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S. Ivarsson, G.M. Wahlgren, H.-G. Ludwig (Lund Observatory)
New atomic data (Ivarsson et al. 2001, Physica Scripta 64, 455) have opened the possibility of re-evaluating the solar photospheric abundance of the rare-earth element praseodymium. The experimental spectra were recorded in the region 2000 to 7000 Å with the Lund UV Fourier transform spectrometer and a hollow-cathode light source. These data allowed us to measure accurate wavelengths, re-analyse energy levels and determine the hyperfine structure for transitions of Pr II and Pr III. In addition, energy level lifetimes were measured at the Lund Laser Centre, which combined with the new experimental branching fractions lead to revisions of the gf values for many lines. The abundance of Pr in the solar photosphere was determined from synthetic spectrum fitting of three Pr II lines found in high-resolution solar observations from Kitt-Peak (NOAO) and Junfraujoch observatories. The 1D modelling was accomplished using the ATLAS/SYNTHE LTE codes (Kurucz 1998) and resulted in a Pr abundance (log \epsilon =0.40±0.1) that represents a significant lowering from the current canonical value of the solar photospheric abundance (log \epsilon =0.71±0.08, Biemont et al. 1979, Sol. Phys. 61, 17). We also tested the influence of 3D effects on the determination of the Pr abundance using the CO5BOLD radiation-hydrodynamics code (Freytag et al. 2002, AN 323, 213). Our preliminary results show insignificant differences in the equivalent widths of the Pr II lines between the 3D and 1D cases. Our new solar abundance of Pr differs from that determined from a sample of two carbonaceous condrite meteorites (log \epsilon=0.78±0.03, Lodder 2003, ApJ 591, 1220) and raises such questions as the appropriateness of assuming the convergence of solar and meteoritic abundances and the accuracy of modelling the solar spectrum.
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Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.