  The J-type carbon (J)-stars constitute 10-15% of the observed carbon stars in
both our Galaxy and the Large Magellanic Cloud (LMC). They are characterized by
strong 13C absorption bands with low 12C/13C ratios along with other chemical
signatures peculiar for typical carbon stars, e.g. a lack of s-process
enhancement. Most of the J-stars are dimmer than the N-type carbon stars some
of which, by hot-bottom burning, make 13C only in a narrow range of masses. We
investigate a binary-star formation channel for J-stars involving re-accretion
of carbon-rich nova ejecta on main-sequence companions to low-mass
carbon-oxygen white-dwarfs. The subsequent evolution of the companion stars in
such systems is studied with a rapid binary evolutionary code to predict
chemical signatures of nova pollution in systems which merge into giant single
stars. A detailed population synthesis study is performed to estimate the
number of these mergers and compare their properties with observed J-stars. Our
results predict that such nova polluted mergers evolve with low luminosities as
well as low 12C/13C ratios like the majority of observed J-stars (e.g. in the
LMC) but cannot account for the observed fraction of J-stars in existing
surveys of carbon stars.
