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 a-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 themostmetal-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.
The Pristine survey IV: Approaching the Galactic metallicity floor with the discovery of an ultra-metal-poor star / Starkenburg E.; Aguado D.S.; Bonifacio P.; Caffau E.; Jablonka P.; Lardo C.; Martin N.; Sanchez-Janssen R.; Sestito F.; Venn K.A.; Youakim K.; Prieto C.A.; Arentsen A.; Gentile M.; Hernandez J.I.G.; Kielty C.; Koppelman H.H.; Longeard N.; Tolstoy E.; Carlberg R.G.; Cote P.; Fouesneau M.; Hill V.; McConnachie A.W.; Navarro J.F.. - In: MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY. - ISSN 0035-8711. - STAMPA. - 481:3(2018), pp. 3838-3852. [10.1093/mnras/sty2276]
The Pristine survey IV: Approaching the Galactic metallicity floor with the discovery of an ultra-metal-poor star
Lardo C.Membro del Collaboration Group
;
2018
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 a-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 themostmetal-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.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
