N-type carbon stars and the 3-alpha process.

High-dispersion yellow-red spectra of eight representative N-type carbon stars have been matched by Minneart model synthesis. CN, C2, and Fe line strengths imply high abundances of free carbon, C- 0, such that N-star surface carbon must originate from 3-o He- shell burning, rather than from CNO equilibrium processes. CN/C2 ratios ranging from 4 to 200 imply values of log (C - 0)/H from -2.7 to -4.5; these lead to ClO ratios from 2.9 to 1.033, if the oxygen abundances are solar. Nitrogen abundances for these stars are also essentially solar, with a mean value log (N/H) = - 4.10 0.18, also ruling out substantial contributions from C NO processing. Values of the '2C/'3C ratio range from 3.5 to > 25. Zr/Ti ratios are a factor of 2 to 10 greater than solar, similar to the S stars. Ba is enriched only in some high Zr stars. Rareearth abundances are subject to severe error. Lithium abundances range from the meteoritic to below solar. The range of log g is -0.3 to 1.7. Excitation temperatures, both atomic and and molecular, are between 2500 K and 3150 K. Microturbulent velocities are in most cases near 6 km sec-1. Relations to other red-giant stars are considered.