A multiwavelength view of the protostellar binary IRAS 04325+2402: a case for turbulent fragmentation

IRAS 04325+2402 (hereinafter IRAS 04325) is a complex protostellar system hosting two young stellar objects (AB and C) at a separation of 1250 au. Here, we present a new deep Gemini imaging and spectroscopy for the system covering the wavelength regime from 1 to 12 mu m as well as Submillimeter Array interferometry at 870 mu m, in combination with Spitzer and literature data. Based on this rich data set, we provide a comprehensive picture of IRAS 04325 over scales from a few au to several parsec. Object AB is a low-mass star with a disc/envelope system and an outflow cavity, which is prominently seen in infrared images. Object C, previously suspected to be a brown dwarf, is likely a very low mass star, with an effective temperature of similar to 3400 K. It features an edge-on disc and an elongated envelope, and shows strong indications for accretion and ejection activities. Both objects are likely to drive parsec-scale molecular outflows. The two objects are embedded in an isolated, dense molecular cloud core. High extinction, lack of X-ray emission, and relatively high bolometric luminosity argue for a very young age below 1 Myr. The disc/outflow systems of objects AB and C are misaligned by similar to 60 degrees against each other and by 80 degrees and 40 degrees against the orbital plane of the binary. The system might be a good case for primordial misalignment, as opposed to misalignment caused by dynamical interactions, because the outflow direction is constant and the realignment time-scale is likely larger than the system age. This favours turbulent fragmentation, rather than rotational fragmentation, as the formation scenario. We show that the spectral energy distributions and images for the two objects can be reproduced with radiative transfer models for disc/envelope systems. Our analysis provides reassurance in the established paradigm for the structure and early evolution of young stellar objects, but stresses the importance of developing three-dimensional models with sophisticated dust chemistry.