Model of the expansion of H II region RCW 82

This paper aims to resolve the problem of formation of young objects observed in the RCW 82 H {\small II} region. In the framework of a classical trigger model the estimated time of fragmentation is larger than the estimated age of the H {\small II} region. Thus the young objects could not have formed during the dynamical evolution of the H {\small II} region. We propose a new model that helps resolve this problem. This model suggests that the H {\small II} region RCW 82 is embedded in a cloud of limited size that is denser than the surrounding interstellar medium. According to this model, when the ionization–shock front leaves the cloud it causes the formation of an accelerating dense gas shell. In the accelerated shell, the effects of the Rayleigh–Taylor (R-T) instability dominate and the characteristic time of the growth of perturbations with the observed magnitude of about 3 pc is 0.14 Myr, which is less than the estimated age of the H {\small II} region. The total time $t_{\sum }$, which is the sum of the expansion time of the H {\small II} region to the edge of the cloud, the time of the R-T instability growth, and the free fall time, is estimated as $0.44<t_{\sum }<0.78$ Myr. We conclude that the young objects in the H {\small II} region RCW 82 could be formed as a result of the R-T instability with subsequent fragmentation into large-scale condensations.