Observations of the C III lambda 8500 (3s1S-3p1P) line in O and Of stars.

Measurements from coude infrared image-tube spectra of the equivalent widths of the C iii A8500 (3s1S-3p1P0), Heii x10124 (n = 4- n = 5), and hydrogen P8 lines have been made for several 0 and Of stars, and are presented here. An attempt to measure the C ni xx9701-15 complex (3p3P0-3d3D) was thwarted by interference from telluric H20 absorption. The C iii x8500 line strengths provide useful constraints on possible theoretical models, and suggest, on the basis of the calculations of Nussbaumer (1971), that the C iii x5696 (3p2P0-3d'D) and x8500 lines are formed in relatively extended atmospheres, with a dilution factor 0.1. Key words: Of stars - stellar spectra - stellar atmospheres