New high-resolution 1.0 - 3.4 pm spectra of carbon-rich Wolf-Rayet stars (W C ) are presented. The line identifications are discussed and some 20 new identifications are given, due to neutral helium and ions of helium, carbon, oxygen and magnesium, notably the strong C IV 4p-4s doublet near 1.435 pm. It is shown that the infrared features are sufficient to define the subtypes, and that the optical classification lines refer to unrelated parameters: the ionization and the composition of the wind.
Recombination lines are used to derive the C/H e ratio in six W C and one W O stars. The validity of the assumptions is examined: the data are shown to be consistent with the lines being optically thin and formed by recombination; the increase in free-free optical depth with wavelength is used to estimate the effect of the wind stratification. The derived C/H e ratios for W C stars are higher for earlier subtypes, they are much in excess over the solar value, and agree well with the results of other analyses. For the W O star, the C/H e ratio is even higher, but lower than predicted by evolutionary models.
Using new high-resolution spectra, the He I 2p-2s triplet and singlet profiles near1.083 and 2.058 pm are analyzed, and shown to yield better estimates of the wind expansion velocity (uoo) than conventional methods (based on the violet edge of ultraviolet resonance lines, or the width of optical emission lines). It is demonstrated that the velocities from the absorption trough of ultraviolet resonance P Cygni lines are contaminated by the companion O-star wind in W R +O binaries. The infrared He I profiles are fitted to derive v^ in a sample of 41 galactic W R stars of all subtypes. The derived Uqo tend to be higher in earlier subtypes. In general they are lower than those from the other methods, implying that the previous estimates of the mass-loss rates are also too high.
The presence of emission subpeaks on the infrared He I lines is noted for the first time. These are widespread among W R stars, regardless of the subtype or the presence of an O-star companion. The subpeaks are believed not to vary with time and are suggested to be the signature of asymmetries in the wind.