  High-resolution infrared spectra (R=50,000) have been obtained for twelve
red-giant members of the LMC with the Gemini South 8.3-meter telescope plus
Phoenix spectrometer. Quantitative chemical abundances of carbon-12, carbon-13,
nitrogen-14, and oxygen-16 were derived from molecular lines of CO, CN, and OH,
while sodium, scandium, titanium, and iron abundances were derived from neutral
atomic lines. The LMC giants have masses from about 1 to 4 solar masses and
span a metallicity range from [Fe/H]= -1.1 to -0.3. The program red giants all
show evidence of first dredge-up mixing, with low 12C/13C ratios, and low 12C
correlated with high 14N abundances. Comparisons of the oxygen-to-iron ratios
in the LMC and the Galaxy indicate that the trend of [O/Fe] versus [Fe/H] in
the LMC falls about 0.2 dex below the Galactic trend. Such an offset can be
modeled as due to an overall lower rate of supernovae per unit mass in the LMC
relative to the Galaxy, as well as a slightly lower ratio of supernovae of type
II to supernovae of type Ia.
