first tens Myr of their lives through several evolutionary stages, from the stage when young stars clumps are completely obscured by their dusty gas cocoons to the stage of a young star cluster with no evidence of H[ii]{} [@lada2003]. @whitmore2011 developed the evolutionary classification scheme of star clusters based on the [*Hubble Space Telescope (HST)*]{} observations of M83. Star clusters become visible in optical bands since about 1 Myr (’obscured clusters’). Ionized gas stays spatially coincident with cluster stars during $1-4$ Myr (’emerging clusters’). Clusters with ages $\approx4-5$ Myr have a small H[ii]{} bubble with radius of $7-20$ pc (’very young clusters’), surrounding the cluster. Star clusters with ages $\ge 5$ Myr have a larger ionized gas bubble surrounding the cluster (’young clusters’). H[ii]{} bubbles are dissolved around star formation regions older than $8-10$ Myr. From the age $>10$ Myr, we observe blue, but redden ageing star clusters without H$\alpha$ emission [’intermediate-age clusters’ by @whitmore2011]. These clusters are free from dust.

Thus, the dependence between separations of star clusters from the nearest H$\alpha$ source and $U-B$ colour index (age) of a star cluster can be used to directly measure the velocity of star formation propagation.

Search and selection of star 