Simulations of protostellar collapse using multigroup radiation hydrodynamics. I. The first collapse

Radiative transfer plays a major role in the process of star formation. Many simulations of gravitational collapse of a cold gas cloud followed by the formation of a protostellar core use a grey treatment of radiative transfer coupled to the hydrodynamics. However, dust opacities which dominate extinction show large variations as a function of frequency. In this paper, we used frequency-dependent radiative transfer to investigate the influence of the opacity variations on the properties of Larson's first core. We used a multigroup M1 moment model in a 1D radiation hydrodynamics code to simulate the spherically symmetric collapse of a 1 solar mass cloud core. Monochromatic dust opacities for five different temperature ranges were used to compute Planck and Rosseland means inside each frequency group. The results are very consistent with previous studies and only small differences were observed between the grey and multigroup simulations. For a same central density, the multigroup simulations tend to produce first cores with a slightly higher radius and central temperature. We also performed simulations of the collapse of a 10 and 0.1 solar mass cloud, which showed the properties of the first core to be independent of the initial cloud mass, with again no major differences between grey and multigroup models. For Larson's first collapse, where temperatures remain below 2000 K, the vast majority of the radiation energy lies in the IR regime and the system is optically thick. In this regime, the grey approximation does a good job reproducing the correct opacities, as long as there are no large opacity variations on scales much smaller than the width of the Planck function. The multigroup method is however expected to yield more important differences in the later stages of the collapse when high energy (UV and X-ray) radiation is present and matter and radiation are strongly decoupled.Comment: 9 pages, 5 figures, accepted for publication in A&

Collimated jets from the first core

We have performed Smoothed Particle Magnetohydrodynamics (SPMHD) simulations demonstrating the production of collimated jets during collapse of 1 solar mass molecular cloud cores to form the `first hydrostatic core' in low mass star formation. Recently a number of candidate first core objects have been observed, including L1448 IRS2E, L1451-mm and Per Bolo 58, although it is not yet clear that these are first hydrostatic cores. Recent observations of Per Bolo 58 in particular appear to show collimated, bipolar outflows which are inconsistent with previous theoretical expectations. We show that low mass first cores can indeed produce tightly collimated jets (opening angles <~ 10 degrees) with speeds of ~2-7 km/s, consistent with some of the observed candidates. We have also demonstrated, for the first time, that such phenomena can be successfully captured in SPMHD simulations.Comment: 5 pages, 4 figures, accepted to MNRAS Letters. Movies at http://users.monash.edu.au/~dprice/pubs/jet

The Properties of Prestellar Discs in Isolated and Multiple Prestellar Systems

We present high-resolution 3D smoothed particle hydrodynamics simulations of the formation and evolution of protostellar discs in a turbulent molecular cloud. Using a piecewise polytropic equation of state, we perform two sets of simulations. In both cases we find that isolated systems undergo a fundamentally different evolution than members of binary or multiple systems. When formed, isolated systems must accrete mass and increase their specific angular momentum, leading to the formation of massive, extended discs, which undergo strong gravitational instabilities and are susceptible to disc fragmentation. Fragments with initial masses of 5.5 M_jup, 7.4 M_jup and 12 M_jup are produced in our simulations. In binaries and small clusters, we observe that due to competition for material from the parent core, members do not accrete significant amounts of high specific angular momentum gas relative to isolated systems. We find that discs in multiple systems are strongly self-gravitating but that they are stable against fragmentation due to disc truncation and mass profile steeping by tides, accretion of high specific angular momentum gas by other members, and angular momentum being redirected into members' orbits. In general, we expect disc fragmentation to be less likely in clusters and to be more a feature of isolated systems.Comment: 15 pages, 21 figures. Accepted for publication in MNRA

Collapse of a molecular cloud core to stellar densities: stellar core and outflow formation in radiation magnetohydrodynamics simulations (dataset)

This repository contains the datasets from the original smoothed particle hydrodynamics (SPH) calculations for the associated paper, including most dump files. It also includes all of the scripts for generating the figures that appear in the paper. These are contained either in the Figure_Generation.zip file or in the Paper.zip file. The former mainly contains SPLASH scripts (see below) for generating images from the SPH dump files. The latter mainly contains the final (or intermediate) SPLASH figures, plus the data files and scripts for making the other figures (line plots). Line plots use supermongo scripts. There are 5 main SPH calculations discussed in the paper, using 3 million SPH particles (3M) and with magnetic mass-to-flux ratios of 5, 10, 20, 100, and infinity (e.g. MF05). The outputs from each calculation are found in the zip files that begin with RMHD_MF*. For example, RMHD_MF05_3M.zip contains all the output (and executable) from the 3 million particle calculation with mass-to-flux ratio 5, except the dump files. The dump files are contained in a series of zip files such as: RMHD_MF05_3M_0200_0219.zip which contains 20 dump files, numbers 200 to 219. The dump files are included in groups to allow downloads in reasonably small (~20 GB) chunks, since the entire repository is ~3 TB. Also included is the output from the 1 million particle, mass-to-flux ratio 5 calculation (which was used for resolution testing in the Appendix of the paper). Only the single dump file from the 10 million particle calculation which was used to generate figure 22 is included in the respository (within the Figure_Generation.zip file) because the dump files from the entire calculation occupied another 1 TB of disk space. The SPH dump files for each calculation begin at TEST000 at time zero and then are numbered sequentially. The spacing in time is not regular (it generally decreases). The SPH dump files are Fortran binary files, written in big endian format and generated by the sphNG code. They can be read, visualised, and manipulated using the free, publicly available SPLASH visualisation code (which reads sphNG dump files), written by Daniel Price, that can be downloaded from: http://users.monash.edu.au/~dprice/splash/ Finally, the MovieAll.zip file contains the SPLASH scripts for generating the density movies associated with the paper that can be found at: http://www.astro.ex.ac.uk/people/mbate/Animations/stellarcore.htmlThis is the dataset that was used to produce the paper published in MNRAS. It contains the output from each of the SPH simulations, including dump files and the scripts used to generate the figures for the paper. To view the paper follow the DOI above or http://hdl.handle.net/10871/14622University of Exeter Visiting International Academic FellowshipMonash UniversityAustralian Research Council Discovery Project GrantEndeavour IPRS and APA postgraduate research scholarshipsUniversity of Exeter Supercomputer: jointly funded by Science and Technology Facilities Council (STFC), Large Facilities Capital Fund of BIS, and the University of ExeterDiRac Complexity computer: jointly funded by Science and Technology Facilities Council (STFC) and the Large Facilities Capital Fund of BI