  The technetium-rich (Tc-rich) M stars reported in the literature
(Little-Marenin & Little (1979); Uttenthaler et al. (2013)) 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). Carbon should also be enriched, since it
is dredged up at the same time, after each thermal pulse on the asymptotic
giant branch (AGB). However, these Tc-enriched objects are classified as M
stars, meaning that they neither have any significant zirconium enhancement
(otherwise they would be tagged as S-type stars) nor any large carbon
overabundance (in which case they would be carbon stars). Here we present the
first detailed chemical analysis of a Tc-rich M-type star, namely S Her. We
first confirm the detection of the Tc lines, and then analyze its carbon and
s-process abundances, and draw conclusions on its evolutionary status.
Understanding these Tc-rich M stars is an important step to constrain the
threshold luminosity for the first occurrence of the third dredge-up and the
composition of s-process ejecta during the very first thermal pulses on the
AGB.
