Transition probabilities of astrophysical interest in the niobium ions Nb$\mathsf{^+}$ and Nb$\mathsf{^{2+}}$

Abstract

Aims. We attempt to derive accurate transition probabilities for astrophysically interesting spectral lines of Nb ii and Nb iii and determine the niobium abundance in the Sun and metal-poor stars rich in neutron-capture elements.Methods. We used the time-resolved laser-induced fluorescence technique to measure radiative lifetimes in Nb ii. Branching fractions were measured from spectra recorded using Fourier transform spectroscopy. The radiative lifetimes and the branching fractions were combined yielding transition probabilities. In addition, we calculated lifetimes and transition probablities in Nb ii and Nb iii using a relativistic Hartree-Fock method that includes core polarization. Abundances of the sun and five metal-poor stars were derived using synthetic spectra calculated with the MOOG code, including hyperfine broadening of the lines.Results. We present laboratory measurements of 17 radiative lifetimes in Nb ii. By combining these lifetimes with branching fractions for lines depopulating the levels, we derive the transition probabilities of 107 Nb ii lines from 4d 3 5p configuration in the wavelength region 2240−4700 Å. For the first time, we present theoretical transition probabilities of 76 Nb III transitions with wavelengths in the range 1430−3140 Å. The derived solar photospheric niobium abundance log = 1.44 ± 0.06 is in agreement with the meteoritic value. The stellar Nb/Eu abundance ratio determined for five metal-poor stars confirms that the r-process is a dominant production method for the n-capture elements in these stars.

The elemental composition of the Sun

“…All useful Nb  lines are unfortunately strongly blended in the solar photospheric spectrum. We therefore choose to update the recent value obtained by Nilsson et al (2010), who derived the solar Nb abundance from spectral synthesis using the HM model. They used accurate new experimental g f -values and HFS data from Nilsson & Ivarsson (2008), supplemented by some of their own oscillator strengths.…”

Spectral investigation of doubly ionized rubidium (Rb III) from relativistic Hartree-Fock calculations

“…The present work can be seen as an extension of our recent investigations of the fifth row elements Y II, Y III [5], a e-mail: pascal.quinet@umons.ac.be Zr II [6], Nb I [7], Nb II, Nb III [8], Mo II [9][10][11], Tc II [12], Ru I [13], Ru II, Ru III [14], Rh II [15,16], Rh III [17], Pd I [18], Pd III [17], Ag II [19,20], Ag III [17], Sn I [21][22][23], Sb I [24], Te II and Te III [25].…”

Overview of recent advances performed in the study of atomic structures and radiative processes for the lowest ionization stages of heavy elements

“…For all these ions, the HFR + CPOL + CPEN method has been combined to a semi-empirical adjustment of radial parameters minimizing the differences between calculated energy levels and available experimental values to compute transition probabilities and oscillator strengths for a large number of spectral lines [69][70][71][72]. Because of the lack of radiative lifetime measurements, the quality of our calculations could only be estimated from isoelectronic comparisons, in particular from results we had formerly published in Nb II (isoelectronic of Mo III) [73], in Ru II (isoelectronic of Rh III) [74], and in Rh II (isoelectronic of Pd III) [75], for which similar HFR + CPOL + CPEN models revealed a very good agreement (generally within 10%) with accurate radiative lifetimes measured by means of the time-resolved laser-induced fluorescence technique. An accuracy of the same kind can thus be expected for the decay rates computed for the doubly charged ions considered in our new studies, at least for the most intense transitions.…”