The origin of the two populations of blue stragglers in M30
  We analyze the position of the two populations of blue stragglers in the
globular cluster M30 in the Hertzsprung-Russell diagram. Both populations of
blue stragglers are brighter than the cluster's turn-off, but one population
(the blue blue-stragglers) align along the zero-age main-sequence whereas the
(red) population is elevated in brightness (or colour) by $\sim 0.75$ mag.
Based on stellar evolution and merger simulations we argue that the red
population, which composes about 40\% of the blue stragglers in M 30, is formed
at a constant rate of $\sim 2.8$ blue stragglers per Gyr over the last $\sim
10$ Gyr. The blue population is formed in a burst that started $\sim 3.2$ Gyr
ago at a peak rate of $30$ blue stragglers per Gyr$^{-1}$ with an e-folding
time scale of $0.93$ Gyr. We speculate that the burst resulted from the core
collapse of the cluster at an age of about 9.8 Gyr, whereas the constantly
formed population is the result of mass transfer and mergers through binary
evolution. In that case about half the binaries in the cluster effectively
result in a blue straggler.
