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2018ApJ...863..168E - Astrophys. J., 863, 168-168 (2018/August-3)

Revisiting the iron abundance in the hyper iron-poor star HE 1327-2326 with UV COS/HST data.

EZZEDDINE R. and FREBEL A.

Abstract (from CDS):

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 [Fe/H] = -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.

Abstract Copyright: © 2018. The American Astronomical Society. All rights reserved.

Journal keyword(s): line: formation - stars: abundances - stars: individual: HE 1327-2326 - stars: Population II

Simbad objects: 5

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2020.09.30-21:56:01

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