Ultraviolet Spectral Synthesis of Iota Herculis

TL;DR

This study demonstrates the effectiveness of LTE spectral synthesis in the UV for determining elemental abundances in the B-type star Iota Herculis, revealing new element data and assessing line list completeness.

Contribution

First application of LTE UV spectral synthesis to Iota Herculis, expanding elemental abundance data beyond visible spectra and evaluating line list and modeling limitations.

Findings

Abundances or upper limits for 24 elements derived.

Most results agree with previous studies.

Detected high abundance of two heavy elements, suggesting radiative levitation.

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. A high resolution spectrum of $\iota$~Herculis is available from 999 to 1400\,\AA.\ In this project, we investigate the abundance determination in the 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 VALD line list in this region, and the adequacy of LTE modeling in the UV for this star. We have used the LTE spectrum synthesis code {\sc zeeman} to model the UV spectrum of $\iota$~Herculis for elements with 5 $\le$ Z $\le$ 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. 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.