among the 3s$^2$3p$^5$, 3s3p$^6$, and 3s$^2$3p$^4$3d configurations of Cl-like W LVIII. The general-purpose relativistic atomic structure package (GRASP) has ... More
Energy levels, radiative rates, and electron impact excitation rates for transitions in Li-like ions with 12 <= Z <= 20Jul 05 2012We report calculations of energy levels, radiative rates, and electron impact excitation rates for transitions in Li-like ions with 12 <= Z <= 20. The GRASP (general-purpose relativistic atomic structure package) is adopted for calculating energy levels ... More
Mechanisms for MHD Poynting flux generation in simulations of solar photospheric magneto-convectionMay 31 2012We investigate the generation mechanisms of MHD Poynting flux in the magnetised solar photosphere. Using radiative MHD modelling of the solar photosphere with initial magnetic configurations that differ in their field strength and geometry, we show the ... More
Energy levels, radiative rates and electron impact excitation rates for transitions in Be-like Cl XIV, K XVI and Ge XXIXSep 12 2014Results for energy levels, radiative rates and electron impact excitation (effective) collision strengths for transitions in Be-like Cl XIV, K XVI and Ge XXIX are reported. For the calculations of energy levels and radiative rates the General-purpose ... More
Energy levels, radiative rates, and lifetimes for transitions in W LVIIIJun 11 2014Energy levels and radiative rates are reported for transitions in Cl-like W LVIII. Configuration interaction (CI) has been included among 44 configurations (generating 4978 levels) over a wide energy range up to 363 Ryd, and the general-purpose relativistic ... More
Electron impact excitation rates for transitions in Mg VSep 27 2016Energy levels, radiative rates (A-values) and lifetimes, calculated with the GRASP code, are reported for an astrophysically important O-like ion Mg~V. Results are presented for transitions among the lowest 86 levels belonging to the 2s$^2$2p$^4$, 2s2p$^5$, ... More
Energy levels and radiative rates for transitions in Fe V, Co VI and Ni VIIMay 26 2016Energy levels, Land\'{e} $g$-factors and radiative lifetimes are reported for the lowest 182 levels of the 3d$^4$, 3d$^3$4s and 3d$^3$4p configurations of Fe~V, Co~VI and Ni~VII. Additionally, radiative rates ($A$-values) have been calculated for the ... More
Vorticity in the solar photosphereOct 27 2010Aims. We use magnetic and non-magnetic 3D numerical simulations of solar granulation and G-band radiative diagnostics from the resulting models to analyse the generation of small-scale vortex motions in the solar photosphere. Methods. Radiative MHD simulations ... More
Energy levels and radiative rates for Cr-like Cu VI and Zn VIIMar 11 2016Energy levels and radiative rates (A-values) for transitions in Cr-like Cu~VI and Zn~VII are reported. These data are determined in the quasi-relativistic approach (QR), by employing a very large {\em configuration interaction} (CI) expansion which is ... More
A photospheric bright point modelMar 08 2010A magneto-hydrostatic model is constructed with spectropolarimetric properties close to those of solar photospheric magnetic bright points. Results of solar radiative magneto-convection simulations are used to produce the spatial structure of the vertical ... More
An investigation of Fe XVI emission lines in solar and stellar EUV and soft X-ray spectraAug 20 2007New fully relativistic calculations of radiative rates and electron impact excitation cross sections for Fe XVI are used to determine theoretical emission-line ratios applicable to the 251 - 361 A and 32 - 77 A portions of the extreme-ultraviolet (EUV) ... More
Electron impact excitation of N IV: calculations with the DARC code and a comparison with ICFT resultsJun 03 2016There have been discussions in the recent literature regarding the accuracy of the available electron impact excitation rates (equivalently effective collision strengths $\Upsilon$) for transitions in Be-like ions. In the present paper we demonstrate, ... More
The large- and small-scale CaII K structure of the Milky Way from observations of Galactic and Magellanic sightlinesNov 02 2015Aims: By utilising spectra of early-type stellar probes of known distances in the same region of the sky, the large and small-scale (pc) structure of the Galactic ISM can be investigated. This paper determines the variation in line strength of CaII at ... More
Optical spectroscopy of the M15 intermediate velocity cloudApr 26 2002We present echelle spectrograph observations in NaD, at resolutions of 6.2-8.5 km/s, for 11 stars located in the line-of-sight to the M15 intermediate velocity cloud, which has a radial velocity of 70 km/s. This cloud is a part of IVC Complex gp. The ... More
Plasma properties and Stokes profiles during the lifetime of a photospheric magnetic bright pointApr 01 2014Aims: to investigate the evolution of plasma properties and Stokes parameters in photospheric magnetic bright points using 3D magneto-hydrodynamical simulations and radiative diagnostics of solar granulation. Methods: simulated time-dependent radiation ... More
Large and small-scale structure of the Intermediate and High Velocity Clouds towards the LMC and SMCNov 03 2015We employ CaII K and NaI D interstellar absorption-line spectroscopy of early-type stars in the Large and Small Magellanic Clouds to investigate the large- and small-scale structure in foreground Intermediate and High Velocity Clouds (I/HVCs). These data ... More
Microflare Activity driven by Forced Magnetic ReconnectionFeb 19 2010High cadence, multiwavelength, optical observations of a solar active region are presented, obtained with the Swedish Solar Telescope. Two magnetic bright points are seen to separate in opposite directions at a constant velocity of 2.8km/s. After a separation ... More
Initial results from SECIS observations of the 2001 eclipseNov 26 2004SECIS observations of the June 2001 total solar eclipse were taken using an Fe {\sc xiv} 5303 {\AA} filter. Automated tools based on wavelet analysis was used to detect intensity oscillations on various areas of the images. Statistical analysis of the ... More
Energy levels and radiative rates for transitions in Cr-like Co IV and Ni VSep 25 2015We report calculations of energy levels and radiative rates ($A$-values) for transitions in Cr-like Co IV and Ni V. The quasi-relativistic Hartree-Fock (QRHF) code is adopted for calculating the data although GRASP (general-purpose relativistic atomic ... More
Alfven Waves in the Lower Solar AtmosphereMar 20 2009We report the detection of oscillatory phenomena associated with a large bright-point group that is 430,000 square kilometers in area and located near the solar disk center. Wavelet analysis reveals full-width half-maximum oscillations with periodicities ... More
Electron impact excitation of OII fine-structure levelsJul 24 2009Effective collision strengths for forbidden transitions among the 5 energetically lowest finestructure levels of O II are calculated in the Breit-Pauli approximation using the R-matrix method. Results are presented for the electron temperature range 100 ... More
Tracking Magnetic Bright Point Motions Through the Solar AtmosphereOct 22 2012High cadence, multi-wavelength observations and simulations are employed for the analysis of solar photospheric magnetic bright points (MBPs) in the quiet Sun. The observations were obtained with the Rapid Oscillations in the Solar Atmosphere (ROSA) imager ... More
Automated Detection and Tracking of Solar Magnetic Bright PointsMay 19 2009Magnetic Bright Points (MBPs) in the internetwork are among the smallest objects in the solar photosphere and appear bright against the ambient environment. An algorithm is presented that can be used for the automated detection of the MBPs in the spatial ... More
Ultraviolet and extreme-ultraviolet line ratio diagnostics for O IVJan 15 2009Aims: We generate theoretical ultraviolet and extreme-ultraviolet emission line ratios for O IV and show their strong versatility as electron temperature and density diagnostics for astrophysical plasmas. Methods: Recent fully relativistic calculations ... More
Stable Umbral Chromospheric StructuresDec 18 2014Aims. To understand the morphology of the chromosphere in sunspot umbra. We investigate if the horizontal structures observed in the spectral core of the Ca II H line are ephemeral visuals caused by the shock dynamics of more stable structures, and examine ... More
A study of Magnetic Bright Points in the Na I D1 lineJul 15 2010High cadence, multiwavelength, optical observations of solar magnetic bright points, captured at disk center using the ROSA and IBIS imaging systems on the Dunn Solar Telescope, are presented. Magnetic bright points manifesting in the Na I D1 core are ... More
Do all Flares have White Light Emission?Oct 08 2008High-cadence, multiwavelength optical observations of a solar active region (NOAA 10969), obtained with the Swedish Solar Telescope, are presented. Difference imaging of white light continuum data reveals a white light brightening, 2 min in duration, ... More
The Area Distribution of Solar Magnetic Bright PointsSep 13 2010Magnetic Bright Points (MBPs) are among the smallest observable objects on the solar photosphere. A combination of G-band observations and numerical simulations is used to determine their area distribution. An automatic detection algorithm, employing ... More
Electron-Impact Excitation Collision Strengths and Theoretical Line Intensities for Fine-Structure Transitions in S IIIAug 01 2013We present Maxwellian-averaged effective collision strengths for the electron-impact excitation of S III over a wide range of electron temperatures of astrophysical importance, log T(K) = 3.0-6.0. The calculation incorporates 53 fine-structure levels ... More
Observations of the interstellar medium in the Magellanic BridgeJan 31 2001Mar 20 2001We present ultraviolet and optical spectra of DI 1388, a young star in the Magellanic Bridge, a region of gas between the Small and Large Magellanic Clouds. The data have signal-to-noise ratios of 20 to 45 and a spectral resolution of 6.5 km/s. Interstellar ... More
Plasma Diagnostics of Active Region Evolution and Implications for Coronal HeatingSep 08 2005A detailed study is presented of the decaying solar active region NOAA 10103 observed with the Coronal Diagnostic Spectrometer (CDS), the Michelson Doppler Imager (MDI) and the Extreme-ultraviolet Imaging Telescope (EIT) onboard the Solar and Heliospheric ... More
Search for Rapid Changes in the Visible-Light Corona during the 21 June 2001 Total Solar EclipseSep 27 2010Some 8000 images obtained with the SECIS fast-frame CCD camera instrument located at Lusaka, Zambia, during the total eclipse of 21 June 2001 have been analyzed to search for short-period oscillations in intensity that could be a signature of solar coronal ... More
Propagating Wave Phenomena Detected in Observations and Simulations of the Lower Solar AtmosphereJan 10 2012We present high-cadence observations and simulations of the solar photosphere, obtained using the Rapid Oscillations in the Solar Atmosphere imaging system and the MuRAM magneto-hydrodynamic code, respectively. Each dataset demonstrates a wealth of magneto-acoustic ... More
Initial results from SECIS observations of the 2001 eclipseNov 24 2003Nov 26 2003SECIS observations of the June 2001 total solar eclipse were taken using an Fe xiv 5303 A filter. Existing software was modified and new code was developed for the reduction and analysis of these data. The observations, data reduction, study of the atmospheric ... More
Vortices in the solar photosphereFeb 09 2012Using numerical simulations of the magnetised solar photosphere and radiative diagnostics of the simulated photospheric models, we further analyse the physical nature of magnetic photospheric intergranular vortices. We confirm the magnetic nature of the ... More
Quiet Sun Hα Transients and Corresponding Small-Scale Transition Region and Coronal HeatingFeb 15 2016Rapid Blue- and Red-shifted Excursions (RBEs and RREs) are likely to be the on-disk counterparts of Type II spicules. Recently, heating signatures from RBEs/RREs have been detected in IRIS slit-jaw images dominated by transition-region lines around network ... More
The effect of ionization on the populations of excited levels of C IV and C V in tokamak edge plasmasMay 13 2013The main populating and depopulating mechanisms of the excited energy levels of ions in plasmas with densities <1023-1024 m-3 are electron collisional excitation from the ion's ground state and radiative decay, respectively, with the majority of the electron ... More
A search for line intensity enhancements in the far-UV spectra of active late-type stars arising from opacitySep 02 2011Radiative transfer calculations have predicted intensity enhancements for optically thick emission lines, as opposed to the normal intensity reductions, for astrophysical plasmas under certain conditions. In particular, the results are predicted to be ... More
Highly Ionized Sodium X-ray Line Emission from the Solar Corona and the Abundance of SodiumMay 24 2010{The \ion{Na}{x} X-ray lines between 10.9 and 11.2~\AA\ have attracted little attention but are of interest since they enable an estimate of the coronal abundance of Na to be made. This is of great interest in the continuing debate on the nature of the ... More
An investigation of Fe XV emission lines in solar flare spectraDec 22 2005Previously, large discrepancies have been found between theory and observation for Fe XV emission line ratios in solar flare spectra covering the 224-327 A wavelength range, obtained by the Naval Research Laboratory's S082A instrument on board Skylab. ... More
Metallicity and Physical Conditions in the Magellanic BridgeJan 16 2008We present a new analysis of the diffuse gas in the Magellanic Bridge (RA>3h) based on HST/STIS E140M and FUSE spectra of 2 early-type stars lying within the Bridge and a QSO behind it. We derive the column densities of HI (from Ly\alpha), NI, OI, ArI, ... More
Line intensity enhancements in stellar coronal X-ray spectra due to opacity effectsMar 21 2008Context. The I(15.01 A)/I(16.78 A) emission line intensity ratio in Fe XVII has been reported to deviate from its theoretical value in solar and stellar X-ray spectra. This is attributed to opacity in the 15.01 A line, leading to a reduction in its intensity, ... More
High-Frequency Oscillations in a Solar Active Region observed with the Rapid Dual ImagerJul 18 2007Oct 01 2007High-cadence, synchronized, multiwavelength optical observations of a solar active region (NOAA 10794) are presented. The data were obtained with the Dunn Solar Telescope at the National Solar Observatory/Sacramento Peak using a newly developed camera ... More
An assessment of Fe XX - Fe XXII emission lines in SDO/EVE data as diagnostics for high density solar flare plasmas using EUVE stellar observationsFeb 28 2017The Extreme Ultraviolet Variability Experiment (EVE) on the Solar Dynamics Observatory obtains extreme-ultraviolet (EUV) spectra of the full-disk Sun at a spectral resolution of ~1 A and cadence of 10 s. Such a spectral resolution would normally be considered ... More
Solar coronal observations at high frequenciesNov 22 2001The Solar Eclipse Coronal Imaging System (SECIS) is a simple and extremely fast, high-resolution imaging instrument designed for studies of the solar corona. Light from the corona (during, for example, a total solar eclipse) is reflected off a heliostat ... More
Flare X-ray observations of AB Dor: evidence for Stellar Coronal OpacityFeb 03 2005X-ray spectra of the late-type star AB Dor, obtained with the XMM-Newton satellite are analysed. AB Dor was particularly active during the observations. An emission measure reconstruction technique is employed to analyse flare and quiescent spectra, with ... More
Discovery of Spatial Periodicities in a Coronal Loop using Automated Edge-Tracking AlgorithmsFeb 14 2008A new method for automated coronal loop tracking, in both spatial and temporal domains, is presented. Applying this technique to TRACE data, obtained using the 171 Angstrom filter on 1998 July 14, we detect a coronal loop undergoing a 270s kink-mode oscillation, ... More
Multiwavelength observations of the M15 intermediate velocity cloudJun 21 2002We present Westerbork Synthesis Radio Telescope HI images, Lovell Telescope multibeam HI wide-field mapping, Wisconsin H-alpha Mapper facility images, William Herschel Telescope longslit echelle CaII observations, and IRAS ISSA 60 and 100 micron coadded ... More
Kelvin-Helmholtz instability in solar chromospheric jets: theory and observationAug 04 2016Using data obtained by the high resolution CRisp Imaging SpectroPolarimeter instrument on the Swedish 1-m Solar Telescope, we investigate the dynamics and stability of quiet-Sun chromospheric jets observed at disk center. Small-scale features, such as ... More
Eclipse observations of high-frequency oscillations in active region coronal loopsMay 13 2003One of the mechanisms proposed for heating the corona above solar active regions is the damping of magnetohydrodynamic (MHD) waves. Continuing on previous work, we provide observational evidence for the existence of high-frequency MHD waves in coronal ... More
A failed filament eruption inside a coronal mass ejection in active region 11121Feb 24 2013We study the formation and evolution of a failed filament eruption observed in NOAA active region 11121 near the southeast limb on November 6, 2010. We use a time series of SDO/AIA 304, 171, 131, 193, 335, 94 {\AA} images, SDO/HMI magnetograms, plus ROSA ... More
The effect of dust obscuration in RR Tel on optical and IR long-term photometry and Fe II emission linesMar 07 2006Infrared and optical photometric and spectroscopic observations of the symbiotic nova RR Tel are used to study the effects and properties of dust in symbiotic binaries containing a cool Mira component, as well as showing "obscuration events" of increased ... More
The Source of Three-minute Magneto-acoustic Oscillations in Coronal FansAug 15 2012We use images of high spatial, spectral and temporal resolution, obtained using both ground- and space-based instrumentation, to investigate the coupling between wave phenomena observed at numerous heights in the solar atmosphere. Intensity oscillations ... More
Iron abundances from optical Fe III absorption lines in B-type stellar spectraOct 17 2007The role of optical Fe III absorption lines in B-type stars as iron abundance diagnostics is considered. To date, ultraviolet Fe lines have been widely used in B-type stars, although line blending can severely hinder their diagnostic power. Using optical ... More
A Search for High-Frequency Coronal Brightness Variations in the 21 August 2017 Total Solar EclipseMar 14 2019We report on a search for short-period intensity variations in the green-line FeXIV 530.3 nm emission from the solar corona during the 21 August 2017 total eclipse viewed from Idaho in the United States. Our experiment was performed with a much more sensitive ... More
ROSA: a high cadence, synchronized multi-camera solar imaging systemDec 21 2009Rapid Oscillations in the Solar Atmosphere (ROSA) is a synchronized, six camera high cadence solar imaging instrument developed by Queen's University Belfast. The system is available on the Dunn Solar Telescope at the National Solar Observatory in Sunspot, ... More
A non-LTE abundance analysis of the post-AGB star ROA 5701May 09 2006An analysis of high-resolution Anglo-Australian Telescope (AAT)/ University College London Echelle Spectrograph (UCLES) optical spectra for the ultraviolet (UV)-bright star ROA 5701 in the globular cluster omega Cen (NGC 5139) is performed, using non-local ... More
Opacity in the upper atmospheres of active stars II. AD LeonisFeb 20 2006We present FUV and UV spectroscopic observations of AD Leonis, with the aim of investigating opacity effects in the transition regions of late-type stars. The C III lines in FUSE spectra show significant opacity during both the quiescent and flaring states ... More
Chemical abundances in the inner 5 kpc of the Galactic diskSep 11 2000High-resolution, high signal-to-noise spectral data are presented for four young B-type stars lying towards the Galactic Centre. Determination of their atmospheric parameters from their absorption line profiles, and uvby photometric measurement of the ... More
The Origin of Type I Spicule OscillationsNov 23 2011We use images of high spatial and temporal resolution, obtained with the Rapid Oscillations in the Solar Atmosphere instrument at the Dunn Solar Telescope, to reveal how the generation of transverse waves in Type I spicules is a direct result of longitudinal ... More
The Dynamics of Rapid Redshifted and Blueshifted Excursions in the Solar Halpha lineJan 25 2015We analyse high temporal and spatial resolution time-series of spectral scans of the Halpha line obtained with the CRisp Imaging SpectroPolarimeter (CRISP) instrument mounted on the Swedish Solar Telescope. The data reveal highly dynamic, dark, short-lived ... More
High precision transit observations of the exoplanet WASP-13b with the RISE instrumentAug 19 2011WASP-13b is a sub-Jupiter mass exoplanet orbiting a G1V type star with a period of 4.35 days. The current uncertainty in its impact parameter (0 < b < 0.46) resulted in poorly defined stellar and planetary radii. To better constrain the impact parameter ... More
RHESSI and SOHO/CDS Observations of Explosive Chromospheric EvaporationSep 22 2005Dec 21 2005Simultaneous observations of explosive chromospheric evaporation are presented using data from the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) and the Coronal Diagnostic Spectrometer (CDS) onboard SOHO. For the first time, co-spatial ... More
Degree-correlation, robustness, and vulnerability in finite scale-free networksJun 28 2016Sep 07 2016Many naturally occurring networks have a power-law degree distribution as well as a non-zero degree correlation. Despite this, most studies analyzing the robustness to random node-deletion and vulnerability to targeted node-deletion have concentrated ... More
Degree-correlation, robustness, and vulnerability in finite scale-free networksJun 28 2016Feb 15 2017Many naturally occurring networks have a power-law degree distribution as well as a non-zero degree correlation. Despite this, most studies analyzing the robustness to random node-deletion and vulnerability to targeted node-deletion have concentrated ... More
Twisting Flux Tubes as a cause of Micro-Flaring ActivitySep 14 2007High-cadence optical observations of an H-alpha blue-wing bright point near solar AR NOAA 10794 are presented. The data were obtained with the Dunn Solar Telescope at the National Solar Observatory/Sacramento Peak using a newly developed camera system, ... More
Boron Abundances in Main Sequence B-type Stars: A Test of Rotational Depletion during Main Sequence EvolutionAug 15 2001Boron abundances have been derived for seven main sequence B-type stars from HST STIS spectra around the B III 2066 A line. In two stars, boron appears to be undepleted with respect to the presumed initial abundance. In one star, boron is detectable but ... More
Transition-Region Velocity Oscillations Observed by EUNIS-06Apr 10 2008Spectroscopic measurements of AR NOAA 10871, obtained with the Extreme Ultraviolet Normal Incidence Spectrograph (EUNIS) sounding rocket instrument on 2006 April 12, reveal velocity oscillations in the He II 303.8 Angstrom emission line formed at T ~ ... More
Fe XIII emission lines in active region spectra obtained with the Solar Extreme-Ultraviolet Research Telescope and SpectrographDec 18 2006Recent fully relativistic calculations of radiative rates and electron impact excitation cross sections for Fe {\sc xiii} are used to generate emission-line ratios involving 3s$^{2}$3p$^{2}$--3s3p$^{3}$ and 3s$^{2}$3p$^{2}$--3s$^{2}$3p3d transitions in ... More
Small-scale Hα Jets in the Solar ChromosphereAug 04 2011High temporal and spatial resolution observations from the Rapid Oscillations in the Solar Atmosphere (ROSA) multiwavelength imager on the Dunn Solar Telescope are used to study the velocities of small-scale H{\alpha} jets in an emerging solar active ... More
Emission lines of Fe X in active region spectra obtained with the Solar Extreme-ultraviolet Research Telescope and SpectrographJun 20 2008Fully relativistic calculations of radiative rates and electron impact excitation cross sections for Fe X are used to derive theoretical emission-line ratios involving transitions in the 174-366 A wavelength range. A comparison of these with solar active ... More
Energy levels, radiative rates and electron impact excitation rates for transitions in He-like Ga XXX, Ge XXXI, As XXXII, Se XXXIII and Br XXXIVMar 13 2013We report calculations of energy levels, radiative rates and electron impact excitation cross sections and rates for transitions in He-like Ga XXX, Ge XXXI, As XXXII, Se XXXIII and Br XXXIV. The {\sc grasp} (general-purpose relativistic atomic structure ... More
Transverse oscillations in chromospheric mottlesFeb 25 2012A number of recent investigations have revealed that transverse waves are ubiquitous in the solar chromosphere. The vast majority of these have been reported in limb spicules and active region fibrils. We investigate long-lived, quiet Sun, on-disk features ... More
Early-type stars observed in the ESO UVES Paranal Observatory Project: I -- Interstellar Na I UV, Ti II and Ca II K observationsJan 17 2006We present an analysis of interstellar Na I (lambda=3302.37\AA, 3302.98\AA), Ti II (lambda=3383.76\AA) and Ca II K (lambda=3933.66\AA) absorption features for 74 sightlines towards O- and B-type stars in the Galactic disc. The data were obtained from ... More
Characteristics of transverse waves in chromospheric mottlesOct 14 2013Using data obtained by the high temporal and spatial resolution Rapid Oscillations in the Solar Atmosphere (ROSA) instrument on the Dunn Solar Telescope, we investigate at an unprecedented level of detail transverse oscillations in chromospheric fine ... More
Attack of the Flying Snakes : Formation of Isolated HI Clouds By Fragmentation of Long StreamsJun 17 2016The existence of long (> 100 kpc) HI streams and small (< 20 kpc) free-floating HI clouds is well-known. While the formation of the streams has been investigated extensively, and the isolated clouds are often purported to be interaction debris, little ... More
The spin-orbit alignment of the transiting exoplanet WASP-3b from Rossiter-McLaughlin observationsDec 18 2009Jun 28 2010We present an observation of the Rossiter-McLaughlin effect for the planetary system WASP-3. Radial velocity measurements were made during transit using the SOPHIE spectrograph at the 1.93m telescope at Haute-Provence Observatory. The shape of the effect ... More
Stout: Cloudy's Atomic and Molecular DatabaseJun 04 2015We describe a new atomic and molecular database we developed for use in the spectral synthesis code Cloudy. The design of Stout is driven by the data needs of Cloudy, which simulates molecular, atomic, and ionized gas with kinetic temperatures 2.8 K < ... More
Transit timing variations in WASP-10b induced by stellar activity?Jan 16 2013The hot-Jupiter WASP-10b was reported by Maciejewski et al. (2011a,b) to show transit timing variations (TTV) with an amplitude of ~ 3.5 minutes. These authors proposed that the observed TTVs were caused by a 0.1 MJup perturbing companion with an orbital ... More
Iron abundances of B-type post-Asymptotic Giant Branch stars in globular clusters: Barnard 29 in M 13 and ROA 5701 in omega CenMay 15 2007High resolution optical and ultraviolet spectra of two B-type post-Asymptotic Giant Branch (post-AGB) stars in globular clusters, Barnard 29 in M 13 and ROA 5701 in omega Cen, have been analysed using model atmosphere techniques. The optical spectra have ... More
A lower mass for the exoplanet WASP-21bJun 10 2011We present high precision transit observations of the exoplanet WASP-21b, obtained with the RISE instrument mounted on 2.0m Liverpool Telescope. A transit model is fitted, coupled with an MCMC routine to derive accurate system parameters. The two new ... More
Expanded Iron UTA spectra -- probing the thermal stability limits in AGN cloudsMar 01 2013The Fe unresolved transition array (UTAs) produce prominent features in the 15-17?A wavelength range in the spectra of Active Galactic Nuclei (AGN). Here we present new calculations of the energies and oscillator strengths of inner- shell lines from Fe ... More
Emission lines of Fe XI in the 257--407 A wavelength region observed in solar spectra from EIS/Hinode and SERTSJan 20 2010Theoretical emission-line ratios involving Fe XI transitions in the 257-407 A wavelength range are derived using fully relativistic calculations of radiative rates and electron impact excitation cross sections. These are subsequently compared with both ... More
Observations of Enhanced EUV Continua During An X-Class Solar Flare Using SDO/EVEFeb 08 2012Observations of extreme-ultraviolet (EUV) emission from an X-class solar flare that occurred on 2011 February 15 at 01:44 UT are presented, obtained using the EUV Variability Experiment (EVE) onboard the Solar Dynamics Observatory. The complete EVE spectral ... More
Soft X-ray emission lines of Fe XV in solar flare observations and the Chandra spectrum of CapellaJan 26 2006Recent calculations of atomic data for Fe XV have been used to generate theoretical line ratios involving n = 3-4 transitions in the soft X-ray spectral region (52-83 A), for a wide range of electron temperatures and densities applicable to solar and ... More
Fe XI emission lines in a high resolution extreme ultraviolet spectrum obtained by SERTSApr 05 2005New calculations of radiative rates and electron impact excitation cross sections for Fe XI are used to derive emission line intensity ratios involving 3s^23p^4 - 3s^23p^33d transitions in the 180-223 A wavelength range. These ratios are subsequently ... More
Intensity enhancement of O VI ultraviolet emission lines in solar spectra due to opacityMar 06 2014Opacity is a property of many plasmas, and it is normally expected that if an emission line in a plasma becomes optically thick, its intensity ratio to that of another transition that remains optically thin should decrease. However, radiative transfer ... More
CaII K observations of QSOs in the line-of-sight to the Magellanic BridgeOct 18 2005We describe medium-resolution spectroscopic observations taken with the ESO Multi-Mode Instrument in the CaII K line (3933.661 Angstroms) towards 7 QSOs located in the line-of-sight to the Magellanic Bridge. At a spectral resolution R = 6,000, five of ... More
X-ray line coincidence photopumping in a solar flareNov 21 2017Line 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 line coincidence ... More