학술논문
GHOST Commissioning Science Results II: a very metal-poor star witnessing the early Galactic assembly
Document Type
Working Paper
Author
Sestito, Federico; Hayes, Christian R.; Venn, Kim A.; Jensen, Jaclyn; McConnachie, Alan W.; Pazder, John; Waller, Fletcher; Arentsen, Anke; Jablonka, Pascale; Martin, Nicolas F.; Matsuno, Tadafumi; Navarro, Julio F.; Starkenburg, Else; Vitali, Sara; Bassett, John; Berg, Trystyn A. M.; Diaz, Ruben; Edgar, Michael L.; Firpo, Veronica; Gomez-Jimenez, Manuel; Kalari, Venu; Lambert, Sam; Lawrence, Jon; Robertson, Gordon; Ruiz-Carmona, Roque; Salinas, Ricardo; Sebo, Kim M.; Venkatesan, Sudharshan
Source
Subject
Language
Abstract
This study focuses on Pristine$\_180956.78$$-$$294759.8$ (hereafter P180956, $[Fe/H] =-1.95\pm0.02$), a star selected from the Pristine Inner Galaxy Survey (PIGS), and followed-up with the recently commissioned Gemini High-resolution Optical SpecTrograph (GHOST) at the Gemini South telescope. The GHOST spectrograph's high efficiency in the blue spectral region ($3700-4800$~\AA) enables the detection of elemental tracers of early supernovae (\eg Al, Mn, Sr, Eu). The star exhibits chemical signatures resembling those found in ultra-faint dwarf systems, characterised by very low abundances of neutron-capture elements (Sr, Ba, Eu), which are uncommon among stars in the Milky Way halo. Our analysis suggests that P180956 bears the chemical imprints of a small number (2 or 4) of low-mass hypernovae ($\sim10-15 M_{\odot}$), which are needed to mostly reproduce the abundance pattern of the light-elements (\eg [Si, Ti/Mg, Ca] $\sim0.6$), and one fast-rotating intermediate-mass supernova ($\sim300\kms$, $\sim80-120 M_{\odot}$), which is the main channel contributing to the high [Sr/Ba] ($\sim +1.2$). The small pericentric ($\sim0.7$ kpc) and apocentric ($\sim13$ kpc) distances and its orbit confined to the plane ($\lesssim 2$ kpc), indicate that this star was likely accreted during the early Galactic assembly phase. Its chemo-dynamical properties suggest that P180956 formed in a system similar to an ultra-faint dwarf galaxy accreted either alone, as one of the low-mass building blocks of the proto-Galaxy, or as a satellite of Gaia-Sausage-Enceladus. The combination of Gemini's large aperture with GHOST's high efficiency and broad spectral coverage makes this new spectrograph one of the leading instruments for near-field cosmology investigations.
Comment: Accepted version, minor editing. New figure showing Sr and Ba lines. Section 4.7 revised
Comment: Accepted version, minor editing. New figure showing Sr and Ba lines. Section 4.7 revised