A Catalog of 10,000 Very Metal-poor Stars from LAMOST DR3

Abstract

We present the result of a search for very metal-poor (VMP, ) stars in the Milky Way based on low-resolution spectra from Large sky Area Multi-Object fiber Spectroscopic Telescope (LAMOST) DR3, significantly enlarging the current candidate sample of these low-metallicity objects. The selection procedure results in a sample of 10,008 VMP stars covering a large area of sky in the Northern Hemisphere, and includes over 6800 targets brighter than V ∼ 16. This LAMOST DR3 VMP sample provides the largest number of VMP candidates to date that are sufficiently bright for follow-up high-resolution observation with 4–10 m telescopes, greatly expanding the VMP stars discovered in the northern sky, and can be used to balance the spatial distribution of VMP stars with high-resolution spectroscopic analyses. Comparison with stars having existing high-resolution analyses and Tycho Gaia Astrometric Solution parallaxes indicates that the derived stellar parameters and distance estimates are reliable. The sample reaches beyond 40 kpc in the halo, and contains over 670 candidates of extremely metal-poor ( ) and ultra-metal-poor ( ) stars. The distribution of V ϕ indicates that the sample consists of two halo components, with the retrograde component likely to be associated with the outer-halo population. A new criterion is proposed to select carbon-enhanced metal-poor (CEMP) star candidates, using line indices G1 and EGP over the range 4000 K < < 7000 K, resulting in 636 CEMP candidates from the LAMOST DR3 VMP sample.

Kinetic freeze-out in central heavy-ion collisions between 7.7 and 2760 GeV per nucleon pair

“…2 and Table 2) The general quality of the fits for all energies, particle species and the whole p t range is violated by the low p t pions at √ s N N = 2760 GeV where Monte Carlo underestimates the data (the first six p t bins were excluded from the fit in this case). Similar disagreement has been observed also in [17]. There are at least two effects, both included in our simulation, which help populate this p t region: pions originating from the resonance decays and the nonzero pion chemical potential ∼100 MeV.…”

Neutron star mergers and rare core-collapse supernovae as sources of r-process enrichment in simulated galaxies

“…The thin, dot-dashed line indicates a slope of unity, which is closely followed by the metallicity distribution function for subsolar metallicities. The distribution of metal-poor stars in our simulations, for which the number of stars decrease by an order of magnitude for every dex decrease in metallicity, is in agreement with some observational samples (Yong et al 2013;Li, Tan & Zhao 2018). However, other samples show a cutoff at low metallicity (Schörck et al 2009), potentially due to the way the sample was selected or differences in analysis of the data (Yong et al 2013).…”

The Pristine survey – X. A large population of low-metallicity stars permeates the Galactic disc

“…Together with the individual measurement uncertainties on the radial velocity derivation, these uncertainties are propagated in the derivation of the orbital parameters and their uncertainties. Li et al (2018) presented new metallicities for a set of 10,000 VMP star candidates from LAMOST DR3 (Zhao et al 2012;Cui et al 2012). We note there is a spurious effect in this VMP sample, where a lot of stars accumulate at the lower effective temperature limit of the employed model grid.…”

“…In general, the rarity of low-metallicity stars among the bulk of the more metal-rich MW stars has long limited the mapping of their distribution. However, recent, systematic, and large spectroscopic surveys (Allende Prieto et al 2014;Li et al 2018) or specific photometric surveys (Wolf et al 2018;Starkenburg et al 2017b) yield increasingly large spectroscopic samples of such stars. In this work, we use two well-known samples in order to study the orbital properties of the most metal-poor tail of disk stars.…”