TY - JOUR
T1 - The Pristine Survey IV
T2 - Approaching the Galactic metallicity floor with the discovery of an ultra metal-poor star
AU - Starkenburg, Else
AU - Aguado, David S.
AU - Bonifacio, Piercarlo
AU - Caffau, Elisabetta
AU - Jablonka, Pascale
AU - Lardo, Carmela
AU - Martin, Nicolas
AU - Sanchez-Janssen, Ruben
AU - Sestito, Federico
AU - Venn, Kim A.
AU - Youakim, Kris
AU - Prieto, Carlos Allende
AU - Arentsen, Anke
AU - Gentile, Marc
AU - Hernandez, Jonay I. Gonzalez
AU - Kielty, Collin
AU - Koppelman, Helmer H.
AU - Longeard, Nicolas
AU - Tolstoy, Eline
AU - Carlberg, Raymond G.
AU - Cote, Patrick
AU - Fouesneau, Morgan
AU - Hill, Vanessa
AU - McConnachie, Alan W.
AU - Navarro, Julio F.
N1 - Re-submitted to MNRAS after minor revisions
PY - 2018/7/11
Y1 - 2018/7/11
N2 - 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 alpha-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.
AB - 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 alpha-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.
KW - astro-ph.SR
KW - astro-ph.GA
U2 - 10.1093/mnras/sty2276
DO - 10.1093/mnras/sty2276
M3 - Article
SN - 0035-8711
JO - Monthly Notices of the Royal Astronomical Society (MNRAS)
JF - Monthly Notices of the Royal Astronomical Society (MNRAS)
ER -