A comparison between various UV photometric systems for late-type stars.

Ultraviolet absolute photometry and spectrophotometry obtained for late-type stars with the TD1, OAO-2, ANS, and IUE satellites are compared. Strong colour effects are found in the TD1 2740 Å band, and, to a lesser extend, in the OAO-2 2980 Å band. The reason for these effects is believed to be due to red leaks in the sensitivity functions. For the TD1 band at 2365 Å a strong non-linearity at low flux levels is found. The OAO-2 spectrophotometry is found to be significantly influenced by scattered light for late-type stars. The ANS photometry and the IUE LWR spectrophotometry are found to be without large systematic errors. As a corollary the authors give intrinsic UV colours for late-type stars.