Imperial College London

Imperial College Spectroscopy Laboratory


Recent Research Highlights

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"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, 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.

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 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
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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.

Download PDF

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