A discontinuity in the low-mass IMF - the case of high multiplicity

The empirical binary properties of brown dwarfs (BDs) differ from those of normal stars suggesting BDs form a separate population. Recent work by Thies & Kroupa revealed a discontinuity of the initial mass function (IMF) in the very low mass star regime under the assumption of a low multiplicity of BDs of about 15 per cent. However, previous observations had suggested that the multiplicity of BDs may be significantly higher, up to 45 per cent. This contribution investigates the implication of a high BD multiplicity on the appearance of the IMF for the Orion Nebula Cluster, Taurus-Auriga, IC 348 and the Pleiades. We show that the discontinuity remains pronounced even if the observed mass function (MF) appears to be continuous, even for a BD binary fraction as high as 60 per cent. We find no evidence for a variation of the BD IMF with star-forming conditions. The BD IMF has a power-law index alpha(BD) approximate to +0.3 and about two BDs form per 10 low-mass stars assuming equal-mass pairing of BDs.