arXiv subjects

Juliet C. Pickering

Publications and source records attributed to Juliet C. Pickering.

6 recordsLinked to original sources

arXiv2026

Experimental Ni II Oscillator Strengths for Transitions from $3d^84d$ to $3d^84p$ Levels Measured Using High-resolution Fourier Transform Spectroscopy

We present the first experimentally measured oscillator strengths for Ni II 3d$^8$4d - 3d$^8$4p transitions. High-resolution Fourier transform spectra were recorded of Ni-He hollow cathode lamps, and intensity calibrated using deuterium standard lamps to determine relative intensities of Ni II emission lines between 200 and 395 nm. Branching fractions were determined for observed lines from 35 3d$^8$4d upper levels in total, and account for at least 95% of the predicted transition probability for 31 of these levels, with sufficient completeness to give reliable branching fractions. Combining our measured branching fractions with four experimental and 27 theoretically calculated energy level lifetimes provided absolute oscillator strengths for 174 lines, for which no previous experimental values exist. We compare the results with three sets of previously published theoretical calculations, illustrating the improvement of laboratory measurements for these atomic data. Please note: The transition probability datasets are withheld from this pre-print to ensure that only the peer-reviewed, definitive versions are released. This approach prevents the propagation of duplicate or inconsistent data across widely used atomic databases and modelling frameworks.

physics.atom-ph↗

arXiv2025

Wavelengths and Energy Levels of Neutral Manganese (Mn I) Determined Using High-Resolution Fourier Transform and Grating Spectroscopy

An extensive analysis of the spectrum of neutral manganese has been performed using spectra of manganese-neon and manganese-argon hollow cathode discharges measured using high resolution Fourier transform (FT) and grating spectroscopy over the range 151 - 5112 nm (1956 - 65876 cm-1). Wavelengths for 10426 spectral lines were extracted from the FT spectra, with uncertainties at least an order-of-magnitude lower than previous measurements. Wavelengths for 13397 lines from new grating spectra were determined for spectral regions beyond the FT spectra range or to provide wavelengths for weak transitions not observed in FT spectra. To aid in level identification, selected, previously published grating lines were included in the energy level optimisation, but no levels in this work relied solely on previously published wavelengths. In total, 24237 lines were included in the final spectral linelist, and these were used to identify 2186 Mn I transitions. These classified spectral lines were then used to optimise the values of 384 previously published energy levels of Mn I, with typical uncertainties of a few 10-3 cm-1, again typically an order-of-magnitude improvement in accuracy. Our study then expanded the known energy level structure of Mn I through the establishment of 18 new energy levels, reported here for the first time. In total, 2187 lines and 402 energy levels of Mn I have been determined as a result of our work, marking a substantial advance in the precision of Mn I atomic data which will enable far more accurate analyses of Mn I lines in astrophysical spectra. Please note: The final wavelength and energy level datasets are withheld from this pre-print to ensure that only the peer-reviewed, definitive versions are released. This approach prevents the propagation of duplicate or inconsistent data across widely used atomic databases and modelling frameworks.

physics.atom-ph↗

arXiv2023

The Spectrum and Energy Levels of the Low-lying Configurations of Nd III

Emission spectra of neodymium (Nd, Z=60) were recorded using Penning and hollow cathode discharge lamps in the region 11500-54000 cm$^{-1}$ (8695-1852 Å) by Fourier transform spectroscopy at resolving powers up to 106. Wavenumber measurements were accurate to a few 10$^{-3}$ cm$^{-1}$. Grating spectroscopy of Nd vacuum sliding sparks and stellar spectra were used to aid line and energy level identification. The classification of 433 transitions of doubly-ionised neodymium (Nd III) from the Penning lamp spectra resulted in the determination of 144 energy levels of the 4f$^4$, 4f$^3$5d, 4f$^3$6s, and 4f$^3$6p configurations of Nd III, 105 of which were experimentally established for the first time. Of the 40 previously published Nd III levels, 1 was revised and 39 were confirmed. New Nd III atomic structure calculations were made using the Cowan code parameterised by newly established levels. These results will not only benchmark and improve future semi-empirical atomic structure calculations of Nd III, but also enable more reliable astrophysical applications of Nd III, such as abundance analyses of kilonovae and chemically peculiar stars, and studies of pulsational wave propagation in these stars.

physics.atom-ph↗

arXiv2022

Comment on: "Hyperfine structure measurements of Co I and Co II with Fourier transform spectroscopy" by Fu et al. [JQSRT 2021, 107590]

This comment points out errors in the analysis of 61 magnetic hyperfine structure ($A$) constants of Co II energy levels by Fu et al. [JQSRT 2021, 107590]. The paper was published without full awareness of the extensive literature already available for Co II hyperfine $A$ constants at the time; 57 of 58 $A$ constants that were claimed to have been measured for the first time had already been measured by the prior work of Ding \& Pickering [ApJS 2020, 251:24], who had published $A$ constants for 292 levels of Co II. The $A$ constant of 3d$^6$4s$^2$ a$^5$D$_4$ has been determined by Fu et al. [JQSRT 2021, 107590] for the first time to be $12.0\pm1.8$ mK (1 mK $=$ 0.001 cm$^{-1}$), which was found to agree with line profiles observed by Ding \& Pickering [ApJS 2020, 251:24]. Discrepancies in 17 $A$ constants of Fu et al. [JQSRT 2021, 107590] were found, which are likely due to the analysis of weak, experimentally unclassified transitions with Ritz wavenumbers 25453.966 cm$^{-1}$ and 25149.948 cm$^{-1}$ by Fu et al. [JQSRT 2021, 107590] for the $A$ constants of the energy levels 3d$^7$($^2$G)4s a$^3$G$_5$ and 3d$^7$($^2$P)4s c$^3$P$_2$ respectively. Fewer transitions and poorer quality spectra analysed by Fu et al. [JQSRT 2021, 107590] are also concluded to have contributed to disagreements in the 17 $A$ constants.

physics.atom-ph↗

arXiv2020

Measurements of the Hyperfine Structure of Atomic Energy Levels in Co II

Analysis of hyperfine structure constants of singly ionised cobalt (Co II) were performed on cobalt spectra measured by Fourier transform spectrometers in the region $3000-63000$ cm$^{-1}$ ($3333-159$ nm). Fits to over $700$ spectral lines led to measurements of $292$ magnetic dipole hyperfine interaction $A$ constants, with values between $-32.5$ mK and $59.5$ mK ($1$ mK $=0.001$ cm$^{-1}$). Uncertainties of $255$ A constants were between $\pm0.4$ mK and $\pm3.0$ mK, the remaining $37$ ranged up to $\pm7$ mK. The electric quadrupole hyperfine interaction $B$ constant could be estimated for only $1$ energy level. The number of Co II levels with known $A$ values has now increased tenfold, improving and enabling the wider, more reliable and accurate application of Co II in astronomical chemical abundance analyses.

physics.atom-ph↗

arXiv2020

Atomic data for the Gaia-ESO Survey

We describe the atomic and molecular data that were used for the abundance analyses of FGK-type stars carried out within the Gaia-ESO Survey. We present an unprecedented effort to create a homogeneous line list, which was used by several abundance analysis groups to calculate synthetic spectra and equivalent widths. The atomic data are accompanied by quality indicators and detailed references to the sources. The atomic and molecular data are made publicly available in electronic form. In general experimental transition probabilities were preferred but theoretical values were also used. Astrophysical gf-values were avoided due to the model-dependence of such a procedure. For elements whose lines are significantly affected by hyperfine structure or isotopic splitting a concerted effort has been made to collate the necessary data for the individual line components. We also performed a detailed investigation of available data for line broadening due to collisions with neutral hydrogen atoms. Synthetic spectra calculated for the Sun and Arcturus were used to assess the blending properties of the lines. Among a subset of over 1300 lines of 35 elements in the wavelength ranges from 475 nm to 685 nm and from 850 nm to 895 nm we identified about 200 lines of 24 species which have accurate gf-values and are free of blends in the spectra of the Sun and Arcturus. For the broadening due to collisions with neutral hydrogen we recommend data based on Anstee-Barklem-O'Mara theory, where available, and to avoid lines of neutral species otherwise. Theoretical broadening data by R.L. Kurucz should be used for Sc II, Ti II, and Y II lines. For ionised rare-earth species the Unsöld approximation with an enhancement factor of 1.5 for the line width can be used. Desirable improvements in atomic data were identified for a number of species, including Al I, S I, Cr II, Na I, Si I, Ca II, and Ni I.

astro-ph.IM↗