Revisiting the Iron Abundance in the Hyper Iron-poor Star HE 1327–2326 with UV COS/HAT Data
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Ezzeddine_2018_ApJ_863_168.pdf
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Author(s)
Ezzeddine, Rana
Frebel, Anna L.
Date Issued
August 2018
Journal
Astrophysical Journal
Publisher
American Astronomical Society
Citation
Ezzeddine, Rana and Anna Frebel. “Revisiting the Iron Abundance in the Hyper Iron-Poor Star HE 1327–2326 with UV COS/HST Data.” Astrophysical Journal 863, 2 (August 2018): 168 © 2018 American Astronomical Society
Version
Final published version
Abstract
We present a new iron abundance analysis of the hyper metal-poor star HE 1327-2326, based on Fe ii lines detected in its UV spectral range for the first time. In a Cosmic Origins Spectrograph (COS) spectrum, five new Fe ii lines could be measured. A Si i line was also detected for the first time. We determine a 1D local thermodynamic equilibrium (LTE) Fe ii abundance of [Fe ii/H] = -5.99 ±0.25. We also investigate departures from LTE for both Fe i and Fe ii lines. Guided by 3D non-LTE (NLTE) analyses of other well-studied metal-poor stars, we identify potential "residual" 3D effects in HE 1327-2326 arising from the absence of full 3D NLTE Fe calculations. Accordingly, we employ measurements of 10 weak Fe i lines previously detected in an optical spectrum of HE 1327-2326, as no Fe i lines are detectable in our UV spectrum. Following our previous work, we adopt the 1D NLTE Fe i abundance of = -5.20 ±0.12 for HE 1327-2326. Adopting a value based on the optical Fe i rather than UV lines was heavily informed by our extensive investigation of model atmosphere and radiative transfer effects on different lines across the entire UV-optical wavelength range. An iron abundance of [Fe/H] = -5.20 ±0.12 is only 0.2 dex higher than what was used in previous studies. Accordingly, no previous conclusions regarding the nature of the star are affected.
MIT Department
Massachusetts Institute of Technology. Department of Physics
MIT Kavli Institute for Astrophysics and Space Research
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DOI of Published Version
https://doi.org/10.3847/1538-4357/AAD3CB
