I have determined physical parameters (interstellar reddening, distance and age) for 3 young open clusters: h Persei, Persei and NGC 1893, studying their massive star populations and formation epochs.
I have presented photometric data for 350 stars in the double open cluster h and Persei. For both clusters the I determine and . However, I find a small difference in their ages. Most stars in h Persei follow the isochrone while some of the massive stars seem younger. The stars in Persei would fit better isochrones in the range.
I have presented photometric data for 114 stars in NGC 1893. For this cluster, I find , a distance rather larger than the traditional value for Aur OB2, but consistent with recent determinations. I have obtained spectroscopy for photometrically peculiar stars in NGC 1893. Among them, I find six emission-line stars, identified as pre-main-sequence (PMS) stars with spectral types between B0 and late-F. For 2 of these stars, the derived spectral types indicate that they are very massive Herbig Be stars. On the other hand, one other B-type emission line star looks like a classical Be star.
The presence of massive PMS stars in NGC 1893 suggests that many other fainter PMS stars could be present. A spectroscopic study of objects not falling on the cluster main sequence found several objects whose spectral types and colors suggested that they could be absorption-line PMS stars. While many early and intermediate B-type stars are settled on to the main sequence, the detection of early-B PMS stars indicates that star formation continues after several hundred thousand years in NGC 1893.
This work has produced a list of new uvby standard stars for the study of moderately reddened clusters and has shown that the combination of Strömgren photometry and low resolution spectroscopy is a powerful tool for the detection of PMS population in young open clusters.