Quiescent and active phases in Be stars: A WISE snapshot of young
  galactic open clusters
  Through the modelling of near-infrared photometry of star plus disk systems
with the codes BEDISK/BERAY, we successfully describe the WISE photometric
characteristics of Be stars in five young open clusters, NGC 663, NGC 869, NGC
884, NGC 3766 and NGC 4755, broadly studied in the literature. WISE photometry
allows previously known Be stars to be detected and to find new Be candidates
which could be confirmed spectroscopically. The location of Be stars in the
WISE colour-magnitude diagram, separates them in two groups; active (Be stars
hosting a developed circumstellar disk) and quiescent objects (Be stars in a
diskless phase), and this way, we can explore how often stars are observed in
these different stages. The variability observed in most active variable Be
stars is compatible with a disk dissipation phase. We find that 50 percent of
Be stars in the studied open clusters are in an active phase. We can interpret
this as Be stars having a developed circumstellar disk half of the time. The
location of Be stars with a developed disk in the CMD require mass loss rates
in agreement with values recently reported in the literature. For these
objects, we expect to have a tight relation between the equivalent width of the
H{\alpha} line and the mass of the disk, if the inclination is known. Also,
near-infrared photometry of Be stars in stellar clusters has the potential of
being useful to test whether there is a preferential viewing angle.
