Low- to intermediate-mass stars ascend the Asymptotic Giant Branch (AGB) at the end of their stellar evolution. These stars are critical sites for heavy-element nucleosynthesis and dust production, contribute to galaxy luminosities at IR wavelengths, and ultimately evolve into planetary nebulae. AGB evolution is driven by intense stellar mass loss — a process that dictates the star's final fate and also dominates the chemical enrichment of the interstellar medium. OH/IR stars represent a heavily dust-obscured, IR-bright phase of oxygen-rich stars in the late AGB, having high mass-loss rates. In this talk, I will present multi-wavelength observations, led by spatially-resolved ALMA CO spectral line data, paired with SEDs and photometry, for a sample of 77 equidistant OH/IR stars in the inner Galactic bulge. These data allow us to trace the transformations occurring in the mass-loss characteristics, circumstellar geometry, and kinematics as these sources evolve up and beyond the AGB. I will demonstrate how this extensive sample can be separated into four distinct evolutionary classes: upper AGB, tip of the AGB, just beyond the AGB tip, and post-AGB. By detailing the observable properties that define these transitions, I will show that while large-scale circumstellar environments remain remarkably homogeneous on the upper AGB, they undergo rapid structural changes upon leaving it, a finding that is currently being followed up with detailed radiative transfer modelling.
DAA