  In this study, we report the results of Fe, Mg, Al, and Si abundances
analysis for a sample of 439 stars in Omega Centauri, using high-resolution
spectra obtained with the VLT/FLAMES multi-object spectrograph. Our analysis
reveals the presence of four distinct Fe populations, with the main peak
occurring at low metallicity, consistent with previous literature findings. We
observe a discrete and pronounced Mg-Al anti-correlation, which exhibits
variations in shape and extension as a function of metallicity. Specifically,
this anti-correlation is present in stars with metallicities lower than
approximately -1.3 dex, while it becomes less evident or absent for higher
[Fe/H] values. Additionally, we detect (anti-) correlations between Mg and Si,
and between Al and Si, whose extensions also vary with metallicity, similar to
the Mg-Al anti-correlation. These results suggest that the MgAl cycle plays a
crucial role in the formation of multiple populations in Omega Centauri, with
the presence of all (anti-) correlations at metallicities lower than -1.3 dex
providing evidence for the burning of Mg at very high temperatures (> 10^8 K),
at least in the metal-poor regime. Furthermore, we observe a clear trend of
stars with [Al/Fe] > +0.5 dex as a function of metallicity, confirming for the
first time the existence of the two channels of Al production and destruction.
This evidence can help to provide further constraints on the potential nature
of the polluters responsible for the observed chemical anomalies in this
stellar system. Finally, we find that the two most metal-poor populations
identified in our sample are compatible with null or very small metallicity
dispersion and we discuss how this result fit into a scenario where Omega
Centauri is the remnant of a disrupted nucleated dwarf galaxy.
