J/MNRAS/546/G170 Metal-poor stars with X-Shooter (Lowe+, 2026)
Detailed abundance determination of metal-poor stars with X-Shooter.
I. Unusual chemistry in halo stars
Lowe B.D.C., Nordlander T., Casagrande T., Da Costa G.S., Christlieb N.,
Aquilina S.E., Rozanski T., Cordoni C.
<Mon. Not. R. Astron. Soc. 546, stag170 (2026)>
=2026MNRAS.546g0170L 2026MNRAS.546g0170L (SIMBAD/NED BibCode)
ADC_Keywords: Milky Way ; Stars, population II ; Abundances ; Optical
Keywords: stars: abundances - stars: Population II - Galaxy: abundances
Abstract:
We present a detailed chemical analysis study of 16 candidate
metal-poor stars, previously identified with 2dF+AAOmega, using
X-Shooter spectra and the Korg 1D LTE spectral synthesis code. We
generally confirm the earlier metallicity estimates and reveal six EMP
([Fe/H]←3) stars in the current sample. Two of these stars,
including the most metal-poor at [Fe/H]=-3.89±0.07, are
kinematically associated with the GSE accretion event, increasing the
number of known GSE stars with [Fe/H]←3.5 to eight. From the
X-Shooter spectra we determine abundances for 16 elements, with the
element-to-iron abundance ratios generally consistent with
high-resolution studies of Galactic halo stars. Within the sample, we
identify three peculiar stars: the first is a GSE nitrogen enhanced
metal poor (NEMP; [N/Fe]=1.60±0.10 and [C/Fe]=0.23±0.08)
star with unusually high Na ([Na/Fe]=2.26±0.07) and Li
(A(Li)3DNLTE=1.90±0.08) abundances, but lacking enhancements in
[Al/Fe] or [Mg/Fe]. The second is a halo r-II star significantly
enhanced in Sr ([Sr/Ba]=0.39±0.08), suggesting mixture of r-process
and s-process enrichment, uncommon for r-II stars. Whilst the third is
a halo star very depleted in N ([N/Fe]←1.13), with low C
([C/Fe]=-0.33±0.08) and otherwise 'normal' [X/Fe] abundances,
suggesting enrichment with Type II supernova that proceeds enrichment
from massive AGB stars. This study reveals the substantial degree of
chemical diversity in the stellar populations which assembled the
early Milky Way.
Description:
We have all tables presented in the manuscript, alongside additional
supplementary datasets for our 16 metal-poor stars studied in this
work. These include observing details for the program stars, chemical
abundances for the sample, and fitting windows used in the 1D LTE
spectral synthesis fitting code Korg.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 188 16 Program stars and observational parameters
table2.dat 103 16 Observing details
table3.dat 67 17 Median abundance errors
table4.dat 172 16 Stellar parameters
table5.dat 143 253 Chemical abundances
table6.dat 127 15 [C/N] abundances
table7.dat 97 16 [alpha/Fe] abundances
table8.dat 140 16 [Sr/Ba] and [Ba/H] abundances
tables1.dat 32 34 Windows used for abundance determination
tables2.dat 42 24 Na windows used for each star
tables3.dat 73 48 CaII NLTE corrections and continuum offsets
tables4.dat 22 16 Evolutionary corrections for CH
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See also:
I/355 : Gaia DR3 Part 1. Main source (Gaia Collaboration, 2022)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 17 A17 --- StarId Star source identifier
19- 37 I19 --- GaiaDR3 Gaia DR3 source identifier
39- 57 F19.15 deg RAdeg Right ascension (J2016)
59- 77 F19.15 deg DEdeg Declination (J2016)
79- 98 F20.16 deg GLON Galactic longitude
100-118 F19.15 deg GLAT Galactic latitude
120-138 F19.16 mas plx Parallax
140-150 F11.9 mas e_plx Parallax error
152-160 F9.6 mag Gmag Gaia DR3 G apparent magnitude
162-179 F18.16 mag E(B-V)corr Reddening correction (1)
181-188 A8 --- Orbit Orbit classification (1) (2)
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Note (1): Taken from Lowe et al. (2025PASA...42...40L 2025PASA...42...40L).
Note (2): There are three kinematic groups as follows:
pro_disk = Prograde Disk
halo = Halo
gse = Gaia-Sausage Enceladus
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 17 A17 --- StarId Star source identifier
19 I1 --- Nobs Number of exposures taken
21- 24 I4 s ExpTime Exposure length
26- 43 F18.14 --- snrUVB Signal-to-noise in UVB (1)
45- 62 F18.14 --- snrVIS Signal-to-noise in VIS (1)
64- 84 F21.16 km/s RVavg Average heliocentric radial velocity (2)
86-103 F18.16 km/s e_RVavg Heliocentric radial velocity error
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Note (1): Extracted from the ESO Science Program reduction files.
Note (2): Averages of radial velocities measured from both the UVB
(H-Delta, H-Gamma and H-Beta) and the VIS (H-Alpha and
the CaII triplet).
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 5 A5 --- El Element identifier
7- 25 F19.17 [-] e[X/Fe]Teff ? Median error of [X/Fe] when perturbing
Teff by +100K
27- 46 F20.18 [-] e[X/Fe]logg ? Median error of [X/Fe] when perturbing
logg by +0.3dex
48- 67 F20.18 [-] e[X/Fe]vmic ? Median error of [X/Fe] when perturbing
vmic by +0.3km/s
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 17 A17 --- StarId Star source identifier
19- 35 F17.12 K Teff Effective temperature (1)
37- 55 F19.15 K e_Teff Uncertainty in teff (1)
57- 74 F18.16 [cm/s2] logg Surface gravity (1)
76- 93 F18.16 [cm/s2] e_logg Uncertainty in logg (1)
95-113 F19.16 [-] [Fe/H] Metallicity [Fe/H]
115-132 F18.16 [-] e_[Fe/H] Uncertainty in [Fe/H]
134-151 F18.16 km/s vmic Microturbulence velocity (2)
153-172 F20.18 km/s e_vmic Microturbulence velocity error
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Note (1): Taken from Lowe et al. (2025PASA...42...40L 2025PASA...42...40L).
Note (2): Calculated using equation 4 from Buder et al. (2025PASA...42...51B 2025PASA...42...51B).
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Byte-by-byte Description of file: table5.dat
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Bytes Format Units Label Explanations
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1- 17 A17 --- StarId Star source identifier
19- 23 A5 --- El Element identifier
25 A1 --- Det [Y/N] Detection of element (1)
27- 45 F19.16 [-] [X/Fe] ? Abundance [X/Fe] (2)
47- 64 F18.16 [-] e_[X/Fe] ? Uncertainty in [X/Fe] (2)
66- 84 F19.16 [-] [X/Fe]ul ? Upperlimit in [X/Fe] (3)
86-104 F19.16 [-] [X/H] ? Abundance [X/H] (2)
106-123 F18.16 [-] e_[X/H] ? Uncertainty in [X/H] (2)
125-143 F19.16 [-] [X/H]ul ? Upperlimit in [X/H] (3)
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Note (1): 'Y' if detection, otherwise 'N'.
Note (2): Only applicable if detection is 'Y', otherwise NaN.
Note (3): Only applicable if detection is 'N', otherwise NaN.
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Byte-by-byte Description of file: table6.dat
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Bytes Format Units Label Explanations
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1- 17 A17 --- StarId Star source identifier (1)
19 A1 --- Det [Y/N] Detection of element (2)
21- 39 F19.16 [-] [N/Fe] ? [N/Fe] abundance (3)
41- 58 F18.16 [-] e_[N/Fe] ? Uncertainty in [N/Fe] (3)
60- 64 F5.2 [-] [N/Fe]ul ? Upperlimit in [N/Fe] (4)
66- 85 F20.17 [-] [C/N] ? [C/N] abundance (3)
87-105 F19.17 [-] e_[C/N] ? Uncertainty in [C/N] (3)
107-127 F21.18 [-] [C/N]ll ? Lowerlimit in [C/N] (4)
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Note (1): Stars with upperlimits in both [N/Fe] and [C/Fe] are excluded.
Note (2): 'Y' if detection, otherwise 'N'.
Note (3): Only applicable if detection is 'Y', otherwise NaN.
Note (4): Only applicable if detection is 'N', otherwise NaN.
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Byte-by-byte Description of file: table7.dat
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Bytes Format Units Label Explanations
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1- 17 A17 --- StarId Star source identifier
19- 37 F19.16 [-] [Fe/H] Metallicity [Fe/H]
39- 56 F18.16 [-] e_[Fe/H] Uncertainty in [Fe/H]
58- 76 F19.17 [-] [alpha/Fe] Abundance [alpha/Fe] (1)
78- 97 F20.18 [-] e_[alpha/Fe] Uncertainty in [Alpha/Fe]
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Note (1): Weighted mean between Mg, Si, Ca and Ti.
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Byte-by-byte Description of file: table8.dat
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Bytes Format Units Label Explanations
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1- 17 A17 --- StarId Star source identifier
19 A1 --- Det [Y/N] Detection of element (1)
21- 39 F19.16 [-] [Ba/H] ? Abundance [Ba/H] (2)
41- 58 F18.16 [-] e_[Ba/H] ? Uncertainty in [Ba/H] (2)
60- 78 F19.16 [-] [Ba/H]ul ? Upperlimit in [Ba/H] (3)
79- 98 F20.17 [-] [Sr/Ba] ? Abundance [Sr/Ba] (2)
100-118 F19.17 [-] e_[Sr/Ba] ? Uncertainty in [Sr/Ba] (2)
120-140 F21.18 [-] [Sr/Ba]ll ? Lowerlimit in [Sr/Ba] (3)
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Note (1): 'Y' if detection, otherwise 'N'.
Note (2): Only applicable if detection is 'Y', otherwise NaN.
Note (3): Only applicable if detection is 'N', otherwise NaN.
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Byte-by-byte Description of file: tables1.dat
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Bytes Format Units Label Explanations
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1- 5 A5 --- El Element identifier
7- 14 F8.3 0.1nm Line Rest wavelength of line (1)
16- 23 F8.3 0.1nm Wavemin Minimum wavelength for fitting window
25- 32 F8.3 0.1nm Wavemax Maximum wavelength for fitting window
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Note (1): Taken from VALD.
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Byte-by-byte Description of file: tables2.dat
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Bytes Format Units Label Explanations
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1- 17 A17 --- StarId Star source identifier (1)
19- 26 F8.3 0.1nm Line Rest wavelength of line (2)
28- 35 F8.3 0.1nm Wavemin Minimum wavelength for fitting window
37- 42 F6.1 0.1nm Wavemax Maximum wavelength for fitting window
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Note (1): Stars with interstellar Na contamination in both Na D-lines are
excluded.
Note (2): Taken from VALD.
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Byte-by-byte Description of file: tables3.dat
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Bytes Format Units Label Explanations
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1- 17 A17 --- StarId Star source identifier
19- 26 F8.3 0.1nm Line Rest wavelength of line
28- 33 F6.3 --- cntmOffset Continuum offset for synthetic spectra
35- 53 F19.16 [-] NLTEcorr NLTE correction for CaII (1)
55- 73 F19.16 [-] [Ca/Fe] NLTE-corrected [Ca/Fe] abundance
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Note (1): NLTE corrections taken from Osorio et al. (2022ApJ...928..173O 2022ApJ...928..173O), then
interpolated using a piecewise linear interpolator.
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Byte-by-byte Description of file: tables4.dat
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Bytes Format Units Label Explanations
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1- 17 A17 --- StarId Star source identifier
19- 22 F4.2 [-] [C/Fe]corr Evolutionary Correction (1)
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Note (1): Corrections were calculated using the vplacco web interface
(https://vplacco.pythonanywhere.com/). This uses grids from
Placco et al. (2014ApJ...797...21P 2014ApJ...797...21P).
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Acknowledgements:
Benjamin Lowe, ben.lowe(at)anu.edu.au
(End) Benjamin D. C. Lowe [ANU], Patricia Vannier [CDS] 02-Feb-2026