HERMES is the high resolution optical spectrograph of the 1.2m Mercator telescope at the Roque de los Muchachos observatory at La Palma, Spain. After commissioning we started a long-term monitoring programme of evolved stars and focused on detecting and/or monitoring binaries with an evolved stellar component. The latter is either a post-AGB star or a white dwarf. Now, 15 years later I will...
With about 100 Galactic candidates detected, Post-Asymptotic Giant Branch (post-AGB) binaries are now understood to be fairly commonly formed systems at the end of stellar evolution, displaying clear signs of ongoing re-accretion from their ubiquitous circumbinary disks. For $\sim 35$ of these systems, long-term, high-resolution spectral monitoring of the $\mathrm{H_\alpha}$ line has revealed...
Ongoing improvements in the sensitivity of sub-mm- and mm-range interferometers and single-dish radio telescopes allow the more and more detailed study of AGB and post-AGB objects in molecular species other than $^{12}$CO and $^{13}$CO. With a new update introduced in the modelling tool SHAPE+shapemol, we can now create morpho-kinematical models to reproduce observations of these shells in up...
Post-AGB stars play a significant role in enriching and advancing the chemical complexity of the Universe. During the late stages of low-to-intermediate mass stellar evolution, substantial outflows of dust and gas are injected into the interstellar medium (ISM). Post-AGB stars undergo significant intrinsic changes, and, in a notable proportion, they also experience changes induced by...
Stellar evolution and nucleosynthesis models are fundamental tools to derive parameters of stars from elemental atomic and isotopic abundance ratios. For evolved stars, the C/O/N elemental ratios and the $^{12}$C/$^{13}$C and $^{16}$O/$^{17}$O/$^{18}$O isotopic ratios provide very significant constraints to the otherwise elusive initial mass of the stars. In the case of post-AGB sources, the...
Planetary nebulae (PNe) are the ejected gas and dust shells of Asymptotic Giant Branch (AGB) stars. We present an abundance comparison between PNe and their progenitors to disclose their similarities and differences since such a comparison has been rarely, and not recently, done in the Milky Way. While we expected similarities in most of the alpha-element distributions across the two...
Low-mass stars lose a significant fraction of their mass during the final stages of the asymptotic giant branch (AGB) phase, resulting in the production of a substantial mass fraction of dust. The mass loss process influences the timescales of the transition from the AGB to the planetary nebulae (PNe) phase, while the residual dust contributes to the spectral energy distribution of the PNe....
The events that occur during the proto-planetary nebula (PPN) inter-phase are among the most stunning phenomena taking place during the evolution of solar and intermediate mass stars. PPNe comprise a dense circumstellar envelope that hide hot central stellar objects, which are frequently white dwarfs. PPNe usually display high velocity bipolar outflows that form close to the central stellar...
