Stellar, brown dwarf and multiple star properties from hydrodynamical simulations of star cluster formation

By Matthew R. Bate. 2008

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We report the statistical properties of stars, brown dwarfs and multiple systems obtained from the largest hydrodynamical simulation of star cluster formation to date that resolves masses down to the opacity limit for fragmentation (a few Jupiter masses). The simulation is essentially identical to that of Bate, Bonnell & Bromm except that the initial molecular cloud is larger and more massive. It produces more than 1250 stars and brown dwarfs, providing unprecedented statistical information that can be compared with observational surveys. The calculation uses sink particles to model the stars and brown dwarfs. Part of the calculation is rerun with smaller sink particle accretion radii and gravitational softening to investigate the effect of these approximations on the results. We find that hydrodynamical/sink particle simulations can reproduce many of the observed stellar properties very well. Multiplicity as a function of the primary mass, the frequency of very low mass (VLM) binaries, general trends for the separation and mass ratio distributions of binaries and the relative orbital orientations of triples systems are all in reasonable agreement with observations. We also examine the radial variations of binarity, velocity dispersion and mass function in the resulting stellar cluster and the distributions of disc truncation radii due to dynamical interactions. For VLM binaries, because their separations are typically close, we find that their frequency is sensitive to the sink particle accretion radii and gravitational softening used in the calculations. Using small accretion radii and gravitational softening results in a frequency of VLM binaries similar to that expected from observational surveys (≈20 per cent). We also find that VLM binaries evolve from wide, unequal-mass systems towards close equal-mass systems as they form. The two main deficiencies of the calculations are that they overproduce brown dwarfs relative to stars and that there are too few unequalmass binaries with K- and G-dwarf primaries. The former of these is likely due to the absence of radiative feedback and/or magnetic fields.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/e3b6bb75182aa2d959deede52b42982256607990

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Citations in the corpus

Simulations of the grand design galaxy M51: a case study for analysing tidally induced spiral structure (2009, methodology): “…Yoshida & White 2001; Springel 2005), which has previously been applied to simulations of interacting galaxies (e.g. Cox et al. 2006; Jáchym et al. 2007), our code has predominantly been used for simulations of star formation (e.g. Bate, Bonnell & Bromm 2003; Price & Bate 2008; Bate 2009a,b).”
Global hierarchical collapse in molecular clouds. Towards a comprehensive scenario (2019, methodology): “Numerical simulations using a variety of schemes and setups have successfully reproduced the high mass end of the IMF, with a slope ∼ −1, close to the −1.3 canonical value of Salpeter (e.g., Bate 2009a; Bonnell et al. 2011).”
THE VLA NASCENT DISK AND MULTIPLICITY SURVEY OF PERSEUS PROTOSTARS (VANDAM). II. MULTIPLICITY OF PROTOSTARS IN THE PERSEUS MOLECULAR CLOUD (2016, methodology): “Large simulations of entire star forming molecular clouds have been conducted with enough resolution to examine fragmentation on the scales from the cloud down to the disks (e.g., Bate 2009, 2012).”
CIRCUMVENTING THE RADIATION PRESSURE BARRIER IN THE FORMATION OF MASSIVE STARS VIA DISK ACCRETION (2010, background): “Previous theoretical models focused on different points of view, namely, the competitive accretion (Bonnell et al. 1998; Bonnell & Bate 2002; Bonnell et al. 2004; Bate 2009a, 2009b) and the turbulent core model (McKee & Tan 2003), but they agree on the formation of accretion disks.”
RADIATION-HYDRODYNAMIC SIMULATIONS OF THE FORMATION OF ORION-LIKE STAR CLUSTERS. II. THE INITIAL MASS FUNCTION FROM WINDS, TURBULENCE, AND RADIATION (2012, methodology): “…whether it be an imposed equation of state (e.g. Bate & Bonnell 2005; Jappsen et al. 2005) or the inclusion of radiative transfer, either without (Bate 2009b, 2012) or with (Krumholz et al. 2007a, 2010, 2011; Offner et al. 2009; Urban et al. 2010) the further step of including stellar radiation.”
A COMPLETE SPECTROSCOPIC SURVEY OF THE MILKY WAY SATELLITE SEGUE 1: THE DARKEST GALAXY (2010, background): “10 AU) are expected to form via disk fragmentation (e.g., Kratter et al. 2010) or interactions between protostellar cores (e.g., Bate 2009), neither of which should be very sensitive to metallicity (M. Krumholz 2010, private communication).”
WIDE COMPANIONS TO HIPPARCOS STARS WITHIN 67 pc OF THE SUN (2012, background): “Combined with information on closer pairs also available for this sample, it will lead to the unbiased multiplicity statistics much needed as a benchmark for star-formation theories (Bate 2009).”
Individual Dynamical Masses of Ultracool Dwarfs (2017, result): “In fact, our larger sample here is less consistent with the Bate (2009) results that do not predict as many nearly circular orbits.”
RESOLVING THE LUMINOSITY PROBLEM IN LOW-MASS STAR FORMATION (2011, background): “The zero time is defined as the moment of formation of the central star. cur in massive disks and is reported in other numerical studies of disk fragmentation (Stamatellos & Whitworth 2009; Bate 2009; Basu & Vorobyov 2011).”
Adaptive Optics for Astronomy (2012, background): “The favoured model to explain these population differences, for which recent hydrodynamical simulations are reported by Bate (2009), suggests that older (∼Gyr) field brown dwarfs are systems that have been ejected at speeds of a few kms−1 from the cluster in which they formed.”
THE ASTRALUX LARGE M-DWARF MULTIPLICITY SURVEY (2012, background): “Also, it could for instance be the case that the mass ratio distribution depends on semimajor axis (e.g., Delfosse et al. 2004; Bate 2009).”
The VAST Survey - III. The multiplicity of A-type stars within 75 pc (2013, background): “This trend is consistent with predictions of the frequency of binary systems determined from numerical simulations (Sterzik & Durisen 2003; Hubber & Whitworth 2005; Bate 2009, 2012), although the functional form of the increase does differ in all but the latter simulation (Fig.”
The VLA/ALMA Nascent Disk and Multiplicity (VANDAM) Survey of Orion Protostars. II. A Statistical Characterization of Class 0 and Class I Protostellar Disks (2020, methodology): “However, models using smoothed particle hydrodynamics (SPH) can achieve higher resolution while still sampling the molecular cloud scales, such as in Bate (2009, 2012).”
Imaging Extrasolar Giant Planets (2016, background): “…theories of planet formation via core accretion and disk instability and may instead represent the tail end of brown dwarf companion formation, perhaps as opacity-limited fragments of turbulent, collapsing molecular cloud cores (e.g., Low & Lynden-Bell 1976; Silk 1977; Boss 2001; Bate 2009).”
On the diversity and statistical properties of protostellar discs (2018, methodology): “Bate (2009a, 2012) present statistics on the misalignment angles of orbits in triple systems, and the misalignments between sink particle spins and orbits in binary systems, both of which display some similar trends to observed systems.”
MAPPING THE SHORES OF THE BROWN DWARF DESERT. II. MULTIPLE STAR FORMATION IN TAURUS–AURIGA (2011, methodology): “Both of these results can be seen in hydrodynamic simulations (Bate et al. 2000; Delgado-Donate et al. 2004; Bate 2009).”
Phantom: A Smoothed Particle Hydrodynamics and Magnetohydrodynamics Code for Astrophysics (2017, background): “Similarly, the sphng code (Benz et al., 1990; Bate, 1995) has been a workhorse for our group for simulations of star formation (e.g. Price & Bate, 2007, 2009; Price et al., 2012; Lewis et al., 2015) and accretion discs (e.g. Lodato & Rice, 2004; Cossins et al., 2009), contains a rich array of…”