Extrinsically metal-poor stars: photospheric chemical depletion in post-AGB/post-RGB stars in the Large Magellanic Cloud

In this study, we use high-resolution optical spectra from the VLT + UVES to carry out a detailed stellar parameter and chemical abundance analysis for three newly identified depleted LMCpost-AGB/dusty post-RGB stars with circumstellar discs. Previously, only four luminous post-AGB stars in the Large Magellanic Cloud (LMC) have been observed to show signatures of chemical depletion. We find that the luminosities of the new depleted objects presented in this study are lower (1800 less than or similar to L/L-circle dot less than or similar to 3300) than that of the previously known LMC depleted post-AGB stars (3000 less than or similar to L/L-circle dot less than or similar to 6500). This shows that chemical depletion is not only active in luminous post-AGB stars but also in stars with lower luminosities that have evolved-off lower on the AGB or evolved-off the RGB. Additionally, we compare the chemical depletion patterns of the LMC objects to their Galactic counterparts. We find a similar spread in the efficiency of depletion in both galaxies implying that the efficiency of photospheric depletion is independent of the initial metallicity of the host galaxy. While the spectral energy distributions of depleted post-AGB stars in the LMC and our Galaxy point to the presence of a likely circumstellar disc, we find that the stable circumstellar disc is needed but not a sufficient condition for acquiring the photospheric depletion abundance patterns. The efficiency of chemical depletion is complexly dependent on a suite of factors such as the effective temperature, luminosity, and the orbital properties of the binary systems.