Searching for Be Stars in the Open Clusters with PTF/iPTF. I. Cluster Sample and Be Star Candidates

Abstract

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. Among 104 open clusters, we identified 96 Be star candidates in 32 clusters; 11 of our candidates have been reported in previous studies. 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. Spatial distribution of Be star candidates with different ages implies that they do not form preferentially in the central regions. Furthermore, 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. Finally, among 96 Be candidates, we discovered that one Be star candidate FSR 0904-1 exhibits long-term variability on the timescale of ∼2000 days with an amplitude of 0.2-0.3 mag, indicating a long timescale of disk evolution.

A Comprehensive Study of the Young Cluster IRAS 05100+3723: Properties, Surrounding Interstellar Matter, and Associated Star Formation

“…We thus considered the radius of the cluster to be 2.5 arcmin. The estimated radius is in agreement with the cluster size of 5.2 arcmin (or radius of 2.6 arcmin) reported in Yu et al (2018). A circle of thus estimated radius is also over plotted on the SSDM, which is in good agreement with the size of the SSDM map.…”

“…Figure 1 shows the WISE 12 µm image around the cluster over 30×30 arcmin 2 area as well as the central 5×5 arcmin 2 area in the near-infrared (NIR) H-band from the UKIDSS-GPS (Lucas et al 2008) wherein the cluster is clearly visible. There are several shallow optical and infrared studies on the cluster suggesting that the cluster is located at a distance between 2.2 and 6.8 kpc and its age lies somewhere between 1 and 25 Myr (Lahulla 1985;Hunter & Massey 1990;Kharchenko et al 2013;Yu et al 2018). To date, the most detailed work on the cluster has been carried out by Borissova et al (2003) using NIR observations.…”

“…This makes the cluster one of the potential young massive clusters in our Galaxy such as Orion Nebula Cluster (ONC, mass ∼2000 M and age ∼3 Myr, see Hillenbrand 1997;Da Rio et al 2010), albeit at a farther distance. Borissova et al (2003) estimated the cluster radius to be 1.5 arcmin while Yu et al (2018) reported the cluster radius to be 2.5 arcmin.…”

Identification of emission-line stars in transition phase from pre-main sequence to main sequence

“…Majority of these known CBe stars (1991 stars) are taken from Chen et al (2016b) and Neiner et al (2011). In addition, we also obtained 176 CBe stars from Fabregat et al (1996), Yudin (2001), Chauville et al (2001), Levenhagen & Leister (2006), Silaj et al (2010), Draper et al (2014), Raddi et al (2015), Lin et al (2015), Chojnowski et al (2015), Gkouvelis et al (2016), Zorec et al (2016), Yu et al (2018 and Dimitrov et al (2018).…”

HO Puppis: Not a Be Star, but a Newly Confirmed IW And-type Star

“…Be phenomena are the photometric and spectroscopic variability seen in the main-sequence luminous rapid rotators, known as Be stars, with a luminosity class III−V. In recent years, we have studied the evolutionary effect on the formation of Be stars in open clusters (Yu et al 2015(Yu et al , 2016(Yu et al , 2018 using the Palomar Transient Factory (Law et al 2009) and the intermediate Palomar Transient Factory (iPTF; Kulkarni 2013). The Zwicky Transient Facility (ZTF; Bellm et al 2019;Graham et al 2019;Masci et al 2019) came after iPTF, and its improved data can extend our investigation on the variability of Be stars (Ngeow et al 2019), especially for the Be stars and Be-star candidates at the faint end (m > 13 mag), which were largely excluded from previous works (e.g., in Labadie- Bartz et al 2017).…”