J/MNRAS/537/1984 CEMP prediction abundances (Ardern-Arentsen+, 2025)
Predicting metallicities and carbon abundances from Gaia XP spectra for
(carbon-enhanced) metal-poor stars.
Ardern-Arentsen A., Kane S.G., Belokurov V., Matsuno T., Montelius M.,
Monty S., Sanders J.L.
<Mon. Not. R. Astron. Soc. 537, 1984-2002 (2025)>
=2025MNRAS.537.1984A 2025MNRAS.537.1984A (SIMBAD/NED BibCode)
ADC_Keywords: Stars, carbon ; Abundances ; Optical
Keywords: methods: data analysis - stars: abundances -
stars: chemically peculiar - stars: Population II - Galaxy: halo
Abstract:
Carbon-rich (C-rich) stars can be found at all metallicities and
evolutionary stages. They are often the result of mass-transfer from a
companion, but some of the most metal-poor C-rich objects are likely
carrying the imprint of the metal-free First Stars from birth. In this
work, we employ a neural network to predict metallicities and carbon
abundances for over 10 million stars with Gaia low-resolution XP
spectra, down to [Fe/H]=-3.0 and up to [C/Fe]≃+2. We identify
∼2000 high-confidence bright (G<16) carbon-enhanced metal-poor (CEMP)
stars with [Fe/H]←2.0 and [C/Fe]>+0.7. The majority of our C-rich
candidates have [Fe/H]>-2.0 and are expected to be binary
mass-transfer products, supported by high barium abundances in GALAH
and/or their Gaia RUWE and radial velocity variations. We confirm
previous findings of an increase in C-rich stars with decreasing
metallicity, adopting a definition of 3σ outliers from the
[C/Fe] distribution, although our frequency appears to flatten for
-3.0<[Fe/H]←2.0 at a level of 6-7%. We also find that the fraction of
C-rich stars is low among globular cluster stars (connected to their
lower binary fraction), and that it decreases for field stars more
tightly bound to the Milky Way. We interpret these last results as
evidence that disrupted globular clusters contribute more in the inner
Galaxy, supporting previous work. Homogeneous samples like these are
key to understanding the full population properties of C-rich stars,
and this is just the beginning.
Description:
To predict Teff, logg and [M/H] from the XP spectra of Gaia stars,
Andrae et al. (2023ApJS..267....8A 2023ApJS..267....8A, hereafter A23) used the XGBoost
algorithm trained on APOGEE data. They augmented it with the Li et al.
(2022ApJ...931..147L 2022ApJ...931..147L, Cat. J/ApJ/931/147) sample of VMP stars to improve
the predictions at low-metallicity, and they show that their
metallicity predictions work well down to [M/H] ∼ -3.0. This work does
not take into account carbon as a variable, which has many molecular
features across the XP wavelength range, so for CEMP stars their [M/H]
does not correspond tightly to [Fe/H].
To identify CEMP stars among the many Gaia DR3 stars with XP
spectra, Lucey et al. (2023MNRAS.523.4049L 2023MNRAS.523.4049L, Cat. J/MNRAS/523/4049,
hereafter L23) applied the XGBoost algorithm to all XP spectra for
stars with 0.8<(BP-RP)<2.75 and MG<7 - ∼ 183 million in total. Bluer
stars are likely too hot to produce good estimates for whether a star
is carbon-rich or not, because the molecular features become too weak,
and redder and fainter absolute magnitude stars are lacking from their
training sample. For each star, their XGBoost setup predicts the
probability Pc that a star is carbon-enhanced, according to the
typical [C/Fe]>0.7 definition. We will refer to these as C-rich
candidates. The reference sample that L23 used to train and test their
method comes from the low-resolution part of the Sloan Digital Sky
Survey (SDSS, York et al. 2000AJ....120.1579Y 2000AJ....120.1579Y), specifically the
low-resolution optical side (mostly the Sloan Extension for Galactic
Understanding and Exploration (SEGUE) project).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
ref.dat 463 2807 Reference sample
l23.dat 431 58871 Lucey et al. (2023MNRAS.523.4049L 2023MNRAS.523.4049L,
Cat. J/MNRAS/523/4049) sample predictions
a23.dat 510 10483688 XP vetted giants sample from Andrae et al.
(2023ApJS..267....8A 2023ApJS..267....8A)
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See also:
I/355 : Gaia DR3 Part 1. Main source (Gaia Collaboration, 2022)
J/ApJ/931/147 : Very metal-poor stars with LAMOST + Subaru. II. (Li+, 2022)
J/MNRAS/523/4049 : CEMP in Gaia DR3 (Lucey+, 2023)
Byte-by-byte Description of file: ref.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 19 I19 --- GaiaDR3 Gaia DR3 source_id (source_id)
21- 40 F20.16 deg RAdeg Gaia DR3 right ascension (ICRS)
at Ep=2016.0 (ra)
42- 61 F20.16 deg DEdeg Gaia DR3 declination (ICRS)
at Ep=2016.0 (dec)
63- 72 F10.7 mag Gmag Gaia DR3 G magnitude (photgmean_mag)
74- 97 F24.20 mas plx ? Gaia DR3 parallax (parallax)
99-111 F13.10 mas e_plx ? Gaia DR3 parallax_error (parallax_error)
113-119 E7.2 --- pvar Probability star is photometric variable
(pvar)
121-132 F12.10 --- E(B-V) SFD E(B-V) (ebv)
134-154 F21.18 mag (BP-RP)0 Extinction-corrected BP-RP (BPRP_0)
156-173 F18.15 mag Gmag0 Extinction-corrected G (G_0)
175-182 F8.3 K Teff-spec Spectroscopic effective temperature
(teff_spec)
184-189 F6.3 --- [Fe/H]-spec Spectroscopic [Fe/H] (feh_spec)
191-196 F6.3 --- [C/Fe]-spec Spectroscopic [C/Fe] (cfe_spec)
198-202 F5.3 [cm/s2] logg-spec Spectroscopic surface gravity (logg_spec)
204-221 F18.13 K Teff Predicted effective temperature (teff)
223-241 F19.16 --- [Fe/H] Predicted [Fe/H] (feh)
243-261 F19.16 --- [C/Fe] Predicted [C/Fe] (cfe)
263-280 F18.16 [cm/2] logg Predicted surface gravity (logg)
282-300 F19.15 K e_Teff Predicted teff error (err_teff)
302-319 F18.16 --- e_[Fe/H] Predicted [Fe/H] error (err_feh)
321-338 F18.16 --- e_[C/Fe] Predicted [C/Fe] error (err_cfe)
340-357 F18.16 [cm/2] e_logg Predicted logg error (err_logg)
359-376 F18.14 K s_Teff Standard deviation of teff predictions
(std_teff)
378-395 F18.16 --- s_[Fe/H] Standard deviation of [Fe/H] predictions
(std_feh)
397-414 F18.16 --- s_[C/Fe] Standard deviation of [C/Fe] predictions
(std_cfe)
416-433 F18.16 [cm/2] s_logg Standard deviation of logg predictions
(std_logg)
435-459 A25 --- Cat Reference for spectroscopic values
(cat) (1)
461-463 F3.1 --- train [0/1] Equal to 1 if used in training and
0 if used for testing (train)
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Note (1): References as follows:
Li et al. (2022) = 2022ApJ...931..147L 2022ApJ...931..147L, Cat. J/ApJ/931/147
Yoon et al. (2016) = 2016ApJ...833...20Y 2016ApJ...833...20Y, Cat. J/ApJ/833/20
this work (L23 LAMOST) = this work, Lucey et al. (2023MNRAS.523.4049L 2023MNRAS.523.4049L,
Cat. J/MNRAS/523/4049) and LAMOST stars
this work (normal LAMOST) = this work, "normal" LAMOST stars
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Byte-by-byte Description of file: l23.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 19 I19 --- GaiaDR3 Gaia DR3 source_id (source_id)
21- 40 F20.16 deg RAdeg Gaia DR3 right ascension (ICRS)
at Ep=2016.0 (ra)
42- 62 E21.15 deg DEdeg Gaia DR3 declination (ICRS)
at Ep=2016.0 (dec)
64- 73 F10.7 mag Gmag Gaia DR3 G magnitude (photgmean_mag)
75- 98 E24.17 mas plx Gaia DR3 parallax (parallax)
100-111 F12.10 mas e_plx Gaia DR3 parallax error (parallax_error)
113-119 E7.2 --- pvar ? Probability star is photometric variable (
pvar)
121-133 F13.10 --- E(B-V) SFD E(B-V) (ebv)
135-158 E24.17 mag (BP-RP)0 ?=- Extinction-corrected BP-RP (BPRP_0)
160-183 E24.17 mag Gmag0 ?=- Extinction-corrected G (G_0)
185-202 F18.13 K Teff Predicted effective temperature (teff)
204-223 F20.16 --- [Fe/H] Predicted [Fe/H] (feh)
225-247 E23.16 --- [C/Fe] Predicted [C/Fe] (cfe)
249-271 E23.16 [cm/s2] logg Predicted surface gravity (logg)
273-292 F20.15 K e_Teff Predicted teff error (err_teff)
294-312 F19.16 --- e_[Fe/H] Predicted [Fe/H] error (err_feh)
314-332 F19.16 --- e_[C/Fe] Predicted [C/Fe error (err_cfe)
334-351 F18.16 [cm/s2] e_logg Predicted logg error (err_logg)
353-372 F20.15 K s_Teff Standard deviation of teff predictions
(std_teff)
374-392 F19.16 --- s_[Fe/H] Standard deviation of [Fe/H] predictions
(std_feh)
394-412 F19.16 --- s_[C/Fe] Standard deviation of [C/Fe] predictions
(std_cfe)
414-431 F18.16 [cm/s2] s_logg Standard deviation of logg predictions
(std_logg)
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Byte-by-byte Description of file: a23.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 19 I19 --- GaiaDR3 Gaia DR3 source_id (source_id)
21- 40 F20.16 deg RAdeg Gaia DR3 right ascension (ICRS)
at Ep=2016.0 (ra)
42- 64 E23.15 deg DEdeg Gaia DR3 declination (ICRS)
at Ep=2016.0 (dec)
66- 75 F10.7 mag Gmag Gaia DR3 G magnitude (photgmean_mag)
77- 95 F19.16 mas plx Gaia DR3 parallax (parallax)
97-108 F12.10 mas e_plx Gaia DR3 parallax_error (parallax_error)
110-117 E8.3 --- pvar ? Probability star is photometric variable
(pvar)
119-128 F10.6 --- E(B-V) SFD E(B-V) (ebv)
130-153 E24.17 mag (BP-RP)0 ?=- Extinction-corrected BP-RP (BPRP_0)
155-178 E24.17 mag Gmag0 ?=- Extinction-corrected G (G_0)
180-200 F21.15 K Teff Predicted effective temperature (teff)
202-224 E23.16 --- [Fe/H] Predicted [Fe/H] (feh)
226-248 E23.16 --- [C/Fe] Predicted [C/Fe] (cfe)
250-269 F20.16 [cm/s2] logg Predicted surface gravity (logg)
271-290 F20.15 K e_Teff Predicted teff error (err_teff)
292-310 F19.16 --- e_[Fe/H] Predicted [Fe/H] error (err_feh)
312-329 F18.16 --- e_[C/Fe] Predicted [C/Fe error (err_cfe)
331-349 F19.16 [cm/s2] e_logg Predicted logg error (err_logg)
351-371 E21.15 K s_Teff Standard deviation of teff predictions
(std_teff)
373-393 E21.16 --- s_[Fe/H] Standard deviation of [Fe/H] predictions
(std_feh)
395-415 E21.16 --- s_[C/Fe] Standard deviation of [C/Fe] predictions
(std_cfe)
417-438 E22.16 [cm/s2] s_logg Standard deviation of logg predictions
(std_logg)
440-460 F21.19 --- Ccor ? Evolutionary carbon correction (Ccor)
462-484 F23.15 km2/s2 Energy Orbital energy (energy)
486-510 F25.18 km.kpc/s Lz Angular momentum (Lz)
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Acknowledgements:
Anke Ardern-Arentsen, anke.arentsen(at)ast.cam.ac.uk
(End) Patricia Vannier [CDS] 19-Jan-2025