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Population synthesis with dynamics

Population synthesis with dynamics. or the problems that we face. Natasha Ivanova MODEST-6 August 2005. What is population synthesis?.

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Population synthesis with dynamics

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  1. Population synthesis with dynamics or the problems that we face • Natasha Ivanova • MODEST-6 • August 2005

  2. What is population synthesis? Evolutionary Population Synthesis is the method of direct modeling of large populations of non-interacting objects (single or binaries in our case) with non-trivial (non-describable by simple analytic) evolution. The evolution for an object is followed from its birth till the desired moment. The goals: • to see how the population looks like from statistical point of view • to check if theory works OK and produces the same number of rare objects as observed • predict new objects!

  3. Basics of the binary dynamics • Collision time coll: time between two successive collisions, coll= 1/ncS • Hardness : ratio between binary binding energy and kinetic energy of an average object • Soft binaries <1: get softer (Heggie 1975); very likely to be destroyed through ionization • Hard binaries >1: get harder; the encounter can result in the exchange of the companion (smaller mass component is replaced by more massive intruder); very hard binary is likely to merge (Fregeau et al. 2004)

  4. Why do we care about binaries? Interacted and destroyed binaries

  5. Interacted and survived binaries

  6. Non-Interacted binaries Among stars with the initial masses > 0.6 Msun only 8% are both hard and did not have interactions…

  7. What do we NEED to take into account for binaries and why life is uncertain • Magnetic braking • Mass transfer events • Mergers • Common envelope events • Tidal circularization and synchronization • Accretion on WDs, Ia SN and subCh Ia • SN kicks and NS-retention: e-c SN? • Triples?!

  8. A few spices before you start to boil the soup • IMF • Mass ratio distribution? • How to pick the secondary? • Does q depend on the primary masses? • Does q depend on binary periods? • What is about “twins”? • Periods distribution? • Eccentricities distribution? • Initial binaries/triples/quadruples/quintuples and sextuples fractions?

  9. Some currently existing Population Synthesis codes for interacting binaries • Moscow (Yungleson, Tutukov, Lipunov, Postnov,…) • Seba (Portegiez Zwart, Tout, Verbunt,…) • SSE & BSE (Hurley, Pols, Tout) • Kalogera, Belczynski • Willems, Kolb • … • Brussel code (Vanbeveren & Co): interpolation between tracks for massive stars • Podsiadlowski, Rappaport, Pfahl & Han : detailed binary tracks for specific classes of systems (Ia SN, LMXBs, sdB …)

  10. Any wishes? • fast and robust • correct and powerful (not restricted to a certain class of objects) Time-scale: < one month on a modest 32-CPUs cluster (at 50% Memory-resources: 4Gb of memory (NO swapping!) 250,000 Msun GC: ~ 1,000,000 stars: • < 40 seconds per star • one star should not take more than 40kb in memory. An unavoidable fact: the evolution of a single star takes much less than the evolution of a binary, if one speaks about an interacting binary. So the code is better be able to evolve a single star on a time-scale of few seconds.

  11. GC: evolution is perturbed! • SS encounters • Mergers in physical collisions • Binary formations via physical collisions • Binary formations via tidal captures • Three and four body encounters • MT is interrupted • Eccentricity is changed • Exchange occurred and companions are now misaligned and not any more on the corotation • (multiple) physical collisions, including “dynamical” CE • triples formation

  12. How to deal with all the mess? • Learn binary evolution in the field • Build a “scenario processor” for all events • Analyze what happens - does it make any sense? • Treat specific circumstances with great details • Re-run • Run to observers • Get from observers their results and sit for a while thinking why there is no common language

  13. Formation of CV binaries: CE or encounter? Field, non-eccentric binaries

  14. CVs formation: main formation channels CE BS/BB MS-MS Destr Exch Merger Collis binary single SS BS/BB Exch CE 40% Coll RG 10% 15% CV 35%

  15. CVs: population of WDs Field “Typical” cluster

  16. Simulaions vs observations Simulations Observations

  17. PS and dynamics: some currently active codes • Hurley - open clusters, M67. • SeBa - IMBH formation, open clusters ecology • Brussel - young clusters with massive stars • Freitag - IMBH formation, Galactic center • Fregeau, Gurkan, Rasio - IMBH formation, mass segregation in globular clusters with full IMF • Ivanova, Belczynski, Fregeau, Rasio - binary fractions, compact binaries formation and evolution in globular clusters • Postnov - NS retention, MSPs

  18. Future of PS codes with dynamics Bill Paxton’s “EZ” code (Eggleton-refasted): one minute per single star Saul Rappaport and his students at MIT: large population study of binary evolution and RLO. 30,000 binaries in 24 hours at 35 nodes (~2 minutes/RLO binary!!!) http://theory.kitp.ucsb.edu/~paxton

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