An Optical Region Elemental Abundance Analysis of the HgMn Type Star HR 7775

Abstract

Optical region spectra of the chemically peculiar HgMn type star HR 7775 have been analyzed for the determination of elemental abundances and spectral line identification as a complementary study to the analysis of Hubble Space Telescope Goddard High Resolution Spectrograph spectra. The spectra were obtained with the SOFIN echelle spectrograph on the Nordic Optical Telescope at nominal resolving powers of R = 25,000, 80,000, and 170,000 and signal-to-noise ratios typically in excess of 100 : 1. The overall nature of the elemental abundance distribution is similar to other cool, HgMn stars; somewhat enhanced abundances for the iron-group elements, with progressively stronger enhancements for heavier elements. Of particular note are the presence of lines from the rare-earth spectra Nd III and Pr III, and the heavy elements Pt, Au, Hg, Tl, and Bi. The isotopic mixture for several lines of mercury and platinum has been investigated. For mercury a possible difference is found between the mixtures as derived from lines of Hg I and Hg II. Three lines of Pt II display the same mixture, which is different from that found from lower excitation lines at ultraviolet wavelengths. We present new laboratory Fourier Transform spectrometer measurements for isotopic and hyperfine structure components of Hg I λ4046 and 4358 and Hg II λ3984 A.