An ultraviolet, optical and infrared study of Herbig Ae/Be stars

We have selected a list of 45 Herbig Ae/Be-type candidates on the base of their IRAS colors and their spectral types. We propose the presence of a broad infrared excess as a defining criterion for these stars, rather than the detection of circumstellar nebulosity. In this way, our selection also includesmore evolved young stars, that are no longer embedded in their star-forming region. A few objects in our sample are well-known Herbig Ae/Be stars, others are new. New optical and near-infrared photometric observations, as well as ultraviolet ones, are presented. The position of the objects in several color-color diagrams, as well as their de-reddened energy distributions, permit a reliable classification. Three objects probably are binaries with a cool secondary, 9 appear to be related to the Vega-type stars and 33 objects can be classified as genuine Herbig Ae/Be stars. The majority of the Herbig Ae/Be stars have a dusty environment consisting of a distinct hot and cool component. These isolated HerbigAe/Be stars suggest an evolution from embeddedHerbig Ae/Be stars to β Pictoris-like main-sequence stars, an evolution in which planet formation may play an important role.