J/A+A/712/A219 Iron Spread in globular clusters (Schiappacasse-Ulloa+, 2026)
Intrinsic iron abundance spreads in globular clusters.
Schiappacasse-Ulloa J., Lucatello S., Magrini L., Bragaglia A., Carretta E.
<Astron. Astrophys. 712, A219 (2026)>
=2026A&A...712A.219S 2026A&A...712A.219S (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, globular ; Stars, population II ; Spectroscopy ;
Abundances, [Fe/H]
Keywords: stars: Population II - stars: abundances -
globular clusters: general - globular clusters: individual: NGC3201 -
globular clusters: individual: NGC5634 -
globular clusters: individual: NGC1851
Abstract:
Globular clusters host multiple stellar populations, likely composed
of a subset of first-generation stars that enriched the intracluster
medium and gave rise to second-generation (SG) stars, each
characterised by distinctive chemical patterns. These patterns
typically include enhancements in elements such as N, Na, and Al,
coupled with depletions in C, O, and Mg in SG stars.
Traditionally, heavier elements such as those in the iron peak were
considered unaffected in most clusters. However, recent studies have
reported significant internal spreads in these elements, suggesting a
more complex picture of chemical enrichment within globular clusters.
This study seeks to derive precise and homogeneous differential iron
abundances in a large sample of globular clusters. By doing so, our
aim is to investigate the presence of intrinsic iron spreads within
them and to assess the existence of differences in Fe between their
stellar populations.
We used the Python-based tool Q2 to determine both differential
stellar parameters and iron abundances for 92 sibling stars -- defined
by the similarities in their stellar parameters -- across 13 Galactic
globular clusters. This differential approach reduces the influence of
non-local thermodynamic equilibrium effects, and minimises
observational errors, and systematic biases linked to stellar
parameters. We performed Monte Carlo simulations to evaluate the
statistical significance of the measured spreads.
Most of the globular clusters in our sample do not show evidence of
statistically significant iron spreads. Only a few exceptions emerge,
namely NGC1851, NGC3201, and NGC5634, which display a highly
significant iron spread. In particular, NGC3201 shows a particularly
pronounced spread in its first-generation population, reflecting a
potential inhomogeneous iron abundance in its pristine material.
Finally, through statistical tests, we conclude that our data do not
support the presence of a widespread iron variation in globular
clusters.
Description:
Description of the 92 stars belonging to the 13 Galactic globular
clusters analysis in the present study. The table contains information
about the stellar parameters (Teff, logg, [Fe/H], and
microturbulence), as well as, the differential iron abundance derived
to study the potential internal iron spreads.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 111 92 Position, stellar parameter, and differential
iron abundance in 13 globular clusters
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Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 7 A7 --- Cluster Globular cluster name
9- 17 A9 --- ID Identification name of the star
19- 30 F12.8 deg RAdeg Right Ascension (J2000)
32- 43 F12.8 deg DEdeg Declination (J2000)
45- 48 I4 K Teff Effective temperature
50- 51 I2 K e_Teff Effective temperature error
59- 62 F4.2 [cm/s2] logg Surface gravity
64- 67 F4.2 [cm/s2] e_logg Surface gravity error
73- 77 A5 --- [Fe/H] Metallicity (dex)
79- 82 F4.2 --- e_[Fe/H] Metallicity error (dex)
87- 90 F4.2 km/s vt microturbulent velocity
92- 95 F4.2 km/s e_vt microturbulent velocity error
99-104 F6.3 --- DeltaFe Differential Fe abundance (dex)
108-111 F4.2 --- e_DeltaFe Differential Fe abundance error (dex)
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Acknowledgements:
Jose Schiappacasse-Ulloa, jose.schiappacasse(at)inaf.it
License: CC-BY-4.0
(End) J. Schiappacasse-Ulloa [INAF-OAA, Italy], P. Vannier [CDS] 16-Jul-2026