P.-C. Yu (IANCU); C.-H. Yu (IANCU); C.-D. Lee (IANCU); C. -C. Lin (MPIA); C.-H. Hsia (MUST); C.-K.Chang (IANCU); I.-C. Chen (IANCU); C.-C. Ngeow (IANCU); W.-H. Ip (IANCU); W.-P. Chen (IANCU); PTF/iPTF Team (Caltech)
We conducted a search for Be star candidates in open clusters using Hα imaging photometry of the Palomar Transient Factory Survey to investigate some connections among Be star phenomena, cluster environments, and ages. Stellar members of clusters were identified by spatial distributions, near-infrared magnitudes and colors, and by proper motions. We identified 96 Be star candidates in 32 clusters among 104 open clusters. We found that the clusters with age 7.5 < log(t(year)) ≤ 8.5 tend to have more Be star candidates; there is about a 40% occurrence rate within this age bin. The clusters in this age bin also tend to have a higher Be fraction N(Be)/N(Be+B-type). These results suggest that the environments of young and intermediate clusters are favorable to the formation of Be phenomena. Moreover, we showed that the mid-infrared (MIR) colors of the Be star candidates are similar to known Be stars, which could be caused by free–free emission or bound-free emission. Some Be star candidates might have no circumstellar dust according to their MIR colors.