Speaker
Description
The technetium(Tc) -rich M stars reported in the literature
(Little-Marenin & Little 1979; Uttenthaler et al. 2013; Shetye et al. 2022) are
puzzling objects since no isotope of technetium has a half-life longer than a few
million years, and 99Tc, the longest-lived isotope along the s-process path, is
expected to be detected only in thermally-pulsing stars enriched with other
s-process elements (like zirconium). The anomaly deepens as carbon
enrichment is anticipated in tandem with zirconium, following each thermal
pulse on the asymptotic giant branch (AGB). Surprisingly, the Tc-rich M stars
lack significant zirconium enhancement (which would categorise them as
S-type stars) and display no substantial carbon overabundance (which would
label them as carbon stars).
In my talk, I'll present a systematic high-resolution study of a large sample of
Tc-rich M stars. I'll delve into the spectral properties of these stars, and its
comparison with those of Tc-rich S stars. Additionally, I'll present their s-process
element abundance analysis, accompanied by a comparison of their location
on the HR diagram with Tc-rich S-type stars. Lastly, I will discuss the role of
Tc-rich M stars as the potential tracer of the onset of the third dredge-up.
