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Two blue-straggler sequences discovered in globular cluster M30 provide astrong constraint on the formation mechanisms of blue stragglers. We study theformation of the blue-straggler binaries through binary evolution, and findthat binary evolution can contribute to the blue stragglers in both of thesequences. Whether a blue straggler is located in the blue sequence or redsequence depends on the contribution of the mass donor to the total luminosityof the binary, which is generally observed as a single star in globularclusters. The blue stragglers in the blue sequence have a cool white-dwarfcompanion, while the majority ($\sim 60\%$) of the objects in the red sequenceare the binaries that are still experiencing mass transfer, but there are alsosome objects that the donors have just finished the mass transfer (thestripped-core stars, $\sim 10\%$) or the blue stragglers (the accretors) haveevolved away from the blue sequence ($\sim 30\%$). Meanwhile, W UMa contactbinaries found in both sequences may be explained by various mass ratios, thatis, W UMa contact binaries in the red sequence have two components withcomparable masses (e.g. mass ratio $q\sim$ 0.3-1.0), while those in the bluesequence have low mass ratio (e.g. $q<$ 0.3). However, the fraction of bluesequence in M30 cannot be reproduced by binary population synthesis if weassumed the initial parameters of a binary sample to be the same as that of thefield. This possible indicates that dynamical effects on binary systems is veryimportant in globular clusters.

Contribution of primordial binary evolution to the two blue-straggler sequences in globular cluster M30