Recent Research Highlights and News

The 13th International Conference on Atomic and Molecular Data and their applications (ICAMDATA13), Lanzhou, China, September 2024

Dr Milan Ding, Research Associate, in the Imperial College Spectroscopy Group described the latest research being undertaken in high resolution spectroscopy of heavy elements, lanthanides, giving background on motivation and applications of the new atomic data, and discussing the challenges and how these can be overcome in this research. We hope to be able to add here the link to listen to this talk when it is published.

Results from Dr Ding's ground breaking study of doubly ionised neodymium have recently been published. This collaborative project involved novel laboratory experiments in the Imperial College Spectroscopy Laboratory and challenging analysis of the resulting spectra to yield new atomic data, particularly atomic energy levels.
We collaborated with Dr Alexander Ryabtsev and Dr Tatiana Ryabchikova (Russian Academy of Sciences, Moscow), who carried out demanding atomic structure calculations to provide theoretical support for the study as well as the use of stellar spectra to provide additional confirmation of the new spectral line identifications from the laboratory measurements. The new atomic data is particularly important in applications in astronomy, ranging from understanding the origins of heavy elements to interpreting the light seen from colliding neutron stars, whose signals are being detected by gravitational waves.

Dr Ding's papers on new atomic data for heavy elements (doubly ionised neodymium) are published in Astronomy and Astrophysics Journal in two parts, with the first recently appearing:
Download PDF Copyright (2024) The Astronomy and Astrophysics Journal

New infra-red spectrometer

STFC Futures Grant awarded: "A New World Class Infrared Spectrometer for Fundamental Atomic Data for Astrophysics"

Our new infra-red - visible spectrometer (Bruker), funded by the STFC ( grant ST/X005100/1) now joins our visible-VUV spectrometer in our Spectroscopy Laboratory, broadening our access to high resolution spectra across a much wider wavelength range. The new infra red spectra we will observe will improve our measurement of key atomic data needed to interpret astronomical spectra from stars to quasars, exoplanets to colliding neutron stars.

Meet our PhD student Milan Ding, and build your own spectrometer

Imperial College outreach project in the White City area

Milan Ding

Learn more about what inspired PhD student Milan Ding to a PhD in laboratory astrophysics and atomic spectroscopy, and try your hand at building your own spectrometer.

Download the Looking at Light pack PDF Copyright (2023) Imperial College London and The Invention Rooms

Invited keynote talk at ASOS on Atomic Data Measured Using High Resolution Spectroscopy

The 14th International Colloquium on Atomic Spectra and Oscillator Strengths for Astrophysical and Laboratory Plasmas (ASOS14), Paris, July 2023

Dr Christian Clear, Research Fellow, in the Imperial Spectroscopy Group described the latest research being undertaken in the group, giving background on motivation and applications of our atomic data and recent highlights.

Dr Clear's keynote presentation slides PDF Copyright (2023) Imperial College London can be found at the ASOS14 conference website.

New Paper Published on Atomic Data For Ni II Allowing More Accurate Analyses of Astrophysical Spectra

Wavelengths and Energy Levels of Singly Ionized Nickel (Ni II) Measured Using Fourier Transform Spectroscopy

Christian P. Clear, Juliet C. Pickering, Gillian Nave, Peter Uylings & Ton Raassen
Astrophysical Journal Suppl., 261, 35 (2022)
Download PDF Copyright (2022) The American Astronomical Society

We have published new atomic data for wavelengths and atomic energy levels of singly ionised nickel, Ni II. Analyses of thousands of spectral lines of singly ionized nickel (Ni II) in nickel spectra measured by Fourier transform spectrometers in the region 1800–70,000 cm−1 (5555 – 143 nm) has led to a new understanding of the atomic energy levels in Ni II. This work has yielded at least an order of magnitude improvement in the accuracy of line wavelengths and energy levels compared with previously available data for Ni II. 283 previously known energy levels are improved, and 25 levels are found for the first time. Eigenvector compositions of the energy levels have been calculated using the Orthogonal Operator Method, and were an important aid in the analysis of the level structure. This research enables broader, more reliable and accurate application of Ni II data in astronomical chemical abundance analyses.

These new wavelength and atomic energy level data are important in ongoing studies of stellar spectra, in particular identification of Ni features and elemental chemical abundance determination.

This study is, to the best of our knowledge, the most accurate to date for Ni II wavelength and energy levels. The project continues with future publications in preparation on higher lying energy levels in Ni II and transition probabilities.

"Build Your Own Spectroscope" Workshop

Over 500 festival goers build their own spectroscopes in our Great Exhibition Road Festival Workshop, June 2022.

During the weekend of 18-19 June 2022 at the Great Exhibition Road Festival, our "Make your own spectroscope" Workshop provided both children and adults with the tools to make their own spectroscope: using just card and a CD!

At this workshop, four lamps each containing a different element were on display, but with their labels hidden, the elements in each lamp remained a mystery! Using their newly made spectroscopes, members of the public played detective and identified the neon, sodium, helium and cadmium in each lamp by comparing their observations with reference spectra. The unique "fingerprint" spectra of these lamps could be seen by the children using their own spectroscopes. Many people entered the prize draw, with the winner gaining a pocket diffraction grating spectroscope!

Paper Published on New Atomic Data For Hyperfine Structure of Co II for Accurate Stellar Abundances

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

M. Ding & J.C. Pickering
Astrophysical Journal Suppl., 251 (2), 24 (2020)
Download PDF Copyright (2020) The American Astronomical Society

We have published new atomic data for hyperfine structure of singly ionised cobalt, Co II. Analyses of hyperfine structure constants of singly ionized cobalt (Co II) were performed on cobalt spectra measured by Fourier transform spectrometers in the region 3000–63,000 cm−1 (3333 – 158.7 nm). Fits to over 700 spectral lines led to measurements of 292 magnetic dipole hyperfine interaction A constants, with typical uncertainties between ±0.4 mK and ±3.0 mK. 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.

These new hyperfine structure atomic data are important in ongoing studies of stellar spectra, in particular elemental chemical abundances. Cobalt is an iron group element, one of the odd-Z nuclei, where production of these elements in stars is less well understood. Hyperfine structure broadens spectral lines observed in stars, and if it is not understood, or measured in the laboratory it can lead to very significant errors in determining strengths of stellar spectral lines, which in turn leads to errors in the relative abundance of cobalt determined from these lines.

This study is, to the best of our knowledge, the most comprehensive of any iron group (3d) element in terms of new hyperfine structure splitting factors being found for the majority of known energy levels.

Paper Published on New Atomic Data for Quasar Studies of possible Time and Spatial Variations of the Fundamental Constants

Reference wavelengths of Si II, C II, Fe I, and Ni II for quasar absorption spectroscopy

Gillan Nave and Christian Clear,
Monthly Notices of the Royal Astonomical Society 502 (4), 5679-5685, April 2021
Download PDF of Published Paper
and PDF arxiv preprint
Download PDF Copyright (2021) Oxford University Press on behalf of Royal Astronomical Society.

Together with G. Nave at NIST we have published new atomic data for studies of quasars to investigate possible time variation of fundamental constants. Wavelengths of absorption lines in the spectra of galaxies along the line of sight to distant quasars can be used to probe the variability of the fine structure constant, α, at high redshifts, provided that the laboratory wavelengths are known to better than 6 parts in 10 ⁸ , corresponding to a radial velocity of ≈20 ms−1. For several lines of Si II, C II, Fe I, and Ni II, suitable for these studies, previously published wavelengths are inadequate for this purpose. Improved wavelengths for these lines were derived by analysing Fourier transform spectra. The accuracy of these lines has been improved by factors ranging from 2 to 10, and they can now be used to test variation of the fine structure constant.

High Accuracy Stellar Spectroscopy

Imperial College contributes to IAU Commission B5 Working Group on High Accuracy Stellar Spectroscopy Triennial Report

Paul Barklem, Sultana Nahar, Juliet Pickering, Norbert Przybilla, and Tatiana Ryabchikova
Website of High Accuracy Stellar Spectroscopy Triennial Report
Download PDF Copyright (2021) International Astronomical Union

As a member of the Working Group, High Accuracy Stellar Spectroscopy, of the IAU (International Astronomical Union), Juliet Pickering has contributed to the triennial report, highlighting recent advances in atomic data for stellar astrophysics applications.

Paper Published: Recent advances in experimental laboratory astrophysics

Recent advances in experimental laboratory astrophysics for stellar astrophysics applications and future data needs

Juliet C. Pickering , Maria Teresa Belmonte, Christian P. Clear, Florence Liggins and Florence Concepcion-Mairey
Proceedings of the International Astronomical Union, 15(S350) (Laboratory Astrophysics: from Observations to Interpretation Symposium) 220-228, 2019, F. Salama & H. Linnartz, eds. doi:10.1017/S1743921320000642
Download PDF Copyright (2020) International Astronomical Union

Our paper covers recent progress in new accurate atomic data for astrophysics applications, and looks to future atomic data needs for astrophysics. It is part of a volume published as a result of the successful IAU (International Astronomical Union) Symposium S350 "Laboratory Astrophysics: from Observations to Interpretation".

"Discovering Light" Workshop

Over 450 children take part in our Workshop at the Imperial Festival, April 2018

Over a busy weekend the Spectroscopy Team ran our "Discovering Light" workshop at the Imperial College Festival (28th-29th April 2018). Led by research associate, Dr Teruca Belmonte, the team, aided by researchers from other groups in the Physics department, helped over 450 children (aged 4-18) build their own spectrometers, and use these to investigate a range of mystery lamps. The unique "fingerprint" spectra of these lamps could be seen by the children. They discovered the spectra of leds, tungsten, sodium, and the room lights amongst others.

Special Session on Laboratory Astrophysics

EWASS/NAM special session, April 2018, Liverpool

Download PDF EWASS poster

We were part of the organizing committee for the Special Session: Atomic and molecular data needs for astronomy and astrophysics at EWASS (European Week of Astronomy and Space Science that was held with NAM (National Astronomy Meeting) in Liverpool, April 2018. Speakers from across Europe presented their research on theoretical and experimental atomic and molecular data for astrophysics, and data needs were highlighted by astronomers.

High Accuracy Stellar Spectroscopy

Imperial College contributes to IAU Commission B5 Working Group on High Accuracy Stellar Spectroscopy Triennial Report

Paul Barklem, Sultana Nahar, Juliet Pickering, Norbert Przybilla, and Tatiana Ryabchikova
Website of High Accuracy Stellar Spectroscopy Triennial Report
Download PDF Copyright (2018) International Astronomical Union

As a member of the Working Group, High Accuracy Stellar Spectroscopy, of the IAU (International Astronomical Union), Juliet Pickering has contributed to the triennial report, highlighting recent advances in atomic data for stellar astrophysics applications.

New Atomic Data For Stellar Composition

Lifetime measurements and oscillator strengths in singly ionized scandium and the solar abundance of scandium

A. Pehlivan Rhodin, M. T. Belmonte, L. Engstrom, et al
Monthly Notices Royal Astron. Soc 472, 3337–3353 (2017)
Download PDF Copyright (2017) Oxford University Press

We have published new atomic data for singly ionised scandium, Sc II as part of an international collaboration. New level lifetimes measured at the Lund High Power Laser Centre were combined with branching fractions obtained using spectra recorded by Fourier Transform Spectroscopy at Imperial College London to give new oscillator strengths (transition probabilities). These new oscillator strength atomic data are important in ongoing studies of stellar spectra, in particular elemental chemical abundances. Scandium is an iron group element, one of the odd-Z nuclei, where production of these elements in stars is less well understood. The transitions from highly excited levels that we studied give diagnostic value since they can be used to benchmark non-local thermodynamical equilibrium (NLTE) modelling of stellar atmospheres. A trustworthy NLTE treatment is the current challenge for accurate stellar abundances. High-precision atomic data for selected lines are important for this development. A new solar abundance for scandium is presented.

New Atomic Data for Hot Star Studies

The spectrum and term analysis of Co III measured using Fourier transform and grating spectroscopy

D. G. Smillie, J. C. Pickering, G. Nave, and P. L. Smith
Astrophysical Journal Supplement 223, 12 (11pp), March 2016
Download PDF Copyright (2016) The American Astronomical Society.

Together with collaborators at NIST we have published new atomic data for doubly ionised cobalt,Co III including accurate wavelengths (130-256 nm) and atomic energy levels. These new data are important in ongoing studies of Hot Star using the Hubble Space Telescope, particularly for the Advanced Spectral Library(ASTRAL) Treasury project, which is the stellar equivalent of the Hubble Deep Field. These hot stars shine brightly in the ultraviolet. By understanding the composition of hot stars we can understand stellar and galaxy evolution. Our new data, measured using Fourier Transform spectroscopy at Imperial College London and NIST gives at least order of magnitude improvement in accuracy for Co III.

New Atomic Data for Modelling Stellar Atmospheres

We have released a new set of Fe I transition probabilities which appear in the Astrophysical Journal Supplement Series. These new data will be used immediately by astronomers who are attempting to understand the composition of stars, and in particular will help them to accurately measure how much iron is present in the outer layers of stellar atmospheres. In total, we have provided new radiative lifetimes for 31 even-parity levels ranging from 45061 cm^-1 to 56842 cm^-1, and branching fractions for lines from 20 of these levels. By combining these data we then obtained 203 new transition probabilities of Fe I.

Atomic Data for the Gaia-ESO Survey (download pre-print PDF)

Our paper on experimentally measured experimental oscillator strengths appears in the Monthly Notices of the Royal Astronomical Society. In this paper, together with collaborators, we targeted the data requirements of the European Gaia-ESO Survey (GES), which 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. We report new data for 142 transitions of Fe I between 3526 Å and 10864 Å, many of which are urgently needed by GES, and assess the impact of these new data on solar spectral synthesis.

New IR atomic data for studies of Galactic evolution

Infrared Laboratory Oscillator Strengths of Fe I in the H-Band

Ruffoni MP, Allende Prieto C, Nave G, Pickering JC
Astrophysical Journal, 779 pp. 17 (2013)

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.

Nature Editorial

Nature Editorial on Laboratory Astrophysics (view on the Nature website)

Our recent paper on laboratory measured oscillator strengths for studies of Galactic evolution (M. P. Ruffoni et al., Astrophys. J. 779, 17; 2013) is featured in a Nature editorial on Laboratory Astrophysics. In this piece, the editors argue for greater funding of Laboratory Astrophysics in the future, and refer to our work as an example of studies that are needed in support of major astronomy and astrophysics projects. They also reiterate what we have observed previously: that "multimillion-dollar projects ... are producing data that cannot be analysed because of a failure to support much cheaper lab work on the ground". The full article is available on the Nature website.

Atomic data for studies of star forming regions

"Forbidden Lines" Revealed in Cobalt and Vanadium (download PDF)

The Astrophysical Journal Supplement Series has today accepted our latest paper for publication, in which we report accurate Ritz Wavelengths of Parity-Forbidden [Co II] and [V II] lines. These so-called "forbidden lines" arise from electronic transitions between metastable states of an atom and its ground state, and are not observed in high-density plasmas, such as in the atmospheres of stars. However, they are observed in other astronomical objects, including planetary nebulae and star-forming regions, and gas clouds around active galactic nuclei. These new results will therefore aid in the analysis of spectra from these objects.