Thermal instability in interstellar clouds

Thermal instability of magnetized interstellar atomic clouds is investigated with the method of small perturbations. The dispersion relation is obtained for model heating and cooling functions as well as for radiative recombinations and ionization by cosmic rays. The dispersion relation is solved numerically with Bairstow method. It was shown that for model cooling function $\Lambda \propto T^\zeta $ isobaric instability develops for $\zeta <0.2$. In the cold diffuse clouds can develop instabilities of slow magnetosonic waves for $\zeta >1$. Also instability of standing waves can arise at $0.2<\zeta < 1$. Applications to the cold neutral medium and warm neutral medium are considered.