We study certain atomic parameters, important in diagnostics
of astrophysical and laboratory plasmas, and determine their
values directly or indirectly in laboratory measurements:
Wavelength, transition probability (oscillator strength),
radiative lifetime, energy levels, hyperfine constants (hfs),
and isotope shifts (IS), but we do not measure any
The fundamental entity in all diagnostic work is the spectral
line – its position, strength
and profile and in the observed
Position – Wavelength: Used for velocity
measurements (Doppler shift). Extreme accuracy is needed in
Strength – Transition probability or
Oscillator strength: Used in abundance analyses
Profile – hfs, IS: Necessary for detailed
abundance work, used for studies of stellar isotope compositions.
(Collisional parameters also affect the line profile.)
We measure and will measure wavelengths (or wavenumbers)
1. in the region 2000-6000 Å (50000-16000 cm-1)
with a Fourier-transform-spectrometer (FTS). It requires a
steady light source, e.g. a d.c. hollow-cathode lamp, which
means that we can normally investigate the three lowest ionization
stages of an element. The FTS has been operating for 15 years.
2. in the region 800-2000 Å with a VUV-echelle
spectrometer, where any kind of spectroscopic light source
could be used. It is supposed to operate in the fall of 2004.
3. in the near-IR region up to 5 µm with a
commercial IR-FTS instrument. It is supposed to operate in
the fall of 2004.
We derive absolute oscillator strengths (f-values) or transition
probabilities (A-values) of allowed (electric dipole) transitions
by combining experimental radiative lifetimes with branching
fractions. The lifetimes are measured at the Division of Atomic
Physics, LTH, often as LLC projects, and the branching fractions
are measured with our spectrometers.
We also derive transition probabilities for forbidden (magnetic
dipole and/or electric quadrupole) lines from experimental
radiative lifetimes of metastable states and theoretical or
astrophysical branching fractions. The lifetimes are measured
at the storage ring CRYRING, MSL, Stockholm, and the branching
fractions are determined from astrophysical spectra, as the
forbidden lines are not seen in laboratory spectra.
structure and isotope shifts
Many elements show hyperfine structure (hfs) in certain spectral
lines. In those cases, where the hfs is resolved in laboratory
FTS spectra we derive the hfs constants. Some elements also
show resolved isotope structure. In some cases we only report
the transition isotope shift (TIS), whereas in some others
we make a full analysis and derive the level isotope shifts