Spectroscopic studies of Wolf-Rayet stars. VI. Optical spectrophotometry of near-infrared emission lines in some Galactic stars

We present spectroscopy of 47 WN stars and 36 WC stars in our Galaxy in the near-infrared. In the WN types, the strongest lines are due to He II transitions and N IV at lambda 7115. In WC types, the strongest lines are due to C III, particularly at lambda 9711; C II transitions, the strongest at lambda 7236, and C IV lines, particularly at lambda 7726, are also found. It is a relatively easy procedure to determine the W-R class from this wavelength region; similarly, the distinction between WNE ("early") and WNL ("late"), and between WCE ("early") and WCL ("late") may also be made, although numerical W-R subtypes cannot easily be determined from this near-infrared region. A comparison of line ratios of the various ions found in W-R stars suggests that it is only the optical N IV lambda 4057 and C III lambda 5696 transitions which do not behave in a "well-understood" manner; curiously enough, it is just these lines that play an important role in the traditional numerical subtype definitions.