The dynamical evolution of Taurus-Auriga-type aggregates

Star formation in the Taurus-Auriga (TA) molecular clouds is producing binary-rich aggregates containing at most a few dozen systems within a region spanning 1 pc without massive stars. This environment is very different from another well-studied star-forming event which produced the Orion Nebula cluster (ONC). The ONC contains a few thousand systems within a region of 1 pc including massive stars. Differences between these two environments have been found. Notably, the ONC has a significantly smaller binary proportion but a significantly larger number of isolated brown dwarfs (BDs) per star than TA. The aim of the present project is to investigate if these differences can be explained through stellar-dynamical evolution alone. The stellar-dynamical issue is very relevant because dense environments destroy binaries liberating BD companions, possibly leading to the observed difference between the TA and ONC populations. Here a series of high-precision N-body models of TA-like embedded aggregates are presented, assuming the standard reference star formation model for the input populations according to which stars and BDs form with the same kinematical, spatial and binary properties. After a discussion of the general evolution of the aggregates, it is shown that the binary population indeed remains mostly unevolved. Therefore TA-type star formation cannot have added significantly to the Galactic field population. The standard model leads to BDs tracing the stellar distribution, apart from a high-velocity tail (v greater than or similar to 1 km s(-1)) which leads to a more widely distributed spatial distribution of single BDs. The slow-moving BDs, however, retain a high binary proportion, this being an important observational diagnostic for testing against the embryo-ejection hypothesis. Inferences about the initial mass function and the binary star orbital distribution functions are presented in two accompanying papers with useful implications for star formation and the possible origin of BDs.