Outflow forces in intermediate-mass star formation

Abstract

Context. Protostars of intermediate-mass provide a bridge between theories of low-and high-mass star formation. Molecular outflows emerging from such sources can be used to determine the influence of fragmentation and multiplicity on protostellar evolution through the apparent correlation of outflow forces of intermediate-mass protostars with the total luminosity instead of the individual luminosity. Aims. The aim of this paper is to derive outflow forces from outflows of six intermediate-mass protostellar regions and validate the apparent correlation between total luminosity and outflow force seen in earlier work, as well as remove uncertainties caused by different methodologies. Methods. By comparing CO 6-5 observations obtained with APEX with non-LTE radiative transfer model predictions, the optical depths, temperatures and densities of the gas of the molecular outflows are derived. Outflow forces, dynamical timescales, and kinetic luminosities are subsequently calculated. Results. Outflow parameters, including the forces, were derived for all sources. Temperatures in excess of 50 K were found for all flows, in line with recent low-mass results. However, comparison with other studies could not corroborate conclusions from earlier work on intermediate-mass protostars which hypothesized that fragmentation enhances outflow forces in clustered intermediate-mass star formation. Any enhancement in comparison with the classical relation between outflow force and luminosity can be attributed to the use of a higher excitation line and improvement in methods. They are in line with results from low-mass protostars using similar techniques. Conclusions. The role of fragmentation on outflows is an important ingredient to understand clustered star formation and the link between low-and high-mass star formation. However, detailed information on spatial scales of a few 100 AU, covering all individual members is needed to make the necessary progress.