Discovery of enrichment of the envelopes
of post-AGB stars with heavy metals

    High spectral resolution echelle spectroscopy of supergiants at the post-ABG stage resulted in the formation of a sample of these objects possessing a high infrared excess, an emission at 21 μm, and also large overabundances of carbon and heavy metals, synthesized by the s-process at the preceding AGB stage.
    As a result of the spectroscopic monitoring carried out at the 6-m BTA telescope, a previously unknown (for this evolutionary stage) phenomenon was discovered in the optical spectra of selected objects of this sample - an asymmetry of the metal lines, to the extent of splitting of the strongest low-excitation absorption lines. The effect is strongest in the most evolved, high-latitude supergiant V5112 Sgr=IRAS19500-1709, which has an extended structured envelope (Figs.1 and 2). In the optical spectrum of this object, the BaII ion lines are split into three components (Figs.3 and 4).
    An analysis of the velocity field in the extended atmosphere and envelope of V5112 Sgr resulted in a conclusion that the short-wavelength components of the split BaII absorptions are formed in the structured circumstellar envelope. Thus, we discovered for the first time the enrichment of the stellar envelope with heavy metals produced at the AGB stage.
Published:
V.G.Klochkova. Detection of heavy-metal lines in the spectrum of the circumstellar envelope of a post-AGB star. Astronomy Letters, 2009, 35, No.7, pp.457-465.
V.G.Klochkova. High-latitude supergiant V5112 Sgr: Enrichment of the envelope with heavy s-process metals. Astronomy Letters, 2013, 39, No.11, pp.765-775

Fig.3. The BaII 4554 A line, split into 3 components, in the spectrum of V5112Sgr. The FeII 4556 À line with a similar intensity is not split

Fig.4. The variability of the profile of the split BaII 4934 Å line in the spectrum of V5112Sgr. The vertical arrows show the envelope components. The dashed line denotes the systemic velocity