GS242-03+37: a lucky survivor in the galactic gravitational field
  HI shells and supershells, found in discs of many galaxies including our own,
are formed by the activity of young and massive stars (supernova explosions and
stellar winds), but the formation of these structures may be linked to other
energetic events, such as interactions of high-velocity clouds with the
galactic disc. The larger structures in particular significantly influence
their surroundings; their walls are often places where molecular clouds reside
and where star formation happens. We explore the HI supershell GS242-03+37, a
large structure in the outer Milky Way. Its size and position make it a good
case for studying the effects of large shells on their surrounding. We perform
numerical simulations of the structure with the simplified hydrodynamical code
RING, which uses the thin-shell approximation. The best fit is found by a
comparison with the HI data and then we compare our model with the distribution
of star clusters near this supershell. The best model of GS242-03+37 requires,
contrary to previous estimates, a relatively low amount of energy, and it has
an old age of $\sim$ 100 Myr. We also find that the distribution of young star
clusters (with ages $<$ 120 Myr) is correlated with walls of the supershell,
while the distribution of older clusters is not. Clusters that have the highest
probability of being born in the wall of the supershell show an age sequence
along the wall. GS242-03+37 is a relatively old structure, shaped by the
differential rotation, and its wall is a birthplace of several star clusters.
The star formation started at a time when the supershell was not already
supersonically expanding; it was a result of the density increase due to the
galactic shear and oscillations perpendicular to the disc of the Milky Way.
