J/A+A/705/A31 Eu abundance in the Small Magellanic Cloud (Anoardo+, 2026)
The chemical DNA of the Magellanic Clouds.
IV. Unveiling extreme element production: The Eu abundance in the
Small Magellanic Cloud.
Anoardo S., Mucciarelli A., Palla M., Santarelli L., Lardo C., Romano D.
<Astron. Astrophys. 705, A31 (2026)>
=2026A&A...705A..31A 2026A&A...705A..31A (SIMBAD/NED BibCode)
ADC_Keywords: Magellanic Clouds ; Stars, giant ; Abundances ; Spectroscopy ;
Optical
Keywords: galaxies: abundances - Local Group - Magellanic Clouds
Abstract:
In this study we investigate the chemical enrichment of the rapid
neutron-capture process in the Small Magellanic Cloud (SMC). We
measure [Eu/Fe] abundance ratios in 209 giant stars that are confirmed
members of the SMC, providing the first extensive dataset of Eu
abundances in this galaxy across its full metallicity range, spanning
more than 1.5dex. We compare Eu abundances with those of Mg and Ba to
evaluate the efficiency of the r-process relative to alpha-capture and
s-process nucleosynthesis. The SMC shows enhanced [Eu/Fe] values at
all metallicities (comparable with the values measured in the Milky
Way), with a clear decline as [Fe/H] increases (from ~-1.75dex to
~-0.5dex), consistent with the onset of Type Ia supernovae. In
contrast, [Eu/Mg] is enhanced by about +0.5dex at all [Fe/H],
significantly above the values observed in Milky Way stars, where
[Eu/Mg] remains close to solar, reflecting comparable production of
r-process and alpha-capture elements. Moreover, [Ba/Eu] increases with
metallicity, beginning at [Fe/H]~=-1.5dex, namely at a lower
metallicity with respect to the Milky Way, where [Ba/Eu] starts to
increase around [Fe/H]~=-1dex. Our findings suggest the SMC has a
higher production of Eu (with respect to the alpha-elements) than the
Milky Way but in line with what observed in other dwarf systems within
the Local Group. We confirm that galaxies with star formation
efficiencies lower than the Milky Way have high [Eu/alpha], probably
indicating a stronger efficiency of the delayed sources of r-process
at low metallicities.
Description:
Table 1 includes identification, coordinates and G magnitudes from the
Gaia Data Release 3, heliocentric radial velocity and its uncertainty,
the name of the star as used in Paper I, the field and the possibility
(flagged with *) that the target star is part of a binary system. We
refer to Mucciarelli et al. (2023A&A...671A.124M 2023A&A...671A.124M, Cat. J/A+A/671/A124)
as Paper I.
Table 2 includes identification from Gaia Data Release 3, the
atmospheric parameters and the chemical abundance ratios.
Uncertainties in [Eu/Fe] equal to 9.99 indicate that the given
abundance ratio is an upper limit.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 92 209 Main information of the observed targets
table2.dat 67 209 Stellar parameters and chemical abundances of
the observed targets
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See also:
I/355 : Gaia DR3 Part 1. Main source (Gaia Collaboration, 2022)
J/A+A/671/A124 : 206 SMC red giants chemical composition (Mucciarelli+, 2023)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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2- 20 I19 --- GaiaDR3 Gaia DR3 identification number
22- 31 F10.7 deg RAdeg Right ascension (ICRS at Ep=2016.0)
33- 43 F11.7 deg DEdeg Declination (ICRS at Ep=2016.0)
45- 51 F7.4 --- Gmag G magnitude (Gaia DR3)
53- 58 F6.2 km/s RV Heliocentric radial velocity
61- 64 F4.2 km/s e_RV Uncertainty on radial velocity
69- 82 A14 --- IDPapI Star name as in Paper I (FLD-NNN_NNNNNN),
[MMB2023] FLD-NNN NNNNNN in Simbad
84- 90 A7 --- Field Target field of the star (FLD-NNN)
92 A1 --- Binary [*] Possibility that the star is a binary (*)
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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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2- 20 I19 --- GaiaDR3 Gaia DR3 identification number
22- 25 I4 K Teff Effective temperature
27- 30 F4.2 [cm/s2] logg Surface gravity
32- 34 F3.1 km/s vt Microturbulent velocity
36- 40 F5.2 --- [Fe/H] Abundance relative to the Sun for FeI
42- 45 F4.2 --- e_[Fe/H] Uncertainty on the abundance for FeI
47 A1 --- l_[Eu/Fe] Limit flag on [Eu/Fe]
48- 51 F4.2 --- [Eu/Fe] Abundance relative to the Sun for EuII
53- 56 F4.2 --- e_[Eu/Fe] ?=9.99 Uncertainty on the abundance
for EuII (1)
58- 62 F5.2 --- [Ba/Fe] Abundance relative to the Sun for BaII
64- 67 F4.2 --- e_[Ba/Fe] Uncertainty on the abundance for BaII
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Note (1): If e_[Eu/Fe]=9.99, then the corresponding [Eu/Fe] ratio is an upper
limit.
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Acknowledgements:
Samuele Anoardo, samuele.anoardo(at)studio.unibo.it
(End) Patricia Vannier [CDS] 13-Nov-2025