Spectroscopy of Supergiants with Infrared Excess: Results of 1998–2018

Abstract

The results of our second stage of the detailed spectroscopy of peculiar supergiants identified with galactic infrared sources, performed at the 6-meter BTA telescope are summarized. The main aspect of the program is a search for the evolutionary variations in the chemical composition of stars, past the AGB stage and the TDU, as well as an analysis of spectral manifestations of kinematic processes in their extended, often unstable, atmospheres and in the envelopes. The most significant result is detection of the s-process element excesses in seven single post-AGB stars, which confirms the theory of evolution of this type of stars. In three of these stars we for the first time discovered the ejection of the s-process heavy metals to the circumstellar envelopes. A Li excess was found in the atmospheres of peculiar supergiants V2324 Cyg and V4334 Sgr. The results of investigation of the kinematical parameters of atmospheres and envelopes will clarify the equilibrium of matter produced by stars in the AGB and post-AGB stages and delivered to the interstellar medium.

Long-term photospheric instabilities and envelopes dynamics in the post-AGB binary system 89 Herculis

“…These kind of splitting have already been observed in evolved stars, although their temporal variability has never been completely investigated. In the already mentioned case of the hypergiant ρ Cas, the variability observed in the splitting of the strong Ba ii 6141 Å line was associated with the one decade cadence kinematic instabilities of the upper atmospheric layers (Klochkova 2019). In our case we do not see any correlation between splitting variability of s-process elements and the long-term changes of the star.…”

“…The large variability often observed in such profiles (e.g. Klochkova 2019, and references therein), allows us to investigate the instability of the extended atmosphere of evolved stars, characterized by expanding shells of ejected mass and layers falling back on the stellar surface. These processes lead to an effective transport into the envelope of matter synthesized in the previous stage of stellar evolution.…”

Post-AGB Stars as Tracers of AGB Nucleosynthesis: An Update

“…The first studies focusing on the s-process elemental abundances started with individual studies of isolated Galactic objects (e.g., [51,52]). Many authors followed, and overview papers on the results of these abundance determinations of Galactic sources can be found in, e.g., [19,23,[53][54][55] and references therein.…”