Gaia EDR3 data of post-AGB stars with overabundance of s-process elements and their evolutionary status and binarity

Abstract: Recently Kamath et al. (2021) analysed Gaia EDR3 data of eighteen post-AGB supergiants with overabundance of s-process elements. For some of these stars in their sample they find unusually very low absolute luminosities which is not in agreement with the s-process nucleosynthesis on the AGB stage of evolution. It appears that they have not taken into account the RUWE values of these stars. I have taken a look at the RUWE values of these eighteen post-AGB stars with over abundance of s-process elements. Of the eighteen stars thirteen have RUWE values much greater than 1.4 and hence their distances (absolute luminosities) are not reliable. As per the study of Stassun and Torres (2021) stars with Gaia EDR3 RUWE values greater than 1.4 are most likely unresolved binaries in Gaia data base. Thus some of the s-process rich post-AGB stars are most likely contain unresolved low-mass binary companions. Only five stars (IRAS 07134+1005, IRAS 08143-4406, IRAS 12360-5740, IRAS 19500-1709 and IRAS 22272+5435) of these eighteen s-process rich stars have accurate Gaia EDR3 parallaxes and RUWE values less than 1.4 and their absolute luminosities are in agreement with the post-AGB evolutionary tracks.