The YY Orionis stars are a subclass of the T Tauri stars which show in their spectra evidence for infailing envelopes. They are interpreted as protostars in the final stages of their hydrodynamical evolution (Walker 1972, Appenzeller and Wolf 1977, Wolf et al. 1977).
To get more information about the behaviour of these highly variable stars simultaneous spectroscopic and photoelectric (UBV) observations have been carried out in July 1977 at the ESO observatory at La Silla. Such observations of YY Orionis stars have never been done before.
The most frequently observed star during our run was the bright YY Orionis star S CrA. The observational material is still under evaluation and therefore only some preliminary results are presented here. A more extended description and discussion of the observations will be published elsewhere (Mundt and Wolf, 1977).