Journal Articles
The datasets associated with the publications below are published as electronic machine readable tables with the papers, and are accessible via the publishing Journals. (Some datasets are also available via international databases).
2022
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Wavelengths and Energy Levels of Singly Ionized Nickel (Ni II) Measured Using Fourier Transform Spectroscopy
Clear CP, Pickering JC, Nave G, Uylings P, Raassen T, ApJS 261, 35 (2022)
Publication
abstract  
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Comment on: “Hyperfine structure measurements of Co I
and Co II with Fourier transform spectroscopy” by Fu et al.
[JQSRT 2021, 107590]
Ding M & Pickering JC , JQSRT, 288, 108240 (2022)
Publication
Download Arxiv PDF
abstract  
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The Gaia-ESO Public Spectroscopic Survey: Implementation, data products, open cluster survey, science,
and legacy
Randich S et al, A & A, in press (2022)
Download Arxiv PDF
abstract  
2021
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New Ritz Wavelengths and Transition Probabilities of Parity-forbidden
[Mn II] Lines of Astrophysical Interest
Liggins FS, Pickering JC, Nave G, Kramida A, Gamrath S, Quinet P,
ApJ 907, 69 (2021)
Publication
abstract  
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Reference wavelengths of Si II, C II, Fe II, and
Ni II for quasar absorption spectroscopy
Clear C & Nave G, Mon. Not. Royal Astronomical Soc, 502 (4), 5679-5685 (2021)
Publication
Download Arxiv PDF
abstract  
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Emission spectroscopic study of an analytical glow discharge with plane
and hollow cathodes: Titanium and iron in argon discharge
Weiss Z,
Concepcion-Mairey F,
Pickering JC,
Smid P, Spectrochim. Acta B - Atomic Spectroscopy, 180,106208 (2021)
Publication
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Atomic data for the Gaia-ESO Survey
Heiter U et al, Astronomy & Astrophysics, 645, A106 (2021)
Publication
Download Arxiv PDF
Data tables
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The Spectrum and Term Analysis of Singly Ionized Manganese
Liggins FS, Pickering JC, Nave G, Ward JW, Tchang-Brillet WUL, Astrophysical J Supp, 252 (1), 10 (2021)
Publication
Download PDF
Abstract
2020
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Measurements of the Hyperfine Structure of Atomic Energy Levels in Co II
Ding ML & Pickering JC, Astrophysical J Supp, 251 (2), 24 (2020)
Publication
Download PDF
Abstract
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VizieR Online Data Catalog: Atomic data for the Gaia-ESO Survey
Heiter et al (2020)
Source Paper
Abstract
VizieR Catalogue link
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Recent advances in experimental laboratory
astrophysics for stellar astrophysics
applications and future data needs
Pickering JC, Belmonte MT, Clear CP, Liggins F, Concepcion-Mairey F,
Proceedings of the International Astronomical Union, Vol 15, Symposium S350: Laboratory Astrophysics: From Observations to Interpretation,
April 2019 , pp. 220 - 228 (2020)
Publication
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Abstract
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Charge transfer from doubly charged ions of transition elements in a
neon glow discharge: evidence based on emission spectra
Weiss Z & Pickering JC, Plasma Sources Science & Technology, 29 (4), 045025 (2020)
Publication
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2015-2019
2015
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Atomic and molecular data for optical stellar spectroscopy
Heiter U, Lind K, Asplund M, Barklem P, Bergemann M, Magrini L, Masseron T, Mikolaitis Š, Pickering J, Ruffoni M, Physica Scripta, 90 (5) Art. No. 054010 (2015) (more info PDF)
Authors: Heiter U, Lind K, Asplund M, Barklem P, Bergemann M, Magrini L, Masseron T, Mikolaitis Š, Pickering J, Ruffoni M
Abstract: High-precision spectroscopy of large stellar samples plays a crucial role
for several topical issues in astrophysics. Examples include studying the chemical structure and
evolution of the Milky Way galaxy, tracing the origin of chemical elements, and characterizing
planetary host stars. Data are accumulating from instruments that obtain high-quality spectra
of stars in the ultraviolet, optical and infrared wavelength regions on a routine basis. These
instruments are located at ground-based 2- to 10-m class telescopes around the world, in addition
to the spectrographs with unique capabilities available at the Hubble Space Telescope.
The interpretation of these spectra requires high-quality transition data for numerous species,
in particular neutral and singly ionized atoms, and di- or triatomic molecules.
We rely heavily on the continuous efforts of laboratory astrophysics groups that produce and
improve the relevant experimental and theoretical atomic and molecular data. The compilation
of the best available data is facilitated by databases and electronic infrastructures such as
the NIST Atomic Spectra Database, the VALD database, or the Virtual Atomic and Molecular Data Centre (VAMDC). We illustrate the current status of atomic data for optical stellar spectra with the example of the Gaia-ESO Public Spectroscopic Survey. Data sources for 35 chemical elements were reviewed in an effort
to construct a line list for a homogeneous abundance analysis of up to 105 stars.
Copyright (2015) The American Astronomical Society.
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Publication
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2014
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Fe I Oscillator Strengths for Transitions from High-Lying Even-Parity Levels
Den Hartog EA, Ruffoni MP, Lawler JE, Pickering JC, Lind K, Brewer NR, ApJS 215(2), 23 (2014) (more info PDF)
Authors: Den Hartog EA, Ruffoni MP, Lawler JE, Pickering JC, Lind K, Brewer NR
Abstract: New radiative lifetimes, measured to ±5 % accuracy, are reported for 31
even-parity levels of Fe I ranging from 45061 cm-1 to 56842 cm-1.
These lifetimes have been measured using single-step and two-step time-resolved laser-induced fluorescence on a slow atomic
beam of iron atoms. Branching fractions have been attempted for all of these levels, and completed for 20 levels. This set
of levels represents an extension of the collaborative work reported
in Ruffoni et al. (2014).
The radiative lifetimes combined with the branching fractions yields new oscillator strengths for 203 lines
of Fe I. Utilizing a 1D-LTE model of the solar photosphere, spectral syntheses
for a subset of these lines which are unblended in the solar spectrum yields a mean iron abundance
of <log[ε(Fe)]> = 7.45 ± 0.06.
Copyright (2014) The American Astronomical Society.
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Publication
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Fe I Oscillator Strengths for the Gaia-ESO Survey
Ruffoni MP, Den Hartog EA, Lawler JE, Brewer NR, Lind K, Nave G,
Pickering JC, Mon. Not. R. Astron. Soc., 441(4), 3127 (2014)
(more info PDF)
Authors: Ruffoni MP, Den Hartog EA, Lawler JE, Brewer NR, Lind K, Nave G, Pickering JC
Abstract: The Gaia-ESO Public Spectroscopic Survey (GES) is conducting a large-scale study of multi-element chemical abundances of some 100,000 stars in the Milky Way with the ultimate aim of quantifying the formation history and evolution of young, mature and ancient Galactic populations. However, in preparing for the analysis of GES spectra, it has been noted that atomic oscillator strengths of important Fe I lines required to correctly model stellar line intensities are missing from the atomic database. Here, we present new experimental oscillator strengths derived from branching fractions and level lifetimes, for 142 transitions of Fe I between 3526 Å and 10864 Å, of which at least 38 are urgently needed by GES. We also assess the impact of these new data on solar spectral synthesis and demonstrate that for 36 lines that appear unblended in the Sun, Fe abundance measurements yield a small line-by-line scatter (0.08 dex) with a mean abundance of 7.44 dex in good agreement with recent publications.
(C) 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.
Links:
Publication
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Transition rate diagrams - A new approach to the study of selective excitation processes:
The spectrum of manganese in a Grimm-type glow discharge
Weiss Z., Steers E.B.M., Pickering J.C., Mushtaq S
Spectrochim. Ac. B - At. Spect., 92, 70 (2014)
(more info coming soon PDF)
Authors: Weiss Z., Steers E.B.M., Pickering J.C., Mushtaq S.
Abstract:
Awaiting information
Copyright (2014)
Links:
Awaiting Download PDF
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Excitation of higher levels of singly charged copper ions in argon and neon glow
discharges
Weiss Z., Steers E.B.M., Pickering J.C., Hoffmann V., and Mushtaq S., J Analyt. Atomic Spectrometry, 29 (12), 2256 - 2261 (2014)
(more info coming soon PDF)
Authors: Weiss Z., Steers E.B.M., Pickering J.C., Hoffmann V., and Mushtaq S.
Abstract:
Awaiting information
Copyright (2014) JAAS
Links:
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Enhancement of analyte atomic lines with excitation energies of about 5 eV in the presence
of molecular gases in analytical glow discharges
Mushtaq S., Steers E.B.M., Pickering J.C. & Šmid P.
J Analytical Atomic Spectrom., 29, 2022-2026 (2014)
(more info coming soon PDF)
Authors:Mushtaq S., Steers E.B.M., Pickering J.C. & Šmid P.
Abstract:
Awaiting information
Copyright (2014) JAAS
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Effect of small quantities of oxygen in a neon glow discharge
Mushtaq S., Steers E.B.M., Pickering J.C. & Weinstein V.
J. Analytical Atomic Spectrom., 29, 2027-2041 (2014)
(more info coming soon PDF)
Authors: Mushtaq S., Steers E.B.M., Pickering J.C. & Weinstein V.
Abstract:
Awaiting information
Copyright (2014) JAAS
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Excitation and transition rate diagrams of singly ionized iron in analytical glow discharges in
argon, neon and an argon–hydrogen mixture
Weiss Z., Steers E.B.M., Pickering J.C. & Mushtaq S.
J. Analytical. At. Spectrom., 29, 2078-2090 (2014)
(more info coming soon PDF)
Authors: Weiss Z., Steers E.B.M., Pickering J.C. & Mushtaq S.
Abstract:
Awaiting information
Copyright (2014) JAAS
Links:
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2013
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Infrared Laboratory Oscillator Strengths of Fe I in the H-Band
Ruffoni MP, Allende Prieto C, Nave G, Pickering JC
Astrophysical Journal, 779 pp17 (2013)
(more info PDF)
Authors: Ruffoni MP, Allende Prieto C, Nave G, Pickering JC
Abstract:
We report experimental oscillator strengths for 28 infrared Fe I transitions, for which no previous experimental
values exist. These transitions were selected to address an urgent need for oscillator strengths
of lines in the H-band (between 1.4 μm and 1.7 μm) required for the analysis of spectra obtained
from the Sloan Digital Sky Survey (SDSS-III) Apache Point Galactic Evolution Experiment (APOGEE).
Upper limits have been placed on the oscillator strengths of an additional 7 transitions, predicted
to be significant by published semi-empirical calculations, but not observed to be so.
Copyright (2013) The American Astronomical Society
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Publication
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The Spectrum and Term Analysis of V II
Thorne AP, Pickering JC and Semeniuk JI,
Astrophysical Journal Supplement Series, 207 (1) Art UNSP 13 (2013)
(more info PDF)
Authors: Thorne AP, Pickering JC and Semeniuk JI
Abstract:
The spectrum and extended term analysis of V II are presented. Fourier transform spectrometry was used
to record high resolution spectra of singly ionized vanadium in the region 1492-5800 angstrom
(67020-17260 cm(-1)) with vanadium-neon and vanadium-argon hollow cathode lamps as sources.
The wavenumber uncertainty for the center of gravity of the strongest lines is typically 0.002 cm(-1),
an improvement of an order of magnitude over previous measurements. Most of the lines exhibit partly
resolved hyperfine structure. The V II energy levels in the 1985 compilation of Sugar and Corliss have been
confirmed and revised, with the exception of the high-lying 4f levels and eight of the lower levels.
Thirty-nine of the additional eighty-five high levels published by Iglesias et al. have also been confirmed
and revised, and three of their missing levels have been found. The energy uncertainty of the revised levels
has been reduced by about an order of magnitude.
In total, 176 even levels and 233 odd levels are presented. Wavenumbers and classifications are given for 1242 V II lines.
Copyright (2013) The American Astronomical Society
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Atomic data for iron-group elements of astrophysical interest
Nave G, Sansonetti CJ, Pickering JC, Ruffoni MP, Thorne AP, Liggins FS, AIP Conf. Proc., 1545 pp.
27 (2013) (more info Publication)
Authors: Nave G, Sansonetti CJ, Pickering JC, Ruffoni MP, Thorne AP, Liggins FS
Abstract: The joint project between NIST and Imperial College London to measure spectra
of singly-ionized iron-group elements using Fourier transform and high-resolution grating spectroscopy is
described.
Copyright (2013) AIP Publishing LLC.
Links:
Publication
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Accurate Ritz wavelengths of parity-forbidden [Co II] and [V II] lines of astrophysical interest
Ruffoni MP and Pickering JC,
Astrophysical Journal Supplement, 207 pp20 (2013)
(more info PDF)
Authors: Ruffoni MP and Pickering JC
Abstract:
We report a comprehensive list of accurate Ritz wavelengths for parity-forbidden [Co II] and [V II]
lines obtained from the analysis of energy levels measured in the laboratory with Fourier transform
emission spectroscopy. Such lines, particularly those in the infrared, are in demand for the analysis
of low-density astrophysical plasmas in and around objects such as planetary nebulae, star-forming
regions, and active galactic nuclei. Transitions between all known metastable levels of Co II and
V II are included in our analysis, producing wavelengths for 1477 [V II] lines and 782 [Co II] lines.
Of these, 170 [V II] lines and 171 [Co II] lines arise from transitions with calculated transition
probabilities greater than 1 x 10-2 s-1 and upper level excitations of less than 5 eV, and thus are
likely to be observed in astrophysical spectra.
Copyright (2013) The American Astronomical Society
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2012
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Recent advances in measurement of the water vapour continuum in the far-infrared spectral region
PD Green, SM Newman, RJ Beeby, JE Murray, JC Pickering & JE Harries, Phil. Trans. Roy. Soc. A, 370(1968), 2637-2655 (2012)
(more info PDF)
Authors: PD Green, SM Newman, RJ Beeby, JE Murray, JC Pickering & JE Harries
Abstract:
We present a new derivation of the foreign-broadened water vapour continuum in the far-infrared
(far-IR) pure rotation band between 24 μm and 120 μm (85–420 cm−1) from field data collected
in flight campaigns of the Continuum Absorption by Visible and IR radiation and Atmospheric Relevance
(CAVIAR) project with Imperial College's Tropospheric Airborne Fourier Transform Spectrometer (TAFTS)
far-IR spectro-radiometer instrument onboard the Facility for Airborne Atmospheric Measurement (FAAM)
BAe-146 research aircraft; and compare this new derivation with those recently published in the literature
in this spectral band. This new dataset validates the current
Mlawer–Tobin-Clough–Kneizys–Davies (MT-CKD) 2.5 model parametrization above 300 cm−1,
but indicates the need to strengthen the parametrization below 300 cm−1, by up to 50 per
cent at 100 cm−1. Data recorded at a number of flight altitudes have allowed measurements within
a wide range of column water vapour environments, greatly increasing the sensitivity of this analysis
to the continuum strength.
Copyright (2012) The Royal Society.
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2011
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Effects of traces of oxygen on Grimm-type glow discharges in argon
Mushtaq S, Steers EBM, Pickering JC, et al., JAAS 26 766 (2011)
(more info PDF)
Authors: Mushtaq S, Steers EBM, Pickering JC, Gusarova T, Smid P, Weinstein V
Abstract:
We report results of studies using Fourier Transform Optical Emission Spectroscopy (FT-OES) to investigate the effects of added oxygen (0.04–0.8% v/v) on observed spectra from a Grimm-type glow discharge, generated in argon plasma with a pure iron sample. Significant changes in the sputter rate
and the intensities of atomic lines of the carrier gas and sample in the presence of oxygen are discussed in detail; these changes are greater than those observed with Ar/H2 and Ar/N2 mixtures. A detailed study of spectral line profiles shows changes in self-absorption of Ar I lines due to O2 and H2 traces. The
sputter rate for a given Ar/O2 gas mixture is found not to be proportional to current.
Copyright (2011) Royal Society of Chemistry.
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Publication
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High-resolution photoabsorption cross section measurements of SO2 at 198 K from 213 to
325 nm
Blackie D, Blackwell-Whitehead R, Stark G, Pickering JC, Smith PL. Rufus J,Thorne AP
JGR VOL. 116, E03006 (2011)
(more info PDF)
Authors: Blackie D, Blackwell-Whitehead R, Stark G, Pickering JC, Smith PL. Rufus J,Thorne AP
Abstract:
SO2 plays an important role in the atmospheric chemistry of the Earth, Venus, and
Io. This paper presents photoabsorption cross sections of SO2 from 213 to 325 nm at
198 K, encompassing the C1B2 − X1A1 and B1B1 − X1A1 electronic bands. These
measurements are part of a series of measurements over the 160 to 300 K temperature
range between 190 and 325 nm. The cross sections have been measured at high resolution
(lambda/delta lambda ≈ 450,000) using Fourier transform spectrometry and are compared to other
high‐resolution measurements in the literature.
Copyright (2011) American Geophysical Union.
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- The Spectrum and Term Analysis of V I
Thorne AP, Pickering JC, Semeniuk J, ApJS 192 11 (2011) doi: 10.1088/0067-0049/192/1/11
(more info PDF)
Authors: Thorne AP, Pickering JC, Semeniuk J
Abstract:
High-resolution spectra of neutral vanadium have been recorded by Fourier transform spectrometry in the region
1492-28600 Å (67020-3496 cm–1) with vanadium-neon and vanadium-argon hollow cathode lamps as sources.
Most of the lines exhibit fully or partly resolved hyperfine structure, but the wavenumber uncertainty for the center of gravity
of the strongest lines is 0.002 cm–1. Of the previously published energy levels of V I, 72 have been revised
and 37 discarded. In addition, 89 new levels have been found. In total 346 odd levels and 198 even levels are presented.
Wavenumbers and classifications are given for 3130 V I lines.
Copyright (2011) The American Astronomical Society.
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- Infrared Mn I laboratory oscillator strengths for the study of late type stars and ultracool
dwarfs
Blackwell-Whitehead R., Pavlenko Y,V, Nave G., Pickering J.C., Jones H.R.A., Lyubchik
Y. and Nilsson H.,Astronomy & Astrophysics,A&A 525 A44 (2011)
(more info PDF)
Authors: Blackwell-Whitehead R., Pavlenko Y,V, Nave G., Pickering J.C., Jones H.R.A., Lyubchik
Y. and Nilsson H.
Abstract:
Aims. The aim of our new laboratory measurements is to measure accurate absolute oscillator strengths
for neutral manganese transitions in the infrared needed for the study of late-type stars and ultracool dwarfs.
Methods. Branching fractions have been measured by high resolution Fourier transform spectroscopy
and combined with radiative level lifetimes in the literature to yield oscillator strengths.
Results. We present experimental oscillator strengths for 20 Mn I transitions in the wavelength range 3216 to 13997 Å,
15 of which are in the infrared. The transitions at 12899 Å and 12975 Å are observed as strong features in the spectra
of late-type stars and ultracool dwarfs. We have fitted our calculated spectra to the observed Mn I
lines in spectra of late-type stars. Using the new experimentally measured Mn I log(gf) values together with existing data
for Mn I hyperfine structure splitting factors we determined the manganese abundance to be log N(Mn) = −6.65 ± 0.05 in
the atmosphere of the Sun, log N(Mn) = 6.95 ± 0.20 in the atmosphere of Arcturus, and log N(Mn) = −6.70 ± 0.20
in the atmosphere of M 9.5 dwarf 2MASSW 0140026+270150.
Copyright (2010) ESO
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Laboratory measurements of oscillator strengths and their astrophysical applications
Pickering JC, Blackwell-Whitehead R, Thorne AP, et al., Can. J. Phys 89 pp. 387 (2011)
(more info)
Authors: Pickering JC, Blackwell-Whitehead R, Thorne AP, Ruffoni MP, Holmes CE
Abstract: We present an overview of current needs for accurate laboratory atomic transition probabilities (loggfs) for astrophysical applications, particularly for iron group element spectra in the IR, optical, UV and VUV spectral regions. Examples are given of our recent measurements, undertaken using the combination of high resolution Fourier transform spectrometry and time resolved laser induced fluorescence. Laboratory measured loggfs are particularly important for determination of elemental abundances in astrophysical objects. With new facilities, telescopes and spectrographs, access to underexplored regions (IR, vacuum UV,VUV), and new stellar atmosphere models (e.g. 3D, NLTE), astronomers are tackling problems ranging from determining accurate elemental abundances in the Sun, studying Galactic chemical evolution, to low mass stars and exoplanets. Such advances require improved accuracy and completeness of the atomic database for meaningful analyses of astrophysical spectra.
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Publication
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2010
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New atomic data for astrophysics by high-resolution spectroscopy
Ruffoni MP, Pickering JC, Thorne AP, et al., Proceedings of the NASA laboratory astrophysics workshop (2010) (more info)
Authors: Ruffoni MP, Pickering JC, Thorne AP, Holmes CE, Smith PL
Abstract: We report a summary of recent significant improvements to atomic and molecular data obtained through
high resolution Fourier transform spectrometry at Imperial College London. These primarily include wavelengths, energy levels,
and oscillator strengths of neutral, singly, and doubly ionised iron-group atoms of astrophysical significance.
Copyright (2010)
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- Measurement and simulation of mid- and far-infrared spectra
in the presence of cirrus
C. V. Cox, J. E. Harries, J. P. Taylor, P. D. Green, A. J. Baran, J. C. Pickering,
A. E. Last and J.E. Murray, Q. J. R. Meteorol. Soc. 136: 718–739, April 2010 Part A (more info)
Authors: C. V. Cox, J. E. Harries, J. P. Taylor, P. D. Green, A. J. Baran, J. C. Pickering,
A. E. Last and J.E. Murray
Abstract:
Observed far-infrared and mid-infrared radiance spectra measured in situ above
cirrus with both the Tropospheric Airborne Fourier Transform Spectrometer
(TAFTS) and the Airborne Research Interferometer Evaluation System (ARIES) are
presented. Two sets of upwelling spectra between wavenumbers 100 and 1415cm−1
taken over ice cloud of visible optical thickness 0.1 and 0.3 are shown. These
observations address the need for more measurements of radiance from cirrus,
particularly in the far infrared, where experimental data are lacking. A test of
consistency in modelling in both the far infrared and mid infrared is performed
by fitting a model calculation of radiances in the infrared window region, and
comparing with the measured radiances. In this consistency check, the sampling
of the surrounding atmosphere and the cloud is given extensive consideration.
The model was not able to consistently reproduce the observed radiance across
the entire region, and was particularly poor in the 330–600cm-1 region of the far
infrared. Possible causes are thought to be primarily model input uncertainties
arising from inadequate sampling of cloud and atmosphere.
RoyalMeteorological Society and Crown Copyright (2010)
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- Accurate laboratory wavelengths of the 1910 Å Ti II resonance transitions relevant to studies
of possible variations of the fine structure constant
Ruffoni MP, Pickering JC, ApJ. 725 pp. 424 (2010) (more info PDF)
Authors: Ruffoni MP, Pickering JC
Abstract: In recent years, the analysis of absorption lines in quasi-stellar object (QSO) spectra, using
the many-multiplet (MM) method, has provided evidence for space-time variations in the fine-structure constant, α. Future studies
aim to reduce systematic errors in these measurements by considering a greater number of transitions, but this is only possible for
lines where high-precision laboratory standards exist. Two transitions of high importance for future MM analyses, but which currently
lack accurately measured wavelengths, are the Ti II transitions observed at 1910 Å. We report accurate measurements of these
transitions by high-resolution Fourier transform spectroscopy, giving line wavenumbers of 52329.889 ± 0.001 cm-1 and
52339.240 ± 0.001 cm-1. Lines from other important Ti II, Mg I, Mg II, and Zn II transitions were measured
simultaneously; minimising their relative wavenumber uncertainties, and permitting the newly measured 1910 Å Ti II line wavenumbers
to be linked directly to lines from other studies.
Copyright (2010) The American Astronomical Society.
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- NLTE analysis of Co I/Co II lines in spectra of cool stars with new laboratory hyperfine splitting constants
Maria Bergemann, Juliet C. Pickering, and Thomas Gehren, MNRAS, 401 (2) 1334-1346 (2010)
(more info PDF)
Authors: Maria Bergemann, Juliet C. Pickering, and Thomas Gehren
Abstract: The analysis of stellar abundances for odd-Z Fe-peak elements requires accurate non-local
thermodynamic equilibrium (NLTE) modelling of spectral lines fully taking into account the
hyperfine structure (HFS) splitting of lines. Here, we investigate the statistical equilibrium of
Co in the atmospheres of cool stars and the influence of NLTE and HFS on the formation
of Co lines and abundances. Significant departures from LTE level populations are found for
Co I; number densities of excited states in Co II also differ from LTE at low metallicity. The
NLTE level populations are used to determine the abundance of Co in solar photosphere,
log ε = 4.95 ± 0.04 dex, which is in agreement with that in C I meteorites within the combined
uncertainties. The spectral lines of Co I were calculated using the results of recent measurements
of hyperfine interaction constants by UV Fourier transform spectrometry. For Co II, the
first laboratory measurements of HFS A and B factors were performed. These highly accurate
A factor measurements (errors of the order of 3–7 per cent) allow, for the first time, reliable
modelling of Co II lines in the solar and stellar spectra and, thus, a test of the Co I/Co II ionization
equilibrium in stellar atmospheres. A differential abundance analysis of Co is carried
out for 18 stars in the metallicity range −3.12 < [Fe/H] < 0. The abundances are derived
by the method of spectrum synthesis. At low [Fe/H], NLTE abundance corrections for Co I
lines are as large as +0.6, . . . , + 0.8 dex. Thus, LTE abundances of Co in metal-poor stars are
severely underestimated. The stellar NLTE abundances determined from the single UV line of
Co II are lower by 0.5–0.6 dex. The discrepancy might be attributed to possible blends that
have not been accounted for in the solar Co II line and its erroneous oscillator strength. The
increasing [Co/Fe] trend in metal-poor stars, as calculated from the Co I lines under NLTE,
can be explained if Co is overproduced relative to Fe in massive stars. The models of Galactic
chemical evolution are wholly inadequate to describe this trend suggesting that the problem
is in supernova yields.
Copyright (2009) RAS
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- A detailed comparison of spectral line intensities with plane and hollow cathodes in a Grimm type glow discharge source
Weinstein V, Steers EBM, Smid P, Pickering JC, Mushtaq S., J. Analytical Atomic Spectrometry (JAAS), 25 (8) 1283-1289 (2010) (more info PDF)
Authors: Weinstein V, Steers EBM, Smid P, Pickering JC, Mushtaq S.
Abstract:
The hollow cathode discharge was investigated and compared with the plane cathode discharge in a Grimm-type source studying a
large number of lines with iron and titanium as cathode materials in argon plasma. The high resolution Fourier Transform Spectrometer
(FTS) at Imperial College (IC) was used for recording spectra. The intensity changes for atomic and ionic lines of iron, titanium
and argon are discussed, whereby clear trends in intensity increase and reduction according to the excitation energies of the
emission lines are identified. Differences in line profiles in spectra using the hollow and plane cathodes were detected.
The comparison between the hollow (10-15 mm deep) and shallow (2 mm deep) cathodes gives additional information about the depth
influence on the hollow cathode effect. The extended study presented in this paper is a further step towards a better understanding
of the discharge processes in the glow discharge.
Copyright (2010) Royal Society of Chemistry.
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- Laboratory measurements of oscillator strengths and their astrophysical applications
Pickering JC, Blackwell-Whitehead R, Thorne AP, et al., Can. J. Phys (ASOS10 Ed.) submitted (2010) (more info)
Authors: Pickering JC, Blackwell-Whitehead R, Thorne AP, Ruffoni MP, Holmes CE
Abstract: We present an overview of current needs for accurate laboratory atomic transition probabilities (loggfs)
for astrophysical applications, particularly for iron group element spectra in the IR, optical, UV and VUV spectral regions.
Examples are given of our recent measurements, undertaken using the combination of high resolution Fourier transform spectrometry
and time resolved laser induced fluorescence. Laboratory measured loggfs are particularly important for determination of elemental
abundances in astrophysical objects. With new facilities, telescopes and spectrographs, access to underexplored regions (IR, vacuum
UV,VUV), and new stellar atmosphere models (e.g. 3D, NLTE), astronomers are tackling problems ranging from determining accurate
elemental abundances in the Sun, studying Galactic chemical evolution, to low mass stars and exoplanets. Such advances require
improved accuracy and completeness of the atomic database for meaningful analyses of astrophysical spectra.
Links:
Publication
|
2009
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High-resolution photoabsorption cross-section measurements of SO2 at 160 K between 199 and 220 nm
J. Rufus, G. Stark, A. P. Thorne, J. C. Pickering, R. J. Blackwell-Whitehead, D. Blackie and Peter L. Smith,
Journal of Geophysical Research, 14, E06003, doi:10.1029/2008JE003319 (2009)
(more info PDF)
Authors: Rufus J, Stark G, Thorne AP, Pickering JC, Blackwell-Whitehead RJ, Blackie D and Smith PL
Abstract:
Photoabsorption cross sections of sulfur dioxide over a range of temperatures are required to interpret observations
and to support models of the atmospheres of Io and Venus. We report high-resolution (lambda/Delta lambda approximate to 450,000)
photoabsorption cross-section measurements by Fourier transform spectrometry of SO2
at 160 K in the wavelength
region 199 to 220 nm, which encompasses the strongest features in the prominent
(C) over tilde (1) B2 -(X) over tilde (1)A1 system. Our results are compared with literature values obtained at
lower resolutions and with 295 K cross sections recorded earlier with the same instrument.
Copyright (2010) Amer Geophysical Union
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2008
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Cross Sections and Reaction Rates for Comparative Planetary Aeronomy
Huestis DL, Bougher SW, Fox JL, Galand M, Johnson RE, Moses J, Pickering JC,
Space Science Reviews, 139 (1-4), 63-105, (2008)
(more info PDF)
Authors: Huestis DL, Bougher SW, Fox JL, Johnson RE, Moses J, Pickering JC,
Abstract:
In this chapter we describe the current knowledge of a selection of collision
processes and chemical reactions of importance to planetary aeronomy. Emphasis is placed
on critical evaluation of what we know and what we wish we knew about fundamental
processes required for interpretation, explanation, and modeling of atmospheric observations.
Copyright (2008)
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- Reference ultraviolet wavelengths of Cr III measured by Fourier transform spectrometry
Smillie DG, Pickering JC & Smith PL, Monthly Notices of the Royal Astronomical Society, 390 (2), 733-740 (2008)
(more info PDF)
Authors: Smillie DG, Pickering JC & Smith PL
Abstract:
We report Cr III ultraviolet (UV) transition wavelengths measured using a high-resolution Fourier transform spectrometer (FTS),
for the first time, available for use as wavelength standards. The doubly ionized iron group element spectra dominate the observed
opacity of hot B stars in the UV, and improved, accurate, wavelengths are required for the analysis of astronomical spectra.
The spectrum was excited using a chromium-neon Penning discharge lamp and measured with the Imperial College vacuum ultraviolet FTS.
140 classified 3d34s-3d34p Cr III transition lines, in the spectral range 38 000 to 49 000 cm-1 (2632 to 2041 angstrom),
the strongest having wavelength uncertainties less than one part in 107, are presented.
Copyright (2008) RAS.
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- The effect of hydrogen and nitrogen on emission spectra of iron and titanium atomic lines in analytical glow
discharges
Smid P, Steers E, Weiss Z, Pickering J & Hoffmann V,JAAS, J Analytical Atomic Spectrometry, 23 (9), 1223-1233 (2008)
(more info PDF)
Authors: Smid P, Steers E, Weiss Z, Pickering J & Hoffmann V
Abstract:
It is now well known that traces of molecular gases such as hydrogen or nitrogen can affect significantly
the electrical characteristics, sputtering rates and relative intensities of emission lines in glow discharge
optical emission spectrometry (GD-OES). These changes, caused by the molecular gases which are very
often present in the discharge for various reasons, have a serious impact on the accuracy of analytical
results. Therefore, it is important to describe these effects in detail and to try to understand the
processes involved. The results presented in this paper focus on the effects of hydrogen and nitrogen on
intensities of atomic emission lines of iron and titanium. In the case of hydrogen, when intensity ratios
(intensities measured in argon–hydrogen relative to those measured in pure argon) are plotted against
the excitation energies of the lines, these intensity ratios increase with the excitation energy between
approx. 3 and 5 eV for both elements studied. Furthermore, in the case of iron, several emission lines
with the excitation energy between 5.3 and 5.6 eV are strongly enhanced in the presence of hydrogen. It
has been also observed that this effect is more pronounced at lower currents. On the other hand, it has
been found that nitrogen does not have any similar effect: the gradient of the intensity ratios of both
elements is negligible or even negative and no emission lines are enhanced in the presence of nitrogen.
A comparison was also made between direct current and radiofrequency powered glow discharges and
very similar trends have been obtained.
Copyright (2008)The Royal Society of Chemistry.
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2007
- A revision of the solar manganese abundance using new and remeasured laboratory oscillator strengths
Blackwell-Whitehead RJ, Bergemann M, A&A 472, L43–L46 (2007)
(more info PDF)
Authors: Blackwell-Whitehead RJ, Bergemann M
Abstract:
Context. The solar photospheric element abundances are generally in good agreement with the meteoritic CI chondrite abundances,
with the exception of a small number of elements including manganese. The solar photospheric abundances, determined using model
atmospheres, include laboratory oscillator strengths where available. However, the current laboratory database for Mn I oscillator
strengths is derived from several different laboratory observations determined from several different laboratory techniques. The uncertainty
in the solar photospheric manganese abundance and the difference between it and the meteoritic CI chondrite abundance
may just be an artefact of inaccurate laboratory data.
Aims. The aim of our new laboratory measurements is to measure a self consistent set of accurate absolute oscillator strengths and
use the new laboratory data to re-evaluate the solar manganese abundance.
Methods. New and more accurate oscillator strengths have been determined by combining branching fractions with previously measured
energy level lifetimes. Using the new laboratory data, the solar photospheric abundance of manganese has been determined with
theoretical and semi-empirical model atmospheres, MAFAGS-ODF and Holweger & Müller, respectively.
Results. We present experimental oscillator strengths for 94 Mn I transitions covering the wavelength range 2384 to 17 744 Å. Using
22 relatively un-blended solar Mni transitions, we determine the photospheric abundance of manganese to be log ε = 5.37±0.05 dex.
Conclusions. The new value is in good agreement with previous photospheric abundance determinations. The implications for the
solar photospheric and meteoritic CI chondrite abundance is discussed.
Copyright (2007) ESO
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2006
- Experimental Ti I oscillator strengths and their application to cool star analysis
Blackwell-Whitehead RJ, Lundberg H, Nave G, Pickering JC, Jones HRA, Lyubchik Y, Pavlenko YV
and Viti S, Mon. Not. R. Astron. Soc. 373, 1603-1609 (2006)
(more info PDF)
Authors: Blackwell-Whitehead RJ, Lundberg H, Nave G, Pickering JC, Jones HRA, Lyubchik Y, Pavlenko YV, Viti S
Abstract:
We report experimental oscillator strengths for 88 Ti I transitions covering the wavelength range 465-3892 nm, 67 of which had
no previous experimental values. Radiative lifetimes for 13 energy levels, including the low energy
levels 3d2 (3F) 4s4p (3)P) z5Dj degrees have been measured using time-resolved laser-induced fluorescence.
Intensity-calibrated Ti I spectra have been measured using Fourier transform spectroscopy to determine branching fractions for
the decay channels of these levels. The branching fractions are combined with the radiative lifetimes to yield absolute transition
probabilities and oscillator strengths. Our measurements include 50 transitions in the previously unobserved infrared region
lambda > 1.0 mu m, a region of particular interest to the analysis of cool stars and brown dwarfs.
Copyright (2006) RAS
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- Investigation of the hyperfine structure of Ta I lines (X)
Jaritz N, Windholz L, Zaheer U, Farooq M, Arcimowicz B, Engleman Jr. R, Pickering JC, J¨ager H &
Guth¨ohrlein GH, Physica Scripta 74, 211-217 (2006)
(more info PDF)
Authors: Jaritz N, Windholz L, Zaheer U, Farooq M, Arcimowicz B, Engleman Jr. R, Pickering JC, J¨ager H &
Guth¨ohrlein GH
Abstract:
We report the discovery of 23 new energy levels of even parity and 21 new energy levels of odd parity of the tantalum atom.
The results given here are based on investigations of the hyperfine structure of 221 new spectral lines of the tantalum atom
(Ta I) by means of laser spectroscopic methods, detecting laser-induced fluorescence. The excitation wavelengths were extracted
from high-resolution Fourier transform spectra
Copyright (2006) R Swedish Ac Sciences
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2005
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Hyperfine structure measurements of neutral manganese with Fourier transform spectroscopy
Blackwell-Whitehead RJ, Pickering JC, Pearse O, Nave G, Astrophysical Journal Suppl. Series 157 (2): 402-409 (2005)
(more info PDF)
Authors: Blackwell-Whitehead RJ, Pickering JC, Pearse O, Nave G
Abstract:
We report experimental hyperfine structure constants of levels in the neutral manganese atom, measured using Fourier transform
spectroscopy of hollow cathode discharges. In total, 208 spectral lines of astrophysical interest have been analyzed to obtain
hyperfine structure constants for 106 levels in Mn I, of which 67 have no previous hyperfine structure measurements.
The uncertainties in the magnetic dipole constants, A, are between 1 x 10-4 and 5 x 10-4 cm-1.
Hyperfine structure constants for an additional 18 levels compiled from the literature are also given.
Copyright (2005) AAS
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- Laboratory oscillator strength measurements for the spectrum of neutral manganese
Blackwell-Whitehead R, Xu HL, Pickering JC, Nave G, Lundberg H. MNRAS, 361, 1281 (2005)
(more info PDF)
Authors: Blackwell-Whitehead R, Xu HL, Pickering JC, Nave G, Lundberg H.
Abstract:
We report laboratory measurements of oscillator strengths for 44 transitions in the Mn I spectrum covering the wavelength
range 209-2780 nm. Nine energy level lifetimes have been measured using time resolved laser-induced fluorescence (LIF).
The lifetimes have been combined with branching fractions measured by Fourier transform spectroscopy to obtain absolute
oscillator strengths. In total, 24 of these oscillator strengths are measured for the first time, including transitions in
the previously unobserved infrared region above 2.0 micro m.
Copyright (2005) RAS
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2004
-
Atomic lines in infrared spectra for ultracool dwarfs
Y. Lyubchik, H.R.A. Jones, Y.V. Pavlenko, et al., A&A 416(2) pp. 655-659 (2004) (more info)
Authors: Y. Lyubchik, H.R.A. Jones, Y.V. Pavlenko, S. Viti, J.C. Pickering, R. Blackwell-Whitehead
Abstract: We provide a set of atomic lines which are suitable for the description of ultracool dwarf spectra from
10 000 to 25 000 Å. This atomic linelist was made using both synthetic spectra calculations and existing atlases of
infrared spectra of Arcturus and Sunspot umbra. We present plots which show the comparison of synthetic spectra and observed
Arcturus and Sunspot umbral spectra for all atomic lines likely to be observable in high resolution infrared spectra.
doi:10.1051/0004-6361:20034419 Copyright (2004)
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- Atomic lines in infrared spectra for ultracool dwarfs
N. Jaritz, G.H. Guthoehrlein, L. Windholz, et al., Physica Scripta 69 pp. 441-450 (2004) (more info)
Authors: N. Jaritz, G.H. Guthoehrlein, L. Windholz, D. Messnarz, R. Engleman, J.C. Pickering, H. Jaeger
Abstract: The hyperfine structures of 57 new spectral lines of the tantalum atom were investigated by means of laser
excitation. From the hyperfine patterns we have determined the angular momenta J, the magnetic hyperfine interaction constants
A and the electric quadrupole interaction constants B of 15 new energy levels of even parity and three new levels of odd parity.
The observation of laser-induced fluorescence led to the classification of further 156 spectral lines for the first time.
Additionally 92 lines, observed in high resolution Fourier transform spectra, were classified using a combination of their
wavenumbers and their characteristic hyperfine patterns.
doi:10.1238/Physica.Regular.069a00441 Copyright (2004)
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2003
-
High resolution photoabsorption cross section measurements of SO2 at 295 K between
220 and 325 nm
J.Rufus, G.Stark, P.L.Smith, et al., J. Geophys. Res.:Planets 108 (E2) art no. 5011 (2003) (more info)
Authors: J.Rufus, G.Stark, P.L.Smith, J.C.Pickering, A.P.Thorne
Abstract: High-resolution, ultraviolet SO2 photoabsorption cross
section data are required for modeling
density and temperature profiles of SO2 in solar system atmospheres. We report
measurements of such cross sections on SO2 at 295 K for the inline equation1B1 - inline
equation1A1 and C tilde1B2 - inline equation1A1 bands over the wavelength range 220 to 325 nm. Resolving powers of up to 550,000
were employed in order to study the congested spectrum of sharp SO2 features in parts of
this region. Our data are compared to earlier values obtained with lower resolving power.
doi:10.1029/2002JE001931 Copyright (2003)
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- High resolution absorption cross-section measurements of the Schumann-Runge bands of O2 by VUV Fourier transform spectroscopy
T. Matsui, A. S.-C. Cheung, K. W. S. Leung, et al., J. Molecular Spectroscopy 219 (1) pp. 45-57 (2003) (more info PDF)
Authors: T. Matsui, A. S.-C. Cheung, K. W. S. Leung, K. Yoshino, W. H. Parkinson, A. P. Thorne, J. E. Murray, K. Ito and T Imajo
Abstract: The photoabsorption spectrum of the O2 Schumann–Runge bands was
measured with resolution comparable to the Doppler widths by using the VUV Fourier transform spectrometer from Imperial College,
London, combined with synchrotron radiation as a continuum light source at the Photon Factory, KEK, Japan. The analysis of
the (12,0)–(17,0) bands of the Schumann–Runge system provides accurate rotational line positions as well as the line intensities
from 185 to 175 nm. Molecular constants of the v′=12 to 17 levels of the B3Σ-u state
have been determined. The (v′,0) band oscillator
strengths were determined as 2.38, 2.62, 2.70, 2.66, 2.40, and 2.12×10−5 for the bands from v′=12 to 17, respectively.
doi:10.1016/S0022-2852(03)00009-2 Copyright (2003) Elsevier
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- Investigation of the hyperfine structure of Ta I lines (VII)
D. Messnarz, N. Jaritz, B. Arcimowics, et al., Physica Scripta 68 (3) pp. 170-191 (2003) (more info)
Authors: D. Messnarz, N. Jaritz, B. Arcimowics, R. Engleman, J.C. Pickering, H. Jaeger, G.H. Guthoehrlein, L. Windholz, V.O. Zilio
Abstract: We have classified about 400 new spectral lines of neutral tantalum via laser excitation or observation of laser-induced fluorescence. 37 energy levels with even parity and seven levels with odd parity were found by means of systematic hyperfine structure investigations. For the new levels angular momentum, parity, magnetic hyperfine interaction constant A and electric quadrupole interaction constant B were deduced. In addition, we have classified 230 new lines observed in high resolution Fourier transform spectra by analysing their observed hyperfine structure patterns.
doi:10.1238/Physica.Regular.068a00170 Copyright (2003)
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- Extended term analysis of Mo II
H. Nilsson & J. C. Pickering, Physica Scripta 67 (3) pp. 223-233 (2003) (more info)
Authors:
Abstract: The spectrum of singly ionized molybdenum has been recorded with Fourier transform spectrometers in
the wavelength interval 1500–7000 Å. We report improved energy values for a total of 330 levels, 153 even and 177 odd,
which belong to the 4d5, 4d45s, 4d35s2, 4d46s, 4d45d,
4d45p and 4d35s5p configurations. 110 of the levels have been found in the present analysis.
We have also present calculated eigenvector components and oscillator strengths.
doi:10.1238/Physica.Regular.067a00223 Copyright (2003)
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- Application of a VUV Fourier transform spectrometer and synchrotron radiation source to measurements
of. VI. The epsilon(0,0) band of NO
A. S-C. Cheung, A. L. Wong, D. H-Y. Lo, et al., Journal of Chemical Physics 119(16) pp. 8373-8378 (2003) (more info)
Authors: A. S-C. Cheung, A. L. Wong, D. H-Y. Lo, K. W-S. Leung, K. Yoshino, A. P. Thorne and J. E. Murray, T. Imajo, K. Ito and T. Matsui
Abstract: The ϵ(0,0) (D2Σ+ –X2Πr) band of NO has been recorded
by using a vacuum ultraviolet Fourier transform spectrometer from Imperial College, London, with synchrotron radiation at the
Photon Factory, KEK, Japan, as a continuum light source. Analysis of the ϵ(0,0) band provides accurate rotational line
positions and term values as well as the photoabsorption cross sections. Molecular constants of the v = 0 level of the
D2Σ state have been determined as T0 = 53291.10 ± 0.10 cm-1, B0 = 1.99107±0.00005 cm-1 ,
and D0 = (6.6±0.1)×10−6 cm−1.
Accurate rotational line strengths have also been obtained and the sum of the line strengths for all rotational lines is
determined as 2.18×10−15 cm2 cm−1. The band oscillator strength of the ϵ(0,0) band is determined to be (2.47±0.12)×10−3.
Copyright (2003) American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in (Journal of Chemical Physics vol. 119 pages 8373-8378) and may be found at (http://jcp.aip.org/resource/1/jcpsa6/v119/i16/p8373_s1).
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2002
- High Resolution Fourier transform spectroscopy with the Imperial College UV FT spectrometer, and its applications to astrophysics and atmospheric physics: a review
J. C. Pickering, Vibrational Spectroscopy 29(1-2) pp. 27-43 (2002) (more info PDF)
Authors:
Abstract: The improvements in astronomical telescopes and their spectrographs, and in spectrographs used for studies
of the earth’s atmosphere have created a requirement for matching improvements in the laboratory atomic and molecular database needed
in the analysis of the astrophysical and atmospheric spectra. The technique of Fourier transform spectroscopy (FTS) is described and
its suitability in improving the atomic and molecular databases is discussed. The extension of the wavelength range of the Fourier
transform (FT) spectrometry into the vacuum ultraviolet to 140 nm is described. Examples are given of recent atomic and molecular
spectroscopy research using the Imperial College (IC) UV-FT spectrometer and applications to astrophysics and atmospheric physics
are given.
doi:10.1016/S0924-2031(01)00174-6 Copyright (2002) Elsevier
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- The FERRUM Project: Experimental oscillator strengths of the UV 8 multiplet and other UV transitions from the y6P levels of Fe II
J. C. Pickering, M. Donnelly, H. Nilsson, et al., A&A 396(2) pp. 715-722 (2002) (more info)
Authors: J. C. Pickering, M. Donnelly, H. Nilsson, A. Hibbert & S. Johansson
Abstract: We report on experimental branching fractions (BFs) for 19 transitions from the three 3d5 (6S)4s4p(3P) y6P levels in Fe II, measured in Fourier transform
spectra of a Penning discharge lamp and a hollow cathode lamp. The transition wavelengths span the interval between
1600 and 2850 Å. Absolute oscillator strengths ( f-values) have been derived by combining the BFs with experimental radiative
lifetimes recently reported in the literature. Theoretical f-values have been calculated using configuration interaction wavefunctions
. The new experimental and theoretical f-values are compared with data available in the literature and in databases.
The strongest lines measured belong to the UV 8 multiplet of Fe II, which has one ground state transition appearing as a prominent
feature at 1608 Å in interstellar spectra. The line is accompanied by a satellite at 1611 Å due to a level mixing, which is discussed
in the paper.
doi:10.1051/0004-6361:20021388 Copyright (2003)
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- Measurements of hyperfine structure in Ta II
V. Zilio & J. C. Pickering, MNRAS 334(1) pp. 48-52 (2002) (more info)
Authors: V. Zilio & J. C. Pickering
Abstract: We report the first extensive measurements of hyperfine structure in Ta II. Spectra of Ta II were recorded
by high-resolution Fourier transform spectrometry in the region 10000 – 53000 cm-1 (1886–10 000 Å) and the majority of
observed lines show significant hyperfine structure. Computer fits to several hundred of these line profiles have yielded values
of the magnetic dipole hyperfine interaction constant A for 88 energy levels with an uncertainty of between 0.5 and 10 per cent
for the majority of A factors. The A factors range from −0.078 to +0.065 cm-1
for the even levels and from −0.064 to +0.083 cm-1 for the odd levels. For the majority
of these A factors no previous measurements are known. Approximate values of the electric quadrupole hyperfine interaction constant
B were found for 73 levels. These measurements of A and B factors allow, for the first time, the effects of hyperfine structure
in Ta II lines to be correctly accounted for both in abundance analysis and in the resolution of blended lines in astrophysical spectra.
doi:10.1046/j.1365-8711.2002.05443.x Copyright (2002)
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- The FERRUM Project: New f-value data for Fe II and astrophysical applications
S.Johansson, A.Derkatch, M.Donnelly, et al., Physica Scripta T100 pp. 71-80 (2002) (more info)
Authors: S.Johansson, A.Derkatch, M.Donnelly, H.Hartman, A.Hibbert, H.Karlsson, M.Kock, Z.Li, D.S.Leckrone, U.Litzen, H.Lundberg, S.Mannervik, L-O.Norlin, H.Nilsson, J.C.Pickering, T.Rassen, D.Rostohar, P.Royen, A.Schmitt, M.Schultz-Johanning, C.M.Sikstrom, P.L.Smith, S.Svanberg, G.M.Wahlgren
Abstract: We present the FERRUM Project, an international collaboration aiming at a production and evaluation
of oscillator strengths (transition probabilities) of selected spectral lines of singly ionized iron group elements, that are of
astrophysical relevance. The results obtained include measurements and calculations of permitted and forbidden lines of Fe II.
The data have been applied to both emission and absorption lines in astrophysical spectra. We make comparisons between experimental,
theoretical and astrophysical f-values. We give a general review of the various measurements, and discuss the UV8 multiplet of Fe II
around 1610 Å in detail.
doi:10.1238/Physica.Topical.100a00071 Copyright (2002)
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- The application of a vacuum ultraviolet Fourier transform spectrometer and synchrotron radiation source to measurements of: V.
The beta(11,0) band of NO
J. Rufus, K. Yoshino, A. P. Thorne, et al., Journal of Chemical Physics 117(23) pp. 10621-10626 (2002) (more info PDF)
Authors: J. Rufus, K. Yoshino, A. P. Thorne, J. E. Murray, T. Imajo, K. Ito, T. Matsui
Abstract: The β(11,0) band of NO was measured at high resolution (0.06 cm-1 ) by
the vacuum ultraviolet Fourier transform spectrometer from Imperial College, London, using synchrotron radiation at the Photon
Factory, KEK, Japan, as a continuum light source. Such resolution facilitates a line by line analysis of the NO β(11,0) band which
yields accurate rotational line positions and term values as well as the photoabsorption cross sections. The molecular constants
of the B(11) 2Πr level are found to be T0 = 55983.203 ± 0.017 cm-1, A = 47.977±0.024, Bv = 1.01077 ± 0.00037 cm-1,
Dv = (6.7±0.8)×10-6 cm-1 and AD = 0.0438±0.0035 cm-1. The sum of the line strengths for all rotational transitions
of the NO β(11,0) band is determined as 3.04×10−16 cm2 cm-1, corresponding to a band oscillator strength of (3.44±0.21)×10-4.
Copyright (2002) American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in (Journal of Chemical Physics vol. 117 page 10621) and may be found at (http://jcp.aip.org/resource/1/jcpsa6/v117/i23/p10621_s1).
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- The application of a vacuum ultraviolet Fourier transform spectrometer and synchrotron radiation source to measurements of: IV.
The beta(6,0) and gamma(3,0) bands of NO
A. S. C. Cheung, D. H. Y. Lo, K. W. S. Leung, et al., Journal of Chemical Physics 116(1) pp. 155-161 (2002) (more info PDF)
Authors: A. S. C. Cheung, D. H. Y. Lo, K. W. S. Leung, K. Yoshino, A. P. Thorne, J. E. Murray, K. Ito, T. Matsui, T. Imajo
Abstract: The β(6,0) (B2 Πr –X2Πr )
and γ(3,0) (A2Σ+ – X 2Πr) bands of NO have been recorded
using a vacuum ultraviolet Fourier transform spectrometer with synchrotron radiation as light source. The analysis of the β(6,0) and γ(3,0) bands of NO provides accurate rotational line positions and term values. Molecular constants of the v = 6 level of the B2 Πr
and v = 3 level of the A2Σ+ have been determined.
Accurate rotational line strengths have also been obtained. The band oscillator strength
of the β(6,0) and γ(3,0) bands are determined to be 0.48×10−4 and 2.69×10−4, respectively.
Copyright (2002) American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in (Journal of Chemical Physics vol. 116 page 155) and may be found at (http://jcp.aip.org/resource/1/jcpsa6/v116/i1/p155_s1).
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2001
- New accurate data on the spectrum of neutral silver
J. C. Pickering, V. Zilio, Eur. Phys. J. D 13 pp. 181-185 (2001) (more info)
Authors: J. C. Pickering, V. Zilio
Abstract: High resolution spectra of neutral silver have been recorded by Fourier Transform Spectrometry in the
region 2000-8280 Å(50000 - 12000 cm-1) with silver-neon and silver-argon hollow cathode lamps as sources.
This work represents order-of-magnitude improvements, compared to previous work on Ag I, in accuracy of transition wavelengths
and wavenumbers, and energy level values. 35 classified Ag I transitions are given, and the wavenumber uncertainty for the strongest
lines is less than 0.002 cm-1. Improved values for 28 energy levels are presented.
doi:10.1007/s100530170264 Copyright (2001). The final publication is available at www.epj.org.
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- Oscillator strengths of UV transitions in Ti II
J. C. Pickering, A. P. Thorne, R. Perez, ApJ SS 132 pp. 403-409 (2001) (more info PDF)
Authors: J. C. Pickering, A. P. Thorne, R. Perez
Abstract: The relative intensities of 694 emission lines of Ti II between 187 and 602 nm from 89 levels have been measured by high-resolution Fourier transform spectrometry, using a hollow cathode lamp as light source. The spectral response function of the instrument was determined with calibrated tungsten halogen and deuterium lamps. Errors due to self-absorption in strong lines were eliminated by running the lamp at different currents. At least 95% of the predicted transition intensity has been measured for 83 of these levels, allowing reliable branching fractions to be found. The branching fractions have been combined with 39 measured and 44 computed lifetimes to give absolute transition probabilities for 624 lines. These agree well with the most recent values for 55 of the lines obtained in a similar way from seven of the measured lifetimes.
doi:10.1086/318958 Copyright (2001) The American Astronomical Society
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- The FERRUM Project: Branching ratios and atomic transition probabilities of Fe II transitions from the
3d6 (a3F)4p subconfiguration in the visible to VUV spectral region
J. C. Pickering, S. Johansson & P. L. Smith, A&A 377 pp. 361-367 (2001) (more info)
Authors: J. C. Pickering, S. Johansson & P. L. Smith
Abstract: We report measurements of the relative intensities of 81 emission lines of Fe II between 160 nm and 350 nm
(62168 cm-1 to 28564 cm-1) from 4 levels by high resolution Fourier transform spectrometry,
using a Penning discharge lamp as light source. These relative intensities have been used to determine the line branching fractions,
which have then been combined with accurate experimental radiative lifetime measurements reported recently to give absolute
transition probabilities and oscillator strengths for 81 lines. The accuracy of these f-values is compared with other previous
experimental measurements, and with theoretical values. The new transition probabilities will allow accurate determinations of Fe II
abundances in a wide variety of astrophysical objects.
doi:10.1051/0004-6361:20010943 Copyright (2001)
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- The application of a VUV Fourier transform spectrometer and synchrotron radiation source to measurements of: III. The
e (1,0) band of NO
J. Rufus, K. Yoshino, J. R. Esmond, et al., J. Chem. Phys. 115(8) pp. 3719-3723 (2001) (more info)
Authors: J. Rufus, K. Yoshino, J. R. Esmond, A. P. Thorne, J. E. Murray, T. Imajo, K. Ito and T. Matsui
Abstract: The ϵ(1,0) band of NO was measured at high resolution (0.06 cm−1) by the vacuum ultraviolet
(VUV) Fourier transform spectrometer from Imperial College, London, using synchrotron radiation at the Photon Factory, KEK, Japan,
as a continuum light source. Such resolution facilitates a line by line analysis of the NO ϵ(1,0) band which yields accurate
rotational line positions and term values as well as the photoabsorption cross sections. The molecular constants of the D(1) 2Σ level are found to be T0 = 55 570.582±0.055 cm−1, Bv = 1.979 66±0.000 19 cm−1, Dv = (5.8±4.7)×10−5cm−1, γ = −0.127±0.008 cm−1 and γD = −(1.03±0.04)×10−3 cm−1. The sum of
the line strengths for all rotational transitions of the NO ϵ(1,0) band is determined as
2.55×10−15 cm2 cm−1, corresponding to a band oscillator strength of 0.00288 ± 0.00017.
Copyright (2001) American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in (Journal of Chemical Physics vol. 115 page 3719) and may be found at (http://jcp.aip.org/resource/1/jcpsa6/v115/i8/p3719_s1).
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- Atomic and molecular spectroscopy with the Imperial College VUV high resolution Fourier transform spectrometer
in Fourier Transform Spectroscopy J. C. Pickering, A. P. Thorne, R. C. M. Learner, et al., OSA Technical Digest (Optical Society of America, Washington DC), pp. 5-6 (2001) (more info)
Authors: J. C. Pickering, A. P. Thorne, R. C. M. Learner, R. Blackwell
Abstract:
Copyright (2001)
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2000
- Precise Laboratory Wavelengths of importance to studies
of the time variation of the fine structure constant
Pickering JC, Thorne AP, LitzÉN, Webb JK, Zilio V, Monthly Notices of the Roy. Astron. Soc. 319, 163-167 (2000).
(more info PDF)
Authors: Pickering JC, Thorne AP, LitzÉN, Webb JK, Zilio V
Abstract: The quality of astronomical spectroscopic data now available is so high that interpretation
and analysis are often limited by the uncertainties of the laboratory data base. In particular,
the limit with which space±time variations in the fine structure constant a can be
constrained using quasar spectra depends on the availability of more accurate laboratory rest
wavelengths. We recently measured some transitions in magnesium by high-resolution
Fourier transform spectroscopy for this purpose, and we now report measurements on some
ultraviolet resonance lines of Zn II (2062 and 2026 Å), Cr II (2066, 2062 and 2056 Å ) and
Ni II (1751, 1741, 1709 and 1703 Å). Apart from the last line, which is very weak, the
uncertainty of these measurements is 0.002 cm-1 (0.08 mÅ ) for the lines around 2000 Å and
0.004 cm-1 (0.12mÅ) for the lines around 1700Å.
doi:10.1051/0004-6361:20010943 Copyright (2000) RAS
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Selected Publications: 2004 -1987
Selected Publications: 2004 - 1987
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