Astronomy and Astrophysics, volume 450, 407-413 (2006/4-4)
Improved oscillator strengths and wavelengths in HfII, with applications to stellar elemental abundances.
LUNDQVIST M., NILSSON H., WAHLGREN G.M., LUNDBERG H., XU H.L., JANG Z.-K. and LECKRONE D.S.
Abstract (from CDS):
We present new and improved radiative lifetimes for eight levels in HfI and 18 levels in HfII, along with oscillator strengths and wavelengths for 195 transitions in HfII. With these data we determine the abundance of hafnium in two chemically peculiar stars: the hot-Am star HR 3383 and the HgMn star χ Lupi, and discuss the implications of the new data to the hafnium abundance for the Sun and the metal-poor galactic halo stars CS 22892-052 and CS 31082-001. The oscillator strengths are derived by combining radiative lifetimes measured with the laser induced fluorescence technique and branching fractions determined from intensity calibrated Fourier transform spectra. The hafnium abundance in the two sharp-lined peculair stars is determined by comparison of spectra obtained from instruments onboard the Hubble Space Telescope with synthetic spectra, while the abundance of hafnium in the solar photosphere and the metal-poor halo stars is discussed in terms of rescaling previous investigations using the new gf values. The abundance enhancement of hafnium has been determined in HR 3383 to be +1.7dex and that for χ Lupi A is +1.3dex. In the course of the analysis we have also determined an abundance enhancement for molybdenum in HR 3383 to be +1.2dex, which is similar to that known for χ Lupi A. The abundances in the metal-poor halo stars CS 31082-001 and CS 22892-052 were rescaled to log ε(Hf)=-0.75 and -0.82 respectively, with smaller 1σ uncertainty. This has the effect of improving the theoretical fits of r-process nucleosynthesis to abundance data for heavy elements. The change of gf values also implies that the hafnium abundance in the solar photosphere should be reduced by up to 0.2dex, thereby inducing a discrepancy with the meteoritic hafnium abundance.
atomic data - line: identification - stars: abundances