Studying the interstellar medium to look for relics of triggered star
  formation among stellar clusters
  Evidence of triggered star formation at large spatial scales involving
stellar clusters is scarce. We investigate a Galactic region (l=130.0, b=0.35)
populated by several open stellar clusters that according to the last GAIA data
release, are located at a distance of about 2.9 kpc. By analyzing the
interstellar medium (ISM) at infrared, centimeter, and millimeter wavelengths
towards this group of clusters we discovered a shell of material of about 2
degree in size at the same distance. We suggest that the shell, mainly observed
at 12 um and in the Hi emission at 21 cm, was generated by the action of
massive stars belonging to clusters Berkeley 7 and UBC 414, that lie at its
center. Five clusters (MWSC0152, Czernik 6, Czernik 7, Berkeley 6, NGC 663, and
NGC 654) lie at the border of this shell. From the comparison between the
dynamical time of the discovered Hi shell and the analysis of the ages of
stellar populations in these clusters, we conclude that the expansion of the
shell could have triggered in the past the formation of stars in some of them.
We point out that in order to find physical evidence supporting a genetic
connection between stellar clusters, it is necessary not only to study the
individual clusters and their stellar populations, but also to investigate
their surrounding ISM at a large spatial scale.
