With the aim of investigating the binary population of the 700 Myr old Praesepe cluster , we have observed 149 G and K-type cluster members using adaptive optics .
We detected 26 binary systems with an angular separation ranging from less than 0.08 to 3.3 arcsec ( 15–600 AU ) .
After correcting for detection biases , we derive a binary frequency ( BF ) in the \log \mbox { P } ( days ) range from 4.4 to 6.9 of 25.3 \pm 5.4 % , which is similar to that of field G-type dwarfs ( 23.8 % , Duquennoy & Mayor 1991 ) .
This result , complemented by similar ones obtained for the 2 Myr old star forming cluster IC 348 ( Paper II ) and the 120 Myr old Pleiades open cluster ( Paper I ) , indicates that the fraction of long-period binaries does not significantly evolve over the lifetime of galactic open clusters . We compare the distribution of cluster binaries to the binary populations of star forming regions , most notably Orion and Taurus , to critically review current ideas regarding the binary formation process .
We conclude that it is still unclear whether the lower binary fraction observed in young clusters compared to T associations is purely the result of the early dynamical disruption of primordial binaries in dense clusters or whether it reflects intrinsically different modes of star formation in clusters and associations .
We also note that if Taurus binaries result from the dynamical decay of small-N protostellar aggregates , one would predict the existence of a yet to be found dispersed population of mostly single substellar objects in the Taurus cloud .