Imperial College London

Imperial College Spectroscopy Laboratory

Recent Research Highlights




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

Posted: 10th May 2021


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

M. Ding & J.C. Pickering
Astrophysical Journal Suppl., 251 (2), 24 (2020)
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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.

Co2hfs
Observed (black) and fitted (red) line profile of a transition at 38289.969 cm-1 of Co II. The relative intensities of the hyperfine structure components and transition diagram are shown.



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

Posted: 30th April 2021

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
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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.

qua1
Artist’s impression of quasar J1120+0641, a very distant quasar - analysis of the line of sight absorption spectra to this quasar can give estimates of the fine structure constant as it was 13 billion years ago (Wilczynska et al, Science Advances 6 (17) 9672 (2020)). Credit: ESO/M. Kornmesser.



High Accuracy Stellar Spectroscopy

Posted: 15th April 2021

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
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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.

iau logo
IAU Website



Paper Published: Recent advances in experimental laboratory astrophysics

Posted: 15th October 2020

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
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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".

IAU1
Example of the impact of new accurate laboratory transition probabilities for the Gaia GES survey, tested in the Solar spectrum. The new atomic data is now in the Gaia GES linelist.



"Discovering Light" Workshop

Posted: 4th June 2018

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.

Festival1
Using their assembled spectrometers to look at lamp spectra



Special Session on Laboratory Astrophysics

Posted: 3rd June 2018

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.

EWASS/NAM 2018
EWASS logo



High Accuracy Stellar Spectroscopy

Posted: 31st May 2018

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.

iau logo
IAU Website



New Atomic Data For Stellar Composition

Posted: 25th May 2018

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)
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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.

Eta Carinae
Star Eta Carinae, Sc II has been observed (image from Wikipedia)



New Atomic Data for Hot Star Studies

Posted: 1st April 2016

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
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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.

Section of Co III spectrum, top: FTS, lower: grating
Short section of Co III spectrum
upper: FTS spectrum
lower: grating spectrum



New Atomic Data for Modelling Stellar Atmospheres

Posted: 24th September 2014

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.

EUV image of the Sun showing Fe emission
EUV image of the Sun showing
emission from iron atoms

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

Posted: 17th April 2014

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.

Gaia-ESO Survey
Gaia-ESO Survey Logo

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.

apj
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Copyright (2013) The American Astronomical Society.



Nature Editorial

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

Posted: 27th November 2013

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.

Nature Editorial
Nature Editorial

Atomic data for studies of star forming regions

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

Posted: 27th May 2013

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.

The Ring Nebula (M57)
The Ring Nebula (M57)

Last updated: 30th May 2018