The Pristine survey IV: approaching the Galactic metallicity floor with the discovery of an ultra-metal-poor star. Issue 3 (18th August 2018)

• Record Type: Journal Article
• Authors: Starkenburg, Else; Aguado, David S; Bonifacio, Piercarlo; Caffau, Elisabetta; Jablonka, Pascale; Lardo, Carmela; Martin, Nicolas; Sánchez-Janssen, Rubén; Sestito, Federico; Venn, Kim A; Youakim, Kris; Allende Prieto, Carlos; Arentsen, Anke; Gentile, Marc; González Hernández, Jonay I; Kielty, Collin; Koppelman, Helmer H; Longeard, Nicolas; Tolstoy, Eline; Carlberg, Raymond G; Côté, Patrick; Fouesneau, Morgan; Hill, Vanessa; McConnachie, Alan W; Navarro, Julio F
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 481:Issue 3(2018)
• Page Start: 3838
• Page End: 3852
• Publication Date: 2018-08-18
• Subjects: stars: abundances -- Galaxy: abundances -- Galaxy: evolution -- Galaxy: formation -- Galaxy: halo; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/sty2276
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: The early Universe presented a star formation environment that was almost devoid of heavy elements. The lowest metallicity stars thus provide a unique window into the earliest Galactic stages, but are exceedingly rare and difficult to find. Here, we present the discovery of an ultra-metal-poor star, Pristine_221.8781+9.7844, using narrow-band Ca H&K photometry from the Pristine survey. Follow-up medium- and high-resolution spectroscopy confirms the ultra-metal-poor nature of Pristine_221.8781+9.7844 ([Fe/H] = −4.66 ± 0.13 in 1D LTE) with an enhancement of 0.3–0.4 dex in α-elements relative to Fe, and an unusually low carbon abundance. We derive an upper limit of A(C) = 5.6, well below typical A(C) values for such ultra-metal-poor stars. This makes Pristine_221.8781+9.7844 one of the most metal-poor stars; in fact, it is very similar to the most metal-poor star known (SDSS J102915+172927). The existence of a class of ultra-metal-poor stars with low(er) carbon abundances suggest that there must have been several formation channels in the early Universe through which long-lived, low-mass stars were formed.