J/A+A/707/A280 Member stars abund. of MgAl burning chain in M54 (Alvarez+, 2026)
MgAl burning chain in M 54:
The globular cluster-like properties of a nuclear star cluster.
Alvarez Garay D.A., Mucciarelli A., Ventura P., Bellazzini M., Covella S.
<Astron. Astrophys. 707, A280 (2026)>
=2026A&A...707A.280A 2026A&A...707A.280A (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, globular ; Abundances ; Spectroscopy ; Optical ;
Radial velocities ; Effective temperatures ; Velocity dispersion
Keywords: stars: abundances - stars: general - stars: low-mass
Abstract:
In this study, we present the chemical abundances of Fe, Mg, Al, Si,
and K for a sample of 233 likely member stars of M 54. All the stars
were observed with the FLAMES high-resolution multi-object
spectrograph mounted at the VLT. Our analysis confirmed the presence
of a large metallicity range in M 54, with the majority of the stars
having -1.8<[Fe/H]←1.0 dex and few stars with [Fe/H]>-1.0dex. The
mean value of the total sample is [Fe/H]=-1.40 (sigma=0.22dex). A MCMC
analysis revealed that the observed spread in [Fe/H] is compatible
with a non-null intrinsic iron dispersion. We also found that the
metallicity distribution function and the broadening of the red giant
branch of M 54 are not compatible with a single age, but instead they
suggest a wide age range from about 13 Gyr to about 1-2Gyr or a
smaller age range if a significant He enhancement (Y=0.35/0.40) is
present in the most metal-rich stars. We identified among the stars in
M 54 the entire pattern of anticorrelations linked to the MgAl burning
cycle. In particular, the metal-rich component displays a higher level
of H-burning with the presence of more extended anticorrelations than
the metal-poor component. No Mg-poor ([Mg/Fe]<0.0dex) stars are
identified in M 54. The evidence collected so far cannot be explained
neither with a GC-like scenario nor with a galactic chemical
evolution. The chemical properties of M 54 can be explained within a
scenario where this system formed through the merging of two globular
clusters, the metal-poor one with standard characteristics and the
more metal-rich one with more pronounced chemical anomalies, a
possibly younger than the first one. M 54 is confirmed as a key
stellar system for explaining the chemical evolution of a nuclear star
cluster.
Description:
The table2.dat the star name, the Gaia G magnitude, the radial
velocity and its uncertainty, the surface temperature, the logg, the
microturbulent velocity, the abundance of Fe and its uncertainty, the
abundance of Mg and its uncertainty, the abundance of Al and its
uncertainty, the abundance of Si and its uncertainty, and the
abundance of K and its uncertainty. 99.99 stands for no measured
abundance.
Objects:
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RA (2000) DE Designation(s)
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18 55 03.33 -30 28 47.4 M 54 = C 1851-305
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 125 233 Stellar parameters and chemical abundances of
likely member stars of M 54 observed with FLAMES
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See also:
I/355 : Gaia DR3 Part 1. Main source (Gaia Collaboration, 2022)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 11 A11 --- ID Star name identifier number, M54_NNNNNNN (ID)
13- 31 I19 --- GaiaDR3 Gaia DR3 star name (ID_Gaia)
33- 39 F7.4 mag Gmag Gaia DR3 G magnitude (G0)
41- 46 F6.2 km/s RV Radial velocity (RV)
48- 51 F4.2 km/s e_RV Error in radial velocity (eRV)
53- 56 I4 K Teff Surface temperature (Teff)
58- 61 F4.2 [cm/s2] logg Logarithm of star gravity (logg)
63- 66 F4.2 km/s Vt Microturbolent velocity (v_t)
68- 72 F5.2 [Sun] [Fe/H] Abundance relative to the Sun for FeI
([Fe/H])
74- 77 F4.2 [Sun] e_[Fe/H] Uncertainty on the abundance for FeI
(e[Fe/H])
79- 83 F5.2 [Sun] [Mg/Fe] ?=99.99 Abundance relative to the Sun for
MgI ([Mg/Fe])
85- 89 F5.2 [Sun] e_[Mg/Fe] ?=99.99 Uncertainty on the abundance for MgI
(e[Mg/Fe])
91- 95 F5.2 [Sun] [Al/Fe] ?=99.99 Abundance relative to the Sun for
AlI ([Al/Fe])
97-101 F5.2 [Sun] e_[Al/Fe] ?=99.99 Uncertainty on the abundance for AlI
(e[Al/Fe])
103-107 F5.2 [Sun] [Si/Fe] ?=99.99 Abundance relative to the Sun for
SiI ([Si/Fe])
109-113 F5.2 [Sun] e_[Si/Fe] ?=99.99 Uncertainty on the abundance for SiI
(e[Si/Fe])
115-119 F5.2 [Sun] [K/Fe] ?=99.99 Abundance relative to the Sun for KI
([K/Fe])
121-125 F5.2 [Sun] e_[K/Fe] ?=99.99 Uncertainty on the abundance for KI
(e[K/Fe])
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Acknowledgements:
Deimer Antonio Alvarez Garay, deimer.alvarez(at)inaf.it
(End) Luc Trabelsi [CDS] 29-Jan-2026