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Probing the evolution of stellar systems

Probing the evolution of stellar systems. Andreas Zezas Harvard-Smithsonian Center for Astrophysics. The lives of stars : fighting against gravity. Defining parameter : Mass To avoid implosion stars must generate energy from fusion reactions

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Probing the evolution of stellar systems

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  1. Probing the evolution of stellar systems Andreas Zezas Harvard-Smithsonian Center for Astrophysics

  2. The lives of stars : fighting against gravity • Defining parameter : Mass • To avoid implosion stars must generate energy from fusion reactions • The stages of stars are determined by the type of fuel left: hydrogen, helium, carbon etc

  3. Neutron star (M~1.4-3.0 M) Black-hole (M >3.0 M) The complicated lives of stars … but, after some time they run out of fuel White dwarf (≤8 M) Supernova (≥8 M)

  4. Basic tool : Photometry

  5. Basic tool : Photometry

  6. Horizontal Branch Red Giant Branch Main Sequence

  7. CMDs : Simple cases

  8. The tools : Stellar Tracks (<m>| age, Mass, Z, stellar evolution)

  9. The tools : Isochrones The tools : Isochrones

  10. The tools : Isochrones

  11. The tools : Isochrones

  12. The recipe • Assume a star-formation scenario (model) • Take some isochrones (calibration) • Weight them by the IMF : N  M- • Mix them • Simulate (include observational biases) • Compare with observed CMD

  13. Analogy with X-rays • Isochrones  RMF • Detection probability  ARF

  14. The “standard method”

  15. The “standard method”

  16. The “standard method”

  17. The “standard method”

  18. Complications • Incompleteness • Multiple populations • Uncertainties on isochrones

  19. CMDs: complications

  20. CMDs: complications

  21. CMDs: complications

  22. CMDs: more complications Detection probability

  23. Problems with standard method • Gaussian statistics (as usually…) • 2 fits • All stars have equal weight • Complex mixture problem with several free correlated parameters • Several different sets of isochrones

  24. The link with cal. uncertainties

  25. A new method • Estimate the likelihood that each data point comes from a given isochrone • Find the likelihood for all points • Advantages • Easily generalized to n-dimensions • Easily estimate effect of different isochrones • Proper statistical treatment of uncertainties • Can include correlated uncertainties and data augmentation for missing data • Can treat as mixture problem

  26. The test case : The SMC

  27. The test case • Nearby galaxy (60 kpc) • Recent star-formation (a bit complex) • … but can observe very deep and set good constraints • on star-formation • also can obtain additional constrains from spectroscopy • ….useful for testing the results and setting priors

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