| dc.description.abstract | Herbig Ae/Be stars are intermediate-mass young stars. The fast evolution in the premain sequence phase causes a much less number of-and hence relatively poorer knowledge toward|Herbig Ae/Be stars than that of low-mass young stars. In addition to the emission lines in the spectra, the Herbig Ae/Be stars are characterized by infrared excess. We utilized the 2MASS database to identify Herbig Ae/Be candidates in open clusters, and carried out low-dispersed spectroscopic observations to study the nature of these candidate stars. Out of 11 observed sources, we have found 1 Herbig Ae star in the open cluster Dolidze 16, and in other clusters 5 extremely red low-mass young stars. Most notable is the star VES888 in NGC1857. Our optical photometry suggests that the age of the cluster is about 108:35 years, too old to host a Herbig Ae/Be star. It turns out that VES888 is a classical Be star, which as a group is characterized by rapid rotation close to break-up and emission lines in their spectra. Typically however the classical Be stars are lacking in infrared excess, hence making VES888 a rare case. VES888 is near the main sequence turn-off, whereas two other classical Be stars in the cluster, with much weaker IR excess, are both in earlier evolutionary stages. The infrared excess in classical Be stars, while in most cases arising from thermal free-free emission, seems to be escalated when the star is evolving off the main sequence to pu up the stellar envelope, in a disk-like geometry because of the rapid rotation, in which the dust grains condense to reprocess stellar light to be responsible for the strong circumstellar infrared emission. | en_US |