Madeleine Burheim (Lund University): Experimental oscillator strengths for near-infrared astrophysical spectroscopy

Thursday 30 Nov 2023, 14:00 → 15:00 Europe/Stockholm

11134Å

Title: Experimental oscillator strengths for near-infrared astrophysical spectroscopy
Speaker: Madeleine Burheim 
Affiliation: Lund University
Time: Thursday 30 November 2023, 1400 to 1500
Location:  11134Å

 

Abstract: Since the invention of the CCD camera, astronomers have predominately explored the Universe through the visible spectrum. Consequently, focus has been put to exploring atomic transitions falling into this regime. Due to high amounts of interstellar extinction at optical wavelengths, the field of astrophysics is now turning to the near-IR wavelength regime, where the extinction is lower. Observing at these wavelengths allows us to pierce through dust clouds along the plane of our Galaxy and see into its very centre. This shift in focus, from the optical to the near-IR spectral ranges, means that the gaps in atomic data at these wavelengths need to be filled in, in order to reliably interpret and model the astrophysical spectra. Correctly interpreted stellar spectra allow for precise analyses of chemical abundances. Combined with an understanding of stellar structure and evolution, knowledge of stellar abundances makes it possible to study the chemical evolution and formation history of our Galaxy. The atomic transition parameter we aim to derive is the so-called oscillator strength (often referred to as f-value), which is a measure of the intrinsic strength of an atomic transition. Experimentally, the oscillator strength can be derived by combining branching fraction measurements with known radiative lifetimes of the upper energy levels. The branching fractions are measured by producing a plasma of the selected atomic species and recording the emitted light using a Fourier Transform Spectrometer. We have recently carried out studies on neutral aluminium, Al I, and singly ionized zirconium, Zr II. For aluminium we report log gf-values for 12 lines in the near-IR and optical spectral regions (670 – 4200 nm) and branching fractions for an additional 16 lines. The zirconium measurements include a set of completely new level energies and radiative lifetimes for 19 high lying even parity levels and improved energies for 15 odd parity levels, as well as log gf’s for 104 lines in the wavelength range 250 – 500 nm.