Gravitational instability of non-isothermal filamentary molecular
  clouds, in presence of external pressure
  Filamentary molecular clouds are omnipresent in the cold interstellar medium.
Observational evidences show that the non-isothermal equations of state
describe the filaments properties better than the isothermal one. In this paper
we use the logatropic and the polytropic equations of state to study the
gravitational instability of the pressure-confined filaments in presence of a
uniform axial magnetic field. To fully explore the parameter space we carry out
very large surveys of stability analysis that cover filaments with different
radii in various magnetic fields. Our results show that for all the equations
of state the instability of thinner filaments is more sensitive to the magnetic
field variations than the thicker ones. Moreover, for all the equations of
state, an intermediate magnetic field can entirely stabilize the thinner
filaments. Albeit for the thicker ones this effect is suppressed for the
magnetic field stronger than B ' 70 micro G.
