TY - JOUR
T1 - The Pristine survey – XIV. Chemical analysis of two ultra-metal-poor stars
AU - Lardo, C.
AU - Mashonkina, L.
AU - Jablonka, P.
AU - Bonifacio, P.
AU - Caffau, E.
AU - Aguado, D. S.
AU - González Hernández, J. I.
AU - Sestito, F.
AU - Kielty, C. L.
AU - Venn, K. A.
AU - Hill, V.
AU - Starkenburg, E.
AU - Martin, N. F.
AU - Sitnova, T.
AU - Arentsen, A.
AU - Carlberg, R. G.
AU - Navarro, J. F.
AU - Kordopatis, G.
PY - 2021/12
Y1 - 2021/12
N2 - Elemental abundances of the most metal-poor stars reflect the conditions in the early Galaxy and the properties of the first stars. We present a spectroscopic follow-up of two ultra-metal-poor stars ([Fe/H] < -4.0) identified by the survey Pristine: Pristine 221.8781+9.7844 and Pristine 237.8588+12.5660 (hereafter Pr 221 and Pr 237, respectively). Combining data with earlier observations, we find a radial velocity of -149.25 ± 0.27 and -3.18 ± 0.19 km s-1 for Pr 221 and Pr 237, respectively, with no evidence of variability between 2018 and 2020. From a one-dimensional (1D) local thermodynamic equilibrium (LTE) analysis, we measure [Fe/H]LTE = -4.79 ± 0.14 for Pr 221 and -4.22 ± 0.12 for Pr 237, in good agreement with previous studies. Abundances of Li, Na, Mg, Al, Si, Ca, Ti, Fe, and Sr were derived based on the non-LTE (NLTE) line formation calculations. When NLTE effects are included, we measure slightly higher metallicities: [Fe/H]NLTE = -4.40 ± 0.13 and -3.93 ± 0.12, for Pr 221 and Pr 237, respectively. Analysis of the G band yields [C/Fe]1D-LTE ≤ +2.3 and [C/Fe]1D-LTE ≤ +2.0 for Pr 221 and Pr 237. Both stars belong to the low-carbon band. Upper limits on nitrogen abundances are also derived. Abundances for other elements exhibit good agreement with those of stars with similar parameters. Finally, to get insight into the properties of their progenitors, we compare NLTE abundances to theoretical yields of zero-metallicity supernovae (SNe). This suggests that the SNe progenitors had masses ranging from 10.6 to 14.4 M⊙ and low-energy explosions with (0.3-1.2) × 1051 erg.
AB - Elemental abundances of the most metal-poor stars reflect the conditions in the early Galaxy and the properties of the first stars. We present a spectroscopic follow-up of two ultra-metal-poor stars ([Fe/H] < -4.0) identified by the survey Pristine: Pristine 221.8781+9.7844 and Pristine 237.8588+12.5660 (hereafter Pr 221 and Pr 237, respectively). Combining data with earlier observations, we find a radial velocity of -149.25 ± 0.27 and -3.18 ± 0.19 km s-1 for Pr 221 and Pr 237, respectively, with no evidence of variability between 2018 and 2020. From a one-dimensional (1D) local thermodynamic equilibrium (LTE) analysis, we measure [Fe/H]LTE = -4.79 ± 0.14 for Pr 221 and -4.22 ± 0.12 for Pr 237, in good agreement with previous studies. Abundances of Li, Na, Mg, Al, Si, Ca, Ti, Fe, and Sr were derived based on the non-LTE (NLTE) line formation calculations. When NLTE effects are included, we measure slightly higher metallicities: [Fe/H]NLTE = -4.40 ± 0.13 and -3.93 ± 0.12, for Pr 221 and Pr 237, respectively. Analysis of the G band yields [C/Fe]1D-LTE ≤ +2.3 and [C/Fe]1D-LTE ≤ +2.0 for Pr 221 and Pr 237. Both stars belong to the low-carbon band. Upper limits on nitrogen abundances are also derived. Abundances for other elements exhibit good agreement with those of stars with similar parameters. Finally, to get insight into the properties of their progenitors, we compare NLTE abundances to theoretical yields of zero-metallicity supernovae (SNe). This suggests that the SNe progenitors had masses ranging from 10.6 to 14.4 M⊙ and low-energy explosions with (0.3-1.2) × 1051 erg.
KW - stars: abundances
KW - Galaxy: abundances
KW - Galaxy: evolution
KW - Galaxy: formation
KW - Galaxy: halo
KW - Astrophysics - Solar and Stellar Astrophysics
KW - Astrophysics - Astrophysics of Galaxies
U2 - 10.1093/mnras/stab2847
DO - 10.1093/mnras/stab2847
M3 - Article
SN - 0035-8711
VL - 508
SP - 3068
EP - 3083
JO - Monthly Notices of the Royal Astronomical Society
JF - Monthly Notices of the Royal Astronomical Society
IS - 2
ER -