From the Asymptotic Giant Branch to the Planetary Nebula phase. A study of the mass-loss and dust production processes

The asymptotic giant branch (AGB) phase, undergone by low- and intermediate-mass stars (LIMS), plays a crucial role in galactic dust production, though mechanisms that remain poorly understood. The post-AGB and planetary nebulae (PNe) phases provide valuable insights into LIMS evolution, as their spectra contain chemical signatures that trace nucleosynthesis and dust production, without the blending effects found in AGB spectra. To enhance our understanding of LIMS, we selected a sample of 44 post-AGB stars and 9 PNe from the Magellanic Clouds and the Milky Way. These objects were characterized through SED analysis by collecting and analyzing relevant observational data, including chemical abundances, photometry, and spectra, spanning from ultraviolet to infrared wavelengths. Our analysis enabled us to determine the amount of dust and gas surrounding each central star and estimate the progenitor mass for all sources. This was achieved by specifically extending the ATON stellar evolutionary tracks to the PN phase for this study. Furthermore, by linking these properties to the previous AGB phase, we were able to test existing theoretical evolutionary models for LIMS and recommend revisions where necessary. Specifically we suggest that the mass-loss rate at the tip of the AGB phase for metal-poor low-mass carbon stars must be $3-4\times 10^{-5}~{\rm M}_{\odot}/$yr, which is 3--4 times higher than the typical values reported in the literature. Furthermore, contrary to previous findings, we propose that the dust observed around post-AGB stars was released when the central star's effective temperature increased to approximately 3500--4000\,K. Additionally, we observed a positive correlation between the progenitor's mass and the amount of dust in the post-AGB phase, and a similar trend for PNe, although modulated by the central star's effective temperature, which may influence dust destruction. In contrast, the gas content in PNe was found to be inversely proportional to the progenitor’s mass. Additionally, we found that low-metallicity environments result in higher dust production in carbon-rich stars and lower amounts in oxygen-rich stars. Massive carbon stars ($1.5\rm{M}_{\odot} \lesssim \rm{M} \lesssim 2.5 \rm{M}_{\odot}$) were found to have dust layers closer to the central star compared to lower-mass carbon stars. Future observations with the James Webb Space Telescope and Gaia astrometric data will expand our sample and provide more precise insights into the dust contributions from these sources.