EGAS41 - Swansea University

41 st EGAS CP 125 Gdańsk 2009
Transition probabilities of astrophysical interest in Niobium
ions (Nb II and Nb III)
H. Nilsson 1 , H. Hartman 1 , L. Engström 2 , H. Lundberg 2 , C. Sneden 3 , V. Fivet 4 ,
P. Palmeri 4 , P. Quinet 4,5 , É. Biémont4,5
1 Lund Observatory, Lund University,
PO Box 43, SE-221 00 Lund, Sweden
2 Department of Physics, Lund Institute of Technology, PO Box 118, SE-221 00 Lund, Sweden
3 Department of Astronomy and McDonald Observatory,
University of Texas, Austin, TX 78712, USA
4 Astrophysique et Spectroscopie, Université de Mons-Hainaut, B-7000 Mons, Belgium
5 IPNAS, Université de Liège, Sart Tilman, B-4000 Liège, Belgium
∗ Corresponding author: P. Quinet@umh.ac.be,
About half of the stable nuclei heavier than iron are believed to be synthesized through a
slow s-process in the late stages of the evolution of stars with masses in the approximate
range 0.8 - 8 M Sun . This process occurs when the star is in the AGB phase of its life. A
few s-process elements are particularly interesting because, along with giving a clue for
the mere operation of the s-process, they provide information on the time scales involved.
These elements are technetium, niobium and ruthenium.
In the present work, we have obtained a new set of accurate transition probabilities
in niobium ions (Nb + and Nb 2+ ) for selected transitions of astrophysical interest.
To our knowledge, no transition probabilities or radiative lifetimes at all are available
so far for Nb 2+ . Experimental or theoretical transition probabilities in the spectrum of
Nb II are very scarce. The most recent experimental work in Nb II is due to Nilsson
& Ivarsson [1] who were able to measure branching fractions (BF) of 145 lines in the
wavelength interval 260 - 460 nm and to deduce hyperfine splitting constants for 28 even
and 24 odd levels.
In the present work, 17 lifetimes of Nb + have been measured with the time-resolved
laser-induced fluorescence technique [2] and the results compared to HFR calculations
including core-polarization effects [3,4]. New BFs have been also obtained with highresolution
Fourier transform spectroscopy.
A particularly good agreement is observed between theory and experiment and this
agreement gives considerable weight to the new set of oscillator strengths obtained for 109
transitions of Nb II in the range 259-392 nm. Transition probabilities are also proposed,
for the first time, for 76 Nb III transitions with wavelengths in the range 143 - 315 nm.
Application of the new results to the determination of the chemical composition of the
sun and some r-process-rich very metal-poor stars will be discussed.
The present results will be published in A & A.
References
[1] H. Nilsson, S. Ivarsson, A&A 492, 609 (2008)
[2] H. Nilsson, L. Engström, H. Lundberg, P. Palmeri, V. Fivet, P. Quinet, É. Biémont,
Eur. Phys. J. D 549, 13 (2008)
[3] R.D. Cowan The Theory of Atomic Structure and Spectra, Berkeley, CA: University of
California Press (1981)
[4] P. Quinet, P. Palmeri, É. Biémont, M.M. McCurdy, G. Rieger, E.H. Pinnington, M.E.
Wickliffe, J.E. Lawler, MNRAS 308, 934 (1999)
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