Rapid binary star evolution for N-body simulations and population synthesis (original) (raw)
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Physical Review D
We present a novel way of modeling common envelope evolution in binary and few-body systems. We consider the common envelope inspiral as driven by a drag force with a power-law dependence in relative distance and velocity. The orbital motion is resolved either by direct N-body integration or by solving the set of differential equations for the orbital elements as derived using perturbation theory. Our formalism can model the eccentricity during the common envelope inspiral, and it gives results consistent with smoothed particles hydrodynamical simulations. We apply our formalism to common envelope events from binary population synthesis models and find that the final eccentricity distribution resembles the observed distribution of post-common-envelope binaries. Our model can be used for time-resolved commonenvelope evolution in population synthesis calculations or as part of binary interactions in direct N-body simulations of star clusters.
Numerical Evolution of Single, Binary and Triple Stars
Proceedings of the International Astronomical Union, 2007
I discuss my stellar evolution codeEvin the context of simulations of large clusters of stars. It has long been able to handle single stars, and also binary stars up to a point. That point is far beyond what other codes are able to do, but well short of what is necessary for believable simulations. A recent version,Ev(Twin), can in principle deal with the contact phase of binary evolution, but it is not yet clear what the physical interaction is that needs to be simulated.An upgrade, which I hope will be only a few lines, should allow it to follow Kozai cycles with tidal friction, a process that strongly influences the orbital period of close pairs that reside within wide, non-coplanar triples. However, there are many substantial gaps in the physics of even single stars, let alone binaries or triples.
Rapid stellar and binary population synthesis with COMPAS
2021
COMPAS (Compact Object Mergers: Population Astrophysics and Statistics) is a public rapid binary population synthesis code. COMPAS generates populations of isolated stellar binaries under a set of parametrised assumptions in order to allow comparisons against observational data sets, such as those coming from gravitational-wave observations of merging compact remnants. It includes a number of tools for population processing in addition to the core binary evolution components. COMPAS is publicly available via the github repository https://github.com/TeamCOMPAS/COMPAS/, and is designed to allow for flexible modifications as evolutionary models improve. This paper describes the methodology and implementation of COMPAS. It is a living document which will be updated as new features are added to COMPAS; the current document describes COMPAS v02.21.00.
POSYDON: A General-Purpose Population Synthesis Code with Detailed Binary-Evolution Simulations
2022
Most massive stars are members of a binary or a higher-order stellar systems, where the presence of a binary companion can decisively alter their evolution via binary interactions. Interacting binaries are also important astrophysical laboratories for the study of compact objects. Binary population synthesis studies have been used extensively over the last two decades to interpret observations of compact-object binaries and to decipher the physical processes that lead to their formation. Here, we present POSYDON, a novel, binary population synthesis code that incorporates full stellar-structure and binary-evolution modeling, using the MESA code, throughout the whole evolution of the binaries. The use of POSYDON enables the self-consistent treatment of physical processes in stellar and binary evolution, including: realistic mass-transfer calculations and assessment of stability, internal angular-momentum transport and tides, stellar core sizes, mass-transfer rates and orbital periods...
A new, efficient stellar evolution code for calculating complete evolutionary tracks
Monthly Notices of the Royal Astronomical Society, 2009
We present a new stellar evolution code and a set of results, demonstrating its capability at calculating full evolutionary tracks for a wide range of masses and metallicities. The code is fast and efficient, and is capable of following through all evolutionary phases, without interruption or human intervention.
Theory of stellar population synthesis with an application to N-body simulations
2012
Aims. We present here a new theoretical approach to population synthesis. The aim is to predict colour magnitude diagrams (CMDs) for huge numbers of stars. With this method we generate synthetic CMDs for N-body simulations of galaxies. Sophisticated hydrodynamic N-body models of galaxies require equal quality simulations of the photometric properties of their stellar content. The only prerequisite for the method to work is very little information on the star formation and chemical enrichment histories, i.e. the age and metallicity of all star-particles as a function of time. The method takes into account the gap between the mass of real stars and that of the star-particles in N-body simulations, which best correspond to the mass of star clusters with different age and metallicity, i.e. a manifold of single stellar sopulations (SSP). Methods. The theory extends the concept of SSP to include the phase-space (position and velocity) of each star. Furthermore, it accelerates the building up of simulated CMD by using a database of theoretical SSPs that extends to all ages and metallicities of interest. Finally, it uses the concept of distribution functions to build up the CMD. The technique is independent of the mass resolution and the way the N-body simulation has been calculated. This allows us to generate CMDs for simulated stellar systems of any kind: from open clusters to globular clusters, dwarf galaxies, or spiral and elliptical galaxies. Results. The new theory is applied to an N-body simulation of a disc galaxy to test its performance and highlight its flexibility.
2012
In this thesis we study several aspects of dynamical evolution of stellar clusters. The results of more than 200 simulations of single-mass star clusters with different initial total mass, half-mass radius and galactocentric distance, are reported. Recent studies of star clusters show a linear relation between a star cluster's dissolution time and its two-body relaxation time in logarithmic scale. We found that the single-mass star clusters do not show such a linear relation. We present new modified initial parameters to obtain a linear relation for single-mass star clusters. Also the evolution of multi-mass clusters and their lifetime, in the presence of the Galaxy is investigated. We simulate about 90 multi-mass star clusters with the Nbody6 code. These clusters have different initial total mass, half-mass radius and galactocentric distance. Finally we investigate the evolution of the stellar mass function and show that the slopes of the mass functions decrease with time. In a...
2020
Stellar systems are broadly divided into collisional and non-collisional. The latter are large-N systems with long relaxation timescales and can be simulated disregarding two-body interactions, while either computationally expensive direct N-body simulations or approximate schemes are required to properly model the former. Large globular clusters and nuclear star clusters, with relaxation timescales of the order of a Hubble time, are small enough to display some collisional behaviour and big enough to be impossible to simulate with direct NNN-body codes and current hardware. We introduce a new method to simulate collisional stellar systems, and validate it by comparison with direct N-body codes on small-N simulations. The Multi-Particle collision for Dense stellar systems Code (MPCDSS) is a new code for evolving stellar systems with the Multi-Particle Collision method. Such method amounts to a stochastic collision rule that allows to conserve exactly the energy and momentum over a c...
Monthly Notices of the Royal Astronomical Society, 2011
A new method is presented to describe the evolution of the orbital-parameter distributions for an initially universal binary population in star clusters by means of the currently largest existing library of N -body models. It is demonstrated that a stellar-dynamical operator, Ω M ecl ,r h dyn (t), exists, which uniquely transforms an initial (t = 0) orbital parameter distribution function for binaries, D in , into a new distribution, D M ecl ,r h (t), depending on the initial cluster mass, M ecl , and half-mass radius, r h , after some time t of dynamical evolution. For D in the distribution functions derived by Kroupa (1995a,b) are used, which are consistent with constraints for pre-main sequence and Class I binary populations. Binaries with a lower energy and a higher reduced-mass are dissolved preferentially. The Ω-operator can be used to efficiently calculate and predict binary properties in clusters and whole galaxies without the need for further N -body computations. For the present set of N -body models it is found that the binary populations change their properties on a crossing time-scale such that Ω M ecl ,r h dyn (t) can be well parametrized as a function of the cluster density, ρ ecl . Furthermore it is shown that the binary-fraction in clusters with similar initial velocity dispersions follows the same evolutionary tracks as a function of the passed number of relaxation-times. Present-day observed binary populations in star clusters put constraints on their initial stellar densities, ρ ecl , which are found to be in the range 10 2 ρ ecl ( r h )/M ⊙ pc −3 2 × 10 5 for open clusters and a few×10 3 ρ ecl ( r h )/M ⊙ pc −3 10 8 for globular clusters, respectively.
Astronomy & Astrophysics
Context. Stellar systems are broadly divided into collisional and non-collisional categories. While the latter are large-N systems with long relaxation timescales and can be simulated disregarding two-body interactions, either computationally expensive direct N-body simulations or approximate schemes are required to properly model the former. Large globular clusters and nuclear star clusters, with relaxation timescales of the order of a Hubble time, are small enough to display some collisional behaviour and big enough to be impossible to simulate with direct N-body codes and current hardware. Aims. We aim to introduce a new method to simulate collisional stellar systems and validate it by comparison with direct N-body codes on small-N simulations. Methods. The Multi-Particle Collision for Dense Stellar Systems (mpcdss) code is a new code for evolving stellar systems with the multi-particle collision method. Such a method amounts to a stochastic collision rule that makes it possible to conserve the exact energy and momentum over a cluster of particles experiencing the collision. The code complexity scales with N log N in the number of particles. Unlike Monte Carlo codes, mpcdss can easily model asymmetric, non-homogeneous, unrelaxed, and rotating systems, while allowing us to follow the orbits of individual stars. Results. We evolved small (N = 3.2 × 10 4) star clusters with mpcdss and with the direct-summation code nbody6, finding a similar evolution of key indicators. We then simulated different initial conditions in the 10 4 − 10 6 star range. Conclusions. mpcdss bridges the gap between small collisional systems that can be simulated with direct N-body codes and large non-collisional systems. In principle, mpcdss allows us to simulate globular clusters such as Omega Centauri and M54, and even nuclear star clusters, which is beyond the limits of current direct N-body codes in terms of the number of particles.