Colour-magnitude diagrams ( CMDs ) are powerful tools that might be used to infer stellar properties in globular clusters ( GCs ) , for example , the binary fraction and their mass ratio ( q ) distribution .
In the past few years , observations have revealed that q distributions of GC main-sequence ( MS ) binaries are generally flat , and a distribution characterized by a strong increase towards q \approx 1 is not typical in GCs .
In numerical simulations of GC evolution with the initial binary population ( IBP ) described by Kroupa , synthetic CMD colour distributions exhibit a peak associated with binaries that have q \approx 1 .
While the Kroupa IBP reproduces binary properties in star-forming regions , clusters and the Galactic field , the peak in the q distribution towards q \approx 1 observed for GC simulations is not consistent with distributions derived from observations .
The objective of this paper is to refine and further improve the physical formulation of pre-main-sequence eigenevolution proposed by Kroupa in order to achieve CMD colour distributions of simulated GC models similar to those observed in real GCs , and to get a similarly good agreement with binary properties for late-type binaries in the Galactic field .
We present in this paper a modified Kroupa IBP , in which early-type stars follow observational distributions , and late-type stars are generated according to slightly modified pre-main-sequence eigenevolution prescriptions .
Our modifications not only lead to a qualitatively good agreement with respect to long-term observations of late-type binaries in the Galactic field , but also resolve the above-mentioned problem related to binary distributions in GC models .