HE 1327–2326, an Unevolved Star with [Fe/H] < –5.0. I. A Comprehensive Abundance Analysis

By Wak Aoki, A. Frebel, N. Christlieb, J. Norris, Timothy C. Beers, T. Minezaki, Paul Barklem, Satoshi Honda, M. Takada-Hidai, Martin Asplund and 10 more. 2005

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We present the elemental abundances of HE 1327-2326, the most iron-deficient star known, determined from a comprehensive analysis of spectra obtained with the Subaru Telescope High Dispersion Spectrograph. HE 1327-2326 is either in its main-sequence or subgiant phase of evolution. Its non-LTE-corrected iron abundance is [Fe/H] = -5.45, 0.2 dex lower than that of HE 0107-5240, the previously most iron-poor object known, and more than 1 dex lower than those of all other metal-poor stars. Both HE 1327-2326 and HE 0107-5240 exhibit extremely large overabundances of carbon ([C/Fe] ~ +4). The combination of extremely high carbon abundance with outstandingly low iron abundance in these objects clearly distinguishes them from other metal-poor stars. The large carbon excesses in these two stars are not the result of a selection effect. There also exist important differences between HE 1327-2326 and HE 0107-5240. While the former shows remarkable overabundances of the light elements (N, Na, Mg, and Al), the latter shows only relatively small excesses of N and Na. The neutron-capture element Sr is detected in HE 1327-2326, but not in HE 0107-5240; its Sr abundance is significantly higher than the upper limit for HE 0107-5240. The Li I λ6707 line, which is detected in most metal-poor dwarfs and warm subgiants having the same temperature as HE 1327-2326, is not found in this object. The upper limit of its Li abundance [log ϵ < 1.5] is clearly lower than the Spite plateau value. These data provide new constraints on models of nucleosynthesis processes in the first-generation objects that were responsible for metal enrichment at the earliest times. We discuss possible scenarios to explain the observed abundance patterns.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/4e86376ba3c698989fc6a91084c9f706524e0fef

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Citations in the corpus

The s-Process in Massive Stars at Low Metallicity: The Effect of Primary 14N from Fast Rotating Stars (2008, background): “The s process in fast rotating massive stars could provide a new scenario to explain the Sr enrichment coupled with high Sr/Ba observed in many stars (Truran et al. 2002; Aoki et al. 2005) at very low metallicity, including also the spread in the observed Sr/Ba ratio.”
THE MOST METAL-POOR STARS. II. CHEMICAL ABUNDANCES OF 190 METAL-POOR STARS INCLUDING 10 NEW STARS WITH [Fe/H] ⩽ −3.5,, (2012, background): “Meanwhile, parallel studies have started to identify a variety of chemically diverse objects(e.g., Aoki et al. 2005; Cohen et al. 2007; Lai et al. 2009), which may indicate that “we are beginning to see the anticipated and long sought stochastic effects of individual supernova events contributing…”
Evolution and nucleosynthesis of extremely metal-poor and metal-free low- and intermediate-mass stars - I. Stellar yield tables and the CEMPs (2008, background): “Goswami et al. 2006; Aoki et al. 2006a; Sivarani et al. 2006; alsosee Beers & Christlieb 2005 for an overview of the observations).”
Bright Metal-poor Stars from the Hamburg/ESO Survey. I. Selection and Follow-up Observations from 329 Fields (2006, background): “Subaru/HDS data were obtained and revealed it to be the new record holder for the most iron-poor star known to date, with [Fe/H] = −5.4 (Frebel et al. 2005, 2006; Aoki et al. 2006).”
A non-LTE study of neutral and singly-ionized calcium in late-type stars (2006, background): “The second point is connected with an extension of the metallicity range observed in stars down to [Fe/H] = −5.45 (Aoki et al. 2006).”
NUCLEOSYNTHESIS AND EVOLUTION OF MASSIVE METAL-FREE STARS (2008, methodology): “Here data are taken from Aoki et al. (2006) and Frebel et al. (2006) with new upper limits for Cr, Co, and Ni from Frebel et al. (2008).”
An absolutely calibrated T eff scale from the infrared flux method. Dwarfs and subgiants (2010, methodology): “We remark that there is no such thing as one Balmer lineTeff scale, but instead each study depends upon the adopted prescri - tions: LTE vs. NLTE, broadening recipes, mixing-length param- eter and even the details on how lines are fitted.”
HIGH-RESOLUTION SPECTROSCOPY OF EXTREMELY METAL-POOR STARS FROM SDSS/SEGUE. I. ATMOSPHERIC PARAMETERS AND CHEMICAL COMPOSITIONS (2012, methodology): “The chemical composition of this object was reported on by Aoki et al. (2006), using a high-resolution, high S/N spectrum.”
CARBON-ENHANCED METAL-POOR STAR FREQUENCIES IN THE GALAXY: CORRECTIONS FOR THE EFFECT OF EVOLUTIONARY STATUS ON CARBON ABUNDANCES (2014, unknown): “Individual references include: Allen et al. (2012), Akerman et al. (2004), Aoki et al. (2002, 2005, 2006, 2007, 2008, 2013), Barklem et al. (2005), Cohen et al. (2008, 2013), Cui et al. (2013), Goswami et al. (2006), Gratton et al. (2000), Hansen et al. (2011, 2014), Hollek et al. (2011, 2014), Ito…”
The s process: Nuclear physics, stellar models, and observations (2010, background): “At low metallicities, highresolution spectroscopic measurements of CEMP-s stars showed an even larger spread (Aoki et al., 2006a; Ivans et al., 2005; Roederer et al., 2008a; Sneden et al., 2008; Thompson et al., 2008).”
Very low-metallicity massive stars: - Pre-SN evolution models and primary nitrogen production (2006, background): “The two most metal-poor stars known to date: HE1327-2326 (Frebel et al. 2005; Aoki et al. 2006; Frebel et al. 2006) and HE 0107-5240 (Christlieb et al. 2004; Bessell et al. 2004) are both CEMP stars with a weak s-process enrichment.”