Ultraviolet spectral synthesis of Iota Herculis

Abstract

The atmospheric abundances of elements provide essential insights into the formation and evolution history of stars. The visible wavelength window has been used almost exclusively in the past to determine the abundances of chemical elements in B-type stars. However, some elements do not have useful spectral lines in the visible spectrum. A high-resolution spectrum of ι Herculis is available from 999 to 1400 Å. In this project, we investigate the chemicalabundance determination in the ultraviolet (UV). We identify the elements whose abundances can be tested, and search for elements whose abundances can be determined in the UV to add to those in the current literature. We also investigate the completeness of the Vienna Atomic Line Database line-list in this region, and the adequacy of local thermodynamic equilibrium (LTE) modelling in the UV for this star. We have used the LTE spectrum synthesis code ZEEMAN to model the UV spectrum of ι Herculis for elements with 5 ≤ Z ≤ 80. Abundances or upper limits are derived for 24 elements. We find that most of our results are in reasonable agreement with previous results. We estimate a value or an upper limit for the abundance of nine elements in this star that were not detected in the visible spectrum. LTE UV spectral synthesis is found to be a useful tool for abundance determination, even though limitations such as incomplete and uncertain atomic data, uncertain continuum normalization and scattered light, and severe blending can introduce difficulties. The high abundance of two heavy elements may be a sign of radiative levitation.