The bismuth abundance in the HgMn stars χ Lupi and HR 7775 and improved atomic data for selected transitions of BiI, BiII, and BiIII

High-resolution spectra of the chemically peculiar HgMn stars chi Lupi and HR 7775, obtained with the Hubble Space Telescope/Goddard High Resolution Spectrograph, are investigated for their abundance of bismuth by comparison with LTE synthetic spectrum modeling. HR 7775, previously known from International Ultraviolet Explorer spectra to display strong lines of Bi II, is determined to have bismuth present at an enhancement level of nearly 5 orders of magnitude from the lines Bi II lambda lambda 1436, 1902 and Bi III lambda 1423. The bismuth enhancement for chi Lupi is found to be near a level of 1.5 dex, and an ionization anomaly between Bi+ and Bi++ is apparent. HR 7775 abundance enhancements of the heavy elements platinum, [Pt/H] = 4.7 dex, and gold, [Au/H] = 3.8 dex, have also been determined. New laboratory measurements for wavelengths and hyperfine structure patterns of Bi I/Bi II/Bi III lines are presented, as well as the results of calculations for hyperfine structure constants and oscillator strengths for selected lines of Bi II and Bi III.