Binary stars and the fundamental initial mass function

We have carried out Monte Carlo simulations in which we generate a random p airing of objects drawn from a pre-assumed single-star power-law initial ma ss function (IMF), which we call the fundamental IMF. We show how the mass functions of primary stars and secondary stars and the mass function of the total mass of systems (if we could resolve them) differ from the underlyin g fundamental IMF for different slopes of this IMF. We also compare our res ults with the observed IMF, the binary frequency and the binary mass-ratio distributions for field stars and conclude that the fundamental IMF of subs olar mass stars could be steeper than is currently believed. In other words , the low-mass turn-over of the observed ('apparent') IMF could be spurious , if the main-sequence binary fraction of field stars is close to 100 per c ent (perhaps owing to invisible companions).