Poster abstract

Since most stars are born in clusters gravitational interactions between cluster members during encounters may significantly affect the evolution of circumstellar discs. Recent findings suggest that tidal perturbations of typical circumstellar discs due to passing stars may inhibit rather than trigger disc fragmentation in typical protoplanetary discs with radii around 40~AU and masses below 0.1~$M_{\odot}$. Here we show that the tidal forces during star-star encounters can trigger fragmentation between 100~AU and 200~AU in extended and massive discs ($\approx0.5\,M_{\odot}$) that are observed around young stars. In our computations, otherwise non-fragmenting massive discs, once perturbed, fragment into several objects between about 0.01 and 0.1~$M_{\odot}$, i.e. over the whole brown dwarf mass range. Typically these orbit on highly eccentric orbits or are even ejected, and sometimes even form binaries. Our scenario provides a possible formation mechanism for brown dwarfs and very massive planets which, interestingly, leads to a mass distribution consistent with the canonical substellar IMF.