Iron-manganese-neon spectrum
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Sven Huldt
Henrik Hartman
Hampus Nilsson

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Atomic parameters

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 collisional parameters.
The fundamental entity in all diagnostic work is the spectral line – its position,
strength and profile and in the observed spectrum.

Position – Wavelength: Used for velocity measurements (Doppler shift). Extreme accuracy is needed in astrophysical applications.

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.)


Wavelengths

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.

Oscillator strengths (f-values)

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.

Hyperfine 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 (LIS).



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