The Keenan and Wing bands in S stars

New observations of the near infrared spectra of S stars are presented as part of a survey of the unidentified Keenan and Wing bands. Bandhead wavelengths accurate to 0.5 Å are presented. A new band is found at 9014 Å. The bands are not present in normal M giants and dwarfs. Laboratory spectroscopy of heavy element oxides is reported. Several new identifications are proposed. The 10 300 Å Wing band is identified with the Δυ = – 1 sequence of the ZrO 9300 Å Δυ = 0 bands. The |ZrO \,B¹∏-A¹Δ (Δ υ = 0)| system may be responsible for either the 9736 Å or the 10 515 Å Wing bands. Two new bands in the near infrared at 8219 and 8235 Å are provided by CeO. A new band with heads at 7503 and 7509 Å in a spectrum of R And is tentatively attributed to YS. A band at 8268 Å in M stars is the TiO δ(2–1) head. The 8610 Å Keenan band is not due to CrH. Potential carriers of the Keenan and Wing bands are reviewed. It is suggested that the heavy element sulphides and, perhaps, chlorides are leading candidates. Indentification of YS in R And may provide the first evidence for these sulphides. ZrS is a leading candidate for which laboratory spectroscopy is needed. The following molecules have been searched for but not seen in cool S stars: TaO, NbO, PrO, LaS, LaF and ZrCl.