Low-mass binaries in the young cluster IC 348: implications for binary formation and evolution

We report on a near-infrared adaptive optics survey of a sample of 66 low-mass members of the pre-main sequence stellar cluster IC 348. We find 12 binary systems in the separation range 0.1-8.0 arcsec. An estimate of the number of faint undetected companions is derived, before we evaluate the binary frequency in this cluster. In the orbital period range log P=5.0-7.9 days, the binary fraction in IC 348 is 19+/-5 %.This is similar to the values correspondings to G- and M-dwarfs populations in the solar neigbourhood. Substellar companions are found to be rare, or even missing, as companions of low-mass stars in the separation range we surveyed. Also, the mass ratio distribution is not peaked at q=1. We do not find any evidence for an evolution of the binary frequency with age within the age spread of the cluster of about 10 Myr. We conclude that there is no temporal evolution of the binary fraction between a few Myrs after the formation process, the zero-age main sequence and the field population. We find instead a trend for the binary fraction to be inversely correlated with stellar density, with only loose associations exhibiting an excess of binaries. Either all star-forming regions initially host a large number of binaries, which is subsequently reduced only in dense clusters on a timescale of less than 1 Myr due to numerous gravitational encounters, or specific initial conditions in the parental molecular clouds impact on the fragmentation process leading to intrinsically different binary fractions.