  Nitrogen abundances and carbon isotope ratios (12C/13C) in the atmospheres of
red giants are known to be influenced by dredge-up of H-burning products and
serve as useful probes to study the nature of evolution-induced envelope
mixing. We determined the [N/Fe] and 12C/13C ratios for 239 late-G/early-K
giant stars by applying the spectrum-fitting technique to the 12CN and 13CN
lines in the ~8002-8005A region, with an aim to investigate how these
quantities are related to other similar mixing-affected indicators which were
already reported in our previous work. It was confirmed that [N/Fe] values are
generally supersolar (typically by several tenths dex though widely differ from
star to star), anti-correlated with [C/Fe], and correlated with [Na/Fe], as
expected from theory. As seen from their dependence upon stellar parameters, it
appears that mixing tends to be enhanced with an increase of stellar luminosity
(or mass) and rotational velocity, which is also reasonable from the
theoretical viewpoint. In contrast, the resulting 12C/13C ratios turned out to
be considerably diversified in the range of ~5-50 (with a peak around ~20),
without showing any systematic dependence upon C or N abundance anomalies
caused by the mixing of CN-cycled material. It thus appears that our
understanding on the photospheric 12C/13C ratios in red giants is still
incomplete, for which more observational studies would be required.
