Photometric monitoring of early type emission line stars

A programme of simultaneous optical (UBVRI) and infrared (JHKL MNQ) photometry of early type, emission line, stars is described. Particular emphasis is placed on observations of suspected pre-main-sequence objects such as Herbig Ae/Be stars. The observations, together with data from the IRAS point source catalogue, are analysed to probe the circumstellar environments of these objects and to determine the extent and causes of optical variability in such stars. It was found that many of these stars are associated with warm circumstellar dust and that the mean temperature of that dust is higher than the characteristic temperature of dust associated with T Tauri stars. It is shown that many of the stars in the programme display variablity at optical and infrared wavelengths, but that no single mechanism can account for the variability. The main variability mechanisms found are obscuration by circumstellar dust and changes in the underlying star. In some cases more than one mechanism operates at different times in a single star. It is also shown that the class of objects described as Herbig Ae/Be stars is very heterogeneous and that trends of variability range with spectral type reported by other authors may be illusory. Some unusual stars, including V644 Cen and HD97048 are identified and examined in detail. Suggestions are made for future work A brief spectrophometric survey of similar stars is also reported