2001ApJ...547.1178W

We report laboratory measurements of the oscillator strengths for the Ti II vacuum ultraviolet resonance transitions 3d²4s a⁴F_3/2-3d4s4p(³P^o⁾ 4^F°_3/2 at λ_vac=191.0938 nm and 3d²4s a⁴F_3/2-3d4s4p(³P°) ⁴D°_1/2 at 191.0609 nm. Using the High Sensitivity Absorption Spectroscopy Experiment at the Synchrotron Radiation Center in Stoughton, Wisconsin, we determined the f-values for the Ti II 191.06 and 191.09 nm transitions relative to the well-known f-values of the Ti II resonance transitions 3d²4s a⁴F_3/2-3d²4p z⁴D°_3/2 at λ_vac=306.7245 nm and 3d²4s a⁴F_3/2-3d²4p z⁴G°_5/2 at 338.4740 nm. The Ti II 191.06 nm absorption f-value is 0.104±0.004. The Ti II 191.09 nm absorption f-value is 0.098±0.003. The Ti II 191.06 and Ti II 191.09 nm transitions have been detected in ground-based observations of high-redshift quasi-stellar object (QSO) absorption-line systems and in space-based observations. Use of these refined f-values causes a minimal change in the Ti abundances reported for some QSO absorption-line systems and for the Large Magellanic Cloud toward SN 1987A. The overabundance of Ti relative to Fe in comparison to solar abundances for two QSO absorption-line systems is decreased by our results. In general Ti abundances based on the 191 nm lines now can be put on an accurate absolute scale.