Simulating star formation in molecular cloud cores IV. The role of turbulence and thermodynamics

Abstract

We perform SPH simulations of the collapse and fragmentation of low-mass cores having different initial levels of turbulence (alpha_turb=0.05,0.10,0.25). We use a new treatment of the energy equation which captures the transport of cooling radiation against opacity due to both dust and gas (including the effects of dust sublimation, molecules, and H^- ions). We also perform comparison simulations using a standard barotropic equation of state. We find that -- when compared with the barotropic equation of state -- our more realistic treatment of the energy equation results in more protostellar objects being formed, and a higher proportion of brown dwarfs; the multiplicity frequency is essentially unchanged, but the multiple systems tend to have shorter periods (by a factor ~3), higher eccentricities, and higher mass ratios. The reason for this is that small fragments are able to cool more effectively with the new treatment, as compared with the barotropic equation of state. We find that the process of fragmentation is often bimodal. The first protostar to form is usually, at the end, the most massive, i.e. the primary. However, frequently a disc-like structure subsequently forms round this primary, and then, once it has accumulated sufficient mass, quickly fragments to produce several secondaries. We believe that this delayed fragmentation of a disc-like structure is likely to be an important source of very low-mass hydrogen-burning stars and brown dwarfs.

14 pages, 8 figures. Accepted for publication by A&A

References in corpus (14)

• SPLASH: An interactive visualisation tool for Smoothed Particle Hydrodynamics simulations
• Radiation-Hydrodynamic Simulations of Collapse and Fragmentation in Massive Protostellar Cores
• The impact of magnetic fields on single and binary star formation
• A SCUBA survey of Orion, the low-mass end of the core mass function
• Fragmentation of Massive Protostellar Disks
• Brown dwarf formation by gravitational fragmentation of massive, extended protostellar discs
• The effect of magnetic fields on star cluster formation
• The minimum mass for star formation, and the origin of binary brown dwarfs
• Radiative transfer and the energy equation in SPH simulations of star formation
• Can giant planets form by gravitational fragmentation of discs?
• Numerical requirements for simulations of self gravitating and non-self gravitating disks
• The relationship between the prestellar core mass function and the stellar initial mass function
• Protostellar collapse: A comparison between SPH and AMR calculations
• Star formation in molecular cores III. The effect of the turbulent power spectrum

Cited by in corpus (7)

• The Effects of Radiative Transfer on Low-Mass Star Formation
• The properties of discs around planets and brown dwarfs as evidence for disc fragmentation
• The effect of radiative feedback on disc fragmentation
• Disc formation and fragmentation using radiative non-ideal magnetohydrodynamics
• The dynamical evolution of low-mass hydrogen-burning stars, brown dwarfs and planetary-mass objects formed through disc fragmentation
• Evolution of binary seeds in collapsing protostellar gas clouds
• Double cyclic variations in orbital period of the eclipsing cataclysmic variable EX Dra