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Motivation for our work
There is an overwhelming need for high quality atomic data for interpreting astronomical spectra.
Spectrometers onboard satellites (such as the Hubble Space Telescope,
Hinode) are used to detect the electromagnetic
radiation emitted
by stars. The
spectra that are obtained contain emission 'lines', which arise
when the atoms and ions present in the stellar atmosphere emit or absorb energy.
An understanding of these lines - their wavelengths and their intensities -
provides information on which elements are present in the stars and the relative
amounts of those elements. |
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In a new era of high resolution astrophysical
spectroscopy, vast quantities of data are being obtained and the
interpretation of observations is dependent on an ability to understand and
model these spectra. While some of these data can be obtained
experimentally, they are frequently of insufficient accuracy or limited to a
small number of transitions. Computational approaches are the only means by
which data of the required quality and quantity can be provided. The
calculation of highly accurate atomic physics data is essential to the field
of astrophysics.
The APARC group at Queen's University has long been at the forefront of
theoretical and computational advances in atomic structure, electron & photon collisions with atoms and ions.
At APARC we aim to provide high quality, reliable atomic data for use in
astronomy and astrophysics which will aid our understanding of the universe and thus help to answer
questions such as...What is the universe made of?
How do stars, galaxies and planets form and how do they evolve?
How does the sun affect the earth? |
Main Research Areas
Our work in APARC is currently concentrated into two areas:
Atomic data for the Fe-peak elements
Under this
theme we consider the calculation of atomic data pertaining to the astrophysically important Fe-peak elements
such as Fe II, Fe III, Fe IV, Fe V, Ni II, Ni III, Ni IV, Co II etc. Until recently, the accurate determination
of collision data for these ions remained one of the major outstanding problems in
atomic collision physics, because of the presence of an open 3d shell in the
description of the target ion. Recent theoretical and computational developments
and the availability of the national High Performance Computing facilities now
enable us to tackle these difficulties.
Atomic data facility supporting key observational efforts
This theme focuses on the collision and structure data imperative
for the interpretation of data from key ongoing or planned observational
missions. Astronomers and astrophysicists using state-of-the-art research
facilities are generating huge amounts of spectral data at a very high rate. To
simulate these observations, sophisticated modelling codes are being employed.
However, this entire observational effort relies ultimately on another
'facility' the atomic data facility for the evaluation of accurate data which
are vital input to the modelling codes.
Data Production
We produce a variety of data including oscillator strengths
(or equivalently A-values),
electron-impact excitation cross sections, collision strengths and the
maxwellian average effective collision strengths, as well as photoionization
cross sections.
To facilitate the study of atomic structure and collision processes we use
several powerful computer codes.
Atomic structure calculations are carried out using CIV3 and GRASP.
The CIV3 code was developed by a member of our research group (Prof Hibbert)
whilst another member of our group (Dr Norrington) was a key member of the team that developed the relativistic
structure code GRASP.
Collision and photoionization calculations are carried out by codes based on
the R-matrix method. The use of R-matrix theory in atomic and molecular processes has been
pioneered by a member of our group (Prof Burke), resulting in the development of
a set of robust computer programs capable of tackling the type of calculations
considered by the group. A range of R-matrix based codes are used including
RMATRX1, the Dirac Atomic R-matrix
codes (DARC) and the parallel R-matrix suite, RMATRXII and PFARM. Further
theoretical and computational developments have made RMATRXII and PFARM invaluable codes for the electron collision
studies. These codes are very powerful software tools which facilitate the study
of atomic structure and collision processes and, when used by experienced
theoreticians, are capable of yielding high quality atomic data.
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