Previous abstract Next abstract
Session 72 - Open Clusters.
Display session, Wednesday, January 15
We present initial results for the young open cluster NGC 6834 obtained with the 1-m telescope at Mount Laguna Observatory. We observed this cluster as part of a CCD-photometric survey for Be stars using B,V filters and two narrow-band interference filters at H\alpha and H\alpha continuum. Through a census of Be stars in clusters, where stars are coeval, equidistant, have the same metallicities, and share a common origin, we hope to gain a better understanding of the properties and origins of the still enigmatic Be phenomenon.
Our B,V color-magnitude diagram of NGC 6834 shows an extended blue main sequence widened at fainter magnitudes by field star contamination. Fitting Geneva isochrones with solar metallicity to the cluster population, we find an age of \approx 50 Myr, a mean reddening of E(B-V)\approx 0.7 mag, and a distance modulus of 12.2 mag (i.e. a distance of \approx 2750 pc). Our data reach roughly 4 magnitudes fainter in V than previous photographic or photoelectric studies.
For the detection of Be stars, we use a two-color diagram. The most prominent feature distinguishing Be stars from B stars is their Balmer emission. The (H\alpha\ continuum - H\alpha) index allows us to find stars bright in H\alpha. The (B-V) color index serves to distinguish blue stars from red giants and red supergiants, which also may exhibit H\alpha emission. We find six Be star candidates in NGC 6834, that stand out clearly through their enhanced Balmer emission. Only one was known previously in this cluster. The brightness in H\alpha is well-correlated with reddened (B-V) colors. The relatively small number of Be stars in NGC 6834 is consistent with the young age of the cluster and the spectral type (B5) at the main-sequence turnoff.
Program listing for Wednesday