Metal-poor Stars Observed with the Automated Planet Finder Telescope. I. Discovery of Five Carbon-enhanced Metal-poor Stars from LAMOST

Abstract

We report on the discovery of five carbon-enhanced metal-poor (CEMP) stars in the metallicity range of −3.3 < [Fe/H] < −2.4. These stars were selected from the LAMOST DR3 low-resolution (R∼ 2,000) spectroscopic database as metal-poor candidates and followed-up with high-resolution spectroscopy (R∼110,000) with the LICK/APF. Stellar parameters and individual abundances for 25 chemical elements (from Li to Eu) are presented for the first time. These stars exhibit chemical abundance patterns that are similar to those reported in other literature studies of very and extremely metal-poor stars. One of our targets, J2114−0616, shows high enhancement in carbon ([C/Fe]=1.37), nitrogen ([N/Fe]= 1.88), barium ([Ba/Fe]=1.00), and europium ([Eu/Fe]=0.84). Such chemical abundance pattern suggests that J2114−0616 can be classified as CEMP-r/s star. In addition, the star J1054+0528 can be classified as a CEMP-rI star, with [Eu/Fe]=0.44 and [Ba/Fe]=−0.52. The other stars in our sample show no enhancements in neutron-capture elements and can be classified as CEMP-no stars. We also performed a kinematic and dynamical analysis of the sample stars based on Gaia DR2 data. The kinematic parameters, orbits, and binding energy of these stars, show that J2114−0616 is member of the outer halo population, while the remaining stars belong to the inner halo population but with an accreted origin. Collectively, these results add important constraints on the origin and evolution of CEMP stars as well as on their possible formation scenarios.

The Pristine survey – IX. CFHT ESPaDOnS spectroscopic analysis of 115 bright metal-poor candidate stars

“…Stars in the nearby dwarf galaxies typically have lower abundances of αand odd-Z elements, attributed to their slower star formation histories and/or fewer number of high mass stars overall (Venn et al 2004;Tolstoy et al 2009;Nissen & Schuster 2010;McWilliam et al 2013;Frebel & Norris 2015;Hayes et al 2018), while significant variations in heavy r-process elements in some dwarf galaxies, and globular clusters, are discussed in terms of contributions from individual compact binary merger events, like GW170817 (e.g., Roederer 2011;Roederer et al 2018a;Ji et al 2016Ji et al , 2019. In addition, about a third of the [Fe/H] < −2.5 stars 1 in the Galactic halo show very high enhancements in carbon (the carbon-enhanced metal-poor stars, "CEMP"; Yong et al 2013;Aguado et al 2019a also see Kielty et al 2017;Mardini et al 2019), discussed as a signature of the earliest chemical enrichment in the Universe. However, at least one ultra metal-poor star is not carbonenhanced (SDSS J102915+172927, Caffau et al 2012), and the known metal-poor stars in the Galactic bulge do not show carbon-enhancements (Howes et al 2016;Lamb et al 2017).…”

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The regular dynamics through the finite‐time Lyapunov exponent distributions in 3D Hamiltonian systems

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