Ultraviolet photometry from the Orbiting Astronomical Observatory. V. The helium-weak stars

Ultraviolet filter photometry with the Wisconsin Experiment Package aboard OAO-2 has been carried out for the helium-weak stars 3 Cen A, 3 Sco, RD 144334, RD 21699, RD 144844, a Scl, RR 8535, RR 8770, and RD 144661. The flux distribution is compared with that of B3 to B8 main-sequence and giant stars in terms of color-color diagrams. After taking into consideration line blocking shortward of 2800 A due to lines of P ii, Ga ii, Si ii, Si iii, Ti ii, and Sr ii, we find that most of the helium-weak stars have normal fluxes in good agreement with their ground-based colors. Rowever, it is difficult to consider RR 8535, RR 8770, and RD 144661 as having normal flux distributions and they may be brighter than normal at 3320 A. The star, a Scl, is a photometric variable. It is suggested that variations in the strengths of lines of Ti ii, Cr ii, and Sr ii around 2400 A are responsible for this phenomenon, causing a redistribution of flux between the far-ultraviolet and visual regions. The flux distribution indicates an effective temperature about 1500 K higher than previously determined.