Embedding Lagrangian Sink Particles in Eulerian Grids
TL;DR: A new computational method for embedding Lagrangian sink particles into a Eulerian calculation, and a simple application: studying the transition from Bondi to Bondi-Hoyle accretion that occurs when a shock hits a particle undergoing Bondi accretion.
Abstract: We introduce a new computational method for embedding Lagrangian sink particles into a Eulerian calculation. Simulations of gravitational collapse or accretion generally produce regions whose density greatly exceeds the mean density in the simulation. These dense regions require extremely small time steps to maintain numerical stability. Smoothed particle hydrodynamics (SPH) codes approach this problem by introducing nongaseous, accreting sink particles, and Eulerian codes may introduce fixed sink cells. However, until now there has been no approach that allows Eulerian codes to follow accretion onto multiple, moving objects. We have removed that limitation by extending the sink particle capability to Eulerian hydrodynamics codes. We have tested this new method and found that it produces excellent agreement with analytic solutions. In analyzing our sink particle method, we present a method for evaluating the disk viscosity parameter α due to the numerical viscosity of a hydrodynamics code and use it to compute α for our Cartesian adaptive mesh refinement (AMR) code. We also present a simple application of this new method: studying the transition from Bondi to Bondi-Hoyle accretion that occurs when a shock hits a particle undergoing Bondi accretion.
Citations
More filters
TL;DR: In this article, a basic description of the collapse of a massive molecular core and a critical discussion of the three competing concepts of massive star formation are presented, including monolithic collapse in isolated cores, competitive accretion in a protocluster environment, stellar collisions and mergers in very dense systems.
Abstract: Although fundamental for astrophysics, the processes that produce massive stars are not well understood. Large distances, high extinction, and short timescales of critical evolutionary phases make observations of these processes challenging. Lacking good observational guidance, theoretical models have remained controversial. This review offers a basic description of the collapse of a massive molecular core and a critical discussion of the three competing concepts of massive star formation: ▪ monolithic collapse in isolated cores ▪ competitive accretion in a protocluster environment ▪ stellar collisions and mergers in very dense systems We also review the observed outflows, multiplicity, and clustering properties of massive stars, the upper initial mass function and the upper mass limit. We conclude that high-mass star formation is not merely a scaled-up version of low-mass star formation with higher accretion rates, but partly a mechanism of its own, primarily owing to the role of stellar mass ...
1,332 citations
TL;DR: Yt, an open source, community-developed astrophysical analysis and visualization toolkit, is presented and its methods for reading, handling, and visualizing data, including projections, multivariate volume rendering, multi-dimensional histograms, halo finding, light cone generation, and topologically connected isocontour identification are reported.
Abstract: The analysis of complex multiphysics astrophysical simulations presents a unique and rapidly growing set of challenges: reproducibility, parallelization, and vast increases in data size and complexity chief among them. In order to meet these challenges, and in order to open up new avenues for collaboration between users of multiple simulation platforms, we present yt (available at http://yt.enzotools.org/) an open source, community-developed astrophysical analysis and visualization toolkit. Analysis and visualization with yt are oriented around physically relevant quantities rather than quantities native to astrophysical simulation codes. While originally designed for handling Enzo's structure adaptive mesh refinement data, yt has been extended to work with several different simulation methods and simulation codes including Orion, RAMSES, and FLASH. We report on its methods for reading, handling, and visualizing data, including projections, multivariate volume rendering, multi-dimensional histograms, halo finding, light cone generation, and topologically connected isocontour identification. Furthermore, we discuss the underlying algorithms yt uses for processing and visualizing data, and its mechanisms for parallelization of analysis tasks.
1,238 citations
Cites background from "Embedding Lagrangian Sink Particles..."
...…underlying representation of state variables have enabled it to be extended to work with a number of other simulation codes natively, including Orion (Truelove et al. 1998; Klein et al. 1999; Krumholz et al. 2004, 2007), FLASH (Fryxell et al. 2000), Chombo (LLNL 2010) and RAMSES (Teyssier 2002)....
[...]
TL;DR: In this paper is an open source, community-developed astrophysical analysis and visualization toolkit, which is oriented around physically relevant quantities rather than quantities native to astrophysical simulation codes, including Enzo's structure adaptive mesh refinement (AMR).
Abstract: The analysis of complex multiphysics astrophysical simulations presents a unique and rapidly growing set of challenges: reproducibility, parallelization, and vast increases in data size and complexity chief among them. In order to meet these challenges, and in order to open up new avenues for collaboration between users of multiple simulation platforms, we present yt (available at this http URL), an open source, community-developed astrophysical analysis and visualization toolkit. Analysis and visualization with yt are oriented around physically relevant quantities rather than quantities native to astrophysical simulation codes. While originally designed for handling Enzo's structure adaptive mesh refinement (AMR) data, yt has been extended to work with several different simulation methods and simulation codes including Orion, RAMSES, and FLASH. We report on its methods for reading, handling, and visualizing data, including projections, multivariate volume rendering, multi-dimensional histograms, halo finding, light cone generation and topologically-connected isocontour identification. Furthermore, we discuss the underlying algorithms yt uses for processing and visualizing data, and its mechanisms for parallelization of analysis tasks.
1,127 citations
TL;DR: In this paper, the authors derived an analytic prediction for the star formation rate in environments ranging from normal galactic disks to starbursts and ULIRGs in terms of the observables of those systems.
Abstract: We derive an analytic prediction for the star formation rate in environments ranging from normal galactic disks to starbursts and ULIRGs in terms of the observables of those systems. Our calculation is based on three premises: (1) star formation occurs in virialized molecular clouds that are supersonically turbulent; (2) the density distribution within these clouds is lognormal, as expected for supersonic isothermal turbulence; and (3) stars form in any subregion of a cloud that is so overdense that its gravitational potential energy exceeds the energy in turbulent motions. We show that a theory based on this model is consistent with simulations and with the observed star formation rate in the Milky Way. We use our theory to derive the Kennicutt-Schmidt law from first principles and make other predictions that can be tested by future observations. We also provide an algorithm for estimating the star formation rate that is suitable for inclusion in numerical simulations.
1,043 citations
TL;DR: In this paper, the authors study two limiting cases of turbulence forcing in numerical experiments: solenoidal (divergence-free) forcing and compressive (curl-free), and compare their results to observations.
Abstract: Context. Density and velocity fluctuations on virtually all scales observed with modern telescopes show that molecular clouds (MCs) are turbulent. The forcing and structural characteristics of this turbulence are, however, still poorly understood.Aims. To shed light on this subject, we study two limiting cases of turbulence forcing in numerical experiments: solenoidal (divergence-free) forcing and compressive (curl-free) forcing, and compare our results to observations.Methods. We solve the equations of hydrodynamics on grids with up to 10243 cells for purely solenoidal and purely compressive forcing. Eleven lower-resolution models with different forcing mixtures are also analysed.Results. Using Fourier spectra and Δ -variance, we find velocity dispersion-size relations consistent with observations and independent numerical simulations, irrespective of the type of forcing. However, compressive forcing yields stronger compression at the same rms Mach number than solenoidal forcing, resulting in a three times larger standard deviation of volumetric and column density probability distributions (PDFs). We compare our results to different characterisations of several observed regions, and find evidence of different forcing functions. Column density PDFs in the Perseus MC suggest the presence of a mainly compressive forcing agent within a shell, driven by a massive star. Although the PDFs are close to log-normal, they have non-Gaussian skewness and kurtosis caused by intermittency. Centroid velocity increments measured in the Polaris Flare on intermediate scales agree with solenoidal forcing on that scale. However, Δ -variance analysis of the column density in the Polaris Flare suggests that turbulence is driven on large scales, with a significant compressive component on the forcing scale. This indicates that, although likely driven with mostly compressive modes on large scales, turbulence can behave like solenoidal turbulence on smaller scales. Principal component analysis of G216-2.5 and most of the Rosette MC agree with solenoidal forcing, but the interior of an ionised shell within the Rosette MC displays clear signatures of compressive forcing.Conclusions. The strong dependence of the density PDF on the type of forcing must be taken into account in any theory using the PDF to predict properties of star formation. We supply a quantitative description of this dependence. We find that different observed regions show evidence of different mixtures of compressive and solenoidal forcing, with more compressive forcing occurring primarily in swept-up shells. Finally, we emphasise the role of the sonic scale for protostellar core formation, because core formation close to the sonic scale would naturally explain the observed subsonic velocity dispersions of protostellar cores.
778 citations
References
More filters
01 Jan 1994
TL;DR: The Diskette v 2.06, 3.5''[1.44M] for IBM PC, PS/2 and compatibles [DOS] Reference Record created on 2004-09-07, modified on 2016-08-08.
Abstract: Note: Includes bibliographical references, 3 appendixes and 2 indexes.- Diskette v 2.06, 3.5''[1.44M] for IBM PC, PS/2 and compatibles [DOS] Reference Record created on 2004-09-07, modified on 2016-08-08
19,881 citations
"Embedding Lagrangian Sink Particles..." refers methods in this paper
...Instead, we integrate the particles forward through a time ∆t using a Bulirsch-Stoer method with an adaptive time step and error control (Press et al. 1992)....
[...]
6,206 citations
"Embedding Lagrangian Sink Particles..." refers methods in this paper
...The accretion formalism thus serves a function analogous to the extrapolation procedure used to find boundary pressure in SPH sink particle or Eulerian sink cell formalisms....
[...]
...Thus, it extends to Eulerian codes one of the heretofore unique advantages of SPH, while retaining the accurate treatment of shocks and radiative transfer capability which are found in Eulerian approaches....
[...]
...Lagrangian approaches, such as SPH (Gingold and Monaghan 1977; Lucy 1977) and adaptive Eulerian approaches, such as AMR (Berger and Oliger 1984; Berger and Collela 1989; Bell et al. 1994), fare significantly better in this regard by following the mass and adding resolution elements only in regions of interest....
[...]
...Smoothed particle hydrodynamics (SPH) codes approach this problem by introducing non-gaseous, accreting sink particles, and Eulerian codes may introduce fixed sink cells....
[...]
...Note that these criteria are roughly analogous to those used by SPH codes (Bate, Bonnell, and Price 1995; Bromm, Coppi, and Larson 2002) to create sink particles: the particle must be in a region of converging flow that is gravitationally bound....
[...]
Book•
01 Jan 2009
TL;DR: In this article, the authors present references and index Reference Record created on 2004-09-07, modified on 2016-08-08 and a reference record created on 2003-09 -07.
Abstract: Note: Includes references and index Reference Record created on 2004-09-07, modified on 2016-08-08
5,777 citations
TL;DR: A finite-size particle scheme for the numerical solution of two-and three-dimensional gas dynamical problems of astronomical interest is described and tested in this article, which is then applied to the fission problem for optically thick protostars.
Abstract: A finite-size particle scheme for the numerical solution of two- and three-dimensional gas dynamical problems of astronomical interest is described and tested. The scheme is then applied to the fission problem for optically thick protostars. Results are given, showing the evolution of one such protostar from an initial state as a single, rotating star to a final state as a triple system whose components contain 60% of the original mass. The decisiveness of this numerical test of the fission hypothesis and its relevance to observed binaries are briefly discussed.
5,508 citations
"Embedding Lagrangian Sink Particles..." refers methods in this paper
...Lagrangian approaches, such as SPH (Gingold and Monaghan 1977; Lucy 1977) and adaptive Eulerian approaches, such as AMR (Berger and Oliger 1984; Berger and Collela 1989; Bell et al. 1994), fare significantly better in this regard by following the mass and adding resolution elements only in regions…...
[...]
TL;DR: Protostars and Planets VI brings together more than 250 contributing authors at the forefront of their field, conveying the latest results in this research area and establishing a new foundation for advancing our understanding of stellar and planetary formation as mentioned in this paper.
4,461 citations