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BRIGHT METAL-POOR STARS FROM THE HAMBURG/ESO SURVEY. II. A CHEMODYNAMICAL ANALYSIS
Beers, Timothy C.,Placco, Vinicius M.,Carollo, Daniela,Rossi, Silvia,Lee, Young Sun,Frebel, Anna,Norris, John E.,Dietz, Sarah,Masseron, Thomas American Astronomical Society 2017 The Astrophysical journal Vol.835 No.1
<P>We obtain estimates of stellar atmospheric parameters for a previously published sample of 1777 relatively bright (9 < B < 14) metal-poor candidates from the Hamburg/ESO Survey. The original Frebel et al. analysis of these stars was able to derive estimates of [Fe/H] and [C/Fe] only for a subset of the sample, due to limitations in the methodology then available. A new spectroscopic analysis pipeline has been used to obtain estimates of T-eff, log g, [Fe/H], and [C/Fe] for almost the entire data set. This sample is very local-about 90% of the stars are located within 0.5 kpc of the Sun. We consider the chemodynamical properties of these stars in concert with a similarly local sample of stars from a recent analysis of the Bidelman and MacConnell 'weak metal' candidates by Beers et al. We use this combined sample to identify possible members of the halo stream of stars suggested by Helmi et al. and Chiba & Beers, as well as stars that may be associated with stripped debris from the putative parent dwarf of the globular cluster Omega Centauri, suggested to exist by previous authors. We identify a clear increase in the cumulative frequency of carbon-enhanced metal-poor (CEMP) stars with declining metallicity, as well as an increase in the fraction of CEMP stars with distance from the Galactic plane, consistent with previous results. We also identify a relatively large number of CEMP stars with kinematics consistent with the metal-weak thick-disk population, with possible implications for its origin.</P>
THE CHEMICAL COMPOSITIONS OF VERY METAL-POOR STARS HD 122563 AND HD 140283: A VIEW FROM THE INFRARED
Afş,ar, Melike,Sneden, Christopher,Frebel, Anna,Kim, Hwihyun,Mace, Gregory N.,Kaplan, Kyle F.,Lee, Hye-In,Oh, Heeyoung,Oh, Jae Sok,Pak, Soojong,Park, Chan,Pavel, Michael D.,Yuk, In-Soo,Jaffe, Dan American Astronomical Society 2016 The Astrophysical journal Vol.819 No.2
<P>From high resolution (R similar or equal to 45,000), high signal-to-noise ratio (S/N > 400) spectra gathered with the Immersion Grating Infrared Spectrograph (IGRINS) in the H and K photometric bands, we have derived elemental abundances of two bright, well-known metal-poor halo stars: the red giant HD 122563 and the subgiant HD 140283. Since these stars have metallicities approaching [Fe/H] = -3, their absorption features are generally very weak. Neutral-species lines of Mg, Si, S and Ca are detectable, as well as those of the light odd-Z elements Na and Al. The derived IR-based abundances agree with those obtained from optical-wavelength spectra. For Mg and Si the abundances from the infrared transitions are improvements to those derived from shorter wavelength data. Many useful OH and CO lines can be detected in the IGRINS HD 122563 spectrum, from which derived O and C abundances are consistent to those obtained from the traditional [O I] and CH features. IGRINS high resolutions Hand K-band spectroscopy offers promising ways to determine more reliable abundances for additional metal-poor stars whose optical features are either not detectable, or too weak, or are based on lines with analytical difficulties.</P>