Lower Limit to Stellar Masses >/= 0.08 Msun
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Transcript of Lower Limit to Stellar Masses >/= 0.08 Msun
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Lower Limit to Stellar Masses >/= 0.08 Msun
Substellar objects – Brown Dwarfs
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Evolution of Low Mass Stars -- like the Sun < 2 – 3 Msun
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Post Main Sequence Evolution -- the Red Giant Stage
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The Sun as a red giant
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Second Red Giant Stage -- the Asymptotic Giant Branch (AGB)
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Post AGB, Planetary Nebulae and White Dwarfs -- final stage for the Sun
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White Dwarf stage – Nuclear reactions extinguished, weight of star supported by electron degeneracy
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Observations – Sirius A and B
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White Dwarf Properties
Sun as a WD ~ 0.5 – 0.7 Msun
Size ~ 2 R earth
Density 106 gm/cm3
Compare with
Mean density of Sun 1gm/cm3
core of Sun 100gm/cm3
density Earth 5.5 gm/cm3
Chandrasekhar Limit 1.4 Msun -- upper mass limit for electron degeneracy
Size depends on mass of WD
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Novae – white dwarfs in a close binary system
Companion either red giant or red dwarf
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Evolution of the Most Massive Stars -- >/= 10 Msun
He-burning begins as a red supergiant, no electron degenerate core
He C,O , C,O heavier elements up to Fe, as a red supergiant or successive transits across HR diagram
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Most massive stars are unstable, lose mass, some in high mass loss events
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Massive Stars – final stages (days!)
Supernova!
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Enrichment of the Interstellar Medium – abundances of the elements
Thousands of SNe seen 1936 – 2013 but in other galaxies
Rate 1 -2 /galaxy/100 yrs
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Historical Supernovae in Milky Way and supernova remnants
Crab Nebula – 1054
Tycho’s 1572
Kepler’s 1604
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Supernovae remnants
The Veil Nebula
The Crab Nebula -- 1054
Cas A – Tycho’s
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Naked-eye supernova – 1987A -- not in our galaxy --- LMC
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The Importance of the Crab Nebula