probing the evolution of stellar systems
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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 - PowerPoint PPT PresentationTRANSCRIPT
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Probing the evolution of stellar systems
Andreas Zezas
Harvard-Smithsonian Center for Astrophysics
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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
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The complicated lives of stars
… but, after some time they run out of fuel White dwarf (≤8 M) Supernova (≥8 M)
Neutron star (M~1.4-3.0 M)
Black-hole (M >3.0 M)
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Basic tool : Photometry
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Basic tool : Photometry
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Main Sequence
Red Giant Branch
Horizontal Branch
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CMDs : Simple cases
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The tools : Stellar Tracks
(<m>| age, Mass, Z, stellar evolution)
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The tools : IsochronesThe tools : Isochrones
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The tools : Isochrones
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The tools : Isochrones
QuickTime™ and aYUV420 codec decompressor
are needed to see this picture.
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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
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Analogy with X-rays
• Isochrones RMF• Detection probability ARF
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The “standard method”
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The “standard method”
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The “standard method”
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The “standard method”
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Complications
• Incompleteness• Multiple populations• Uncertainties on isochrones
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CMDs: complications
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CMDs: complications
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CMDs: complications
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CMDs: more complicationsDetection
probability
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• Gaussian statistics (as
usually…)• 2 fits• All stars have equal weight• Complex mixture problem with
several free correlated
parameters• Several different sets of
isochrones
Problems with standard method
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The link with cal. uncertainties
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• 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
A new method
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The test case : The SMC
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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