Evolution of Massive Stars

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EvolutionofMassive Stars
Alessandro Bressan
INAF Osservatorio Astronomico di
Padova SISSATrieste
MAGPOP Summer School - Budapest, Hungary, 2006.
August 23-25
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Beginning from the end
WHICH IS THE PATH TO THE END ?
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Why Study Massive Stars

• Provide most of the chemical mechanical energy
  input into the interstellar medium
• (stellar winds, supernova)
• Provide most of UV ionizing radiation of
  galaxies, plus power the far-IR luminosities
  through the heating of dust
• Trace the star formation process in galaxies
• Are the source of the most energetic phenomenon
  yet found (GRBs)

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Massive Stars are Extremely Rare

• For every 20 M? star in the Milky Way, there are
  roughly 105 solar-type stars.
• For every 100 M? star, there are over 106
  solar-type stars.

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The HR Diagram
MW Humphreys Davidson 79
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The HR Diagram
MW Humphreys Davidson 79
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The HR Diagram
RED SUPERGIANTS
MW Humphreys Davidson 79
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The HR Diagram
YELLOW GAP
MW Humphreys Davidson 79
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The HR Diagram
MW Humphreys Davidson 79
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Peculiar Objects
Luminous Blue Variables
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h Car
100 x more luminous in the MIR
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Wolf Rayet Stars
Luminous Blue Variables
WNL N,He,H
WC C, O
WNE N,He
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H ( He) Burning
Massive stars characterized by a simple internal
structure

• Large convective nucleus (gt 50 of the star )
• surrounded by a radiative envelope

• Opacity dominated by e-scattering

• Perfect non-degenerate EOS with dominating
  radiation pressure

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Lower Mass Range
10 - 30 MŸ
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Higher Mass Range M gt 30 MŸ
The evolution is dominated by mass-loss Note no
consistent models yet
Wind Velocity gt VESC (1000 km/s)
Mass Loss Rate 10-6 10-4 MŸ/yr
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P-Cygni profile
Absorbing column tw. the photosphere
Emitting extended envelope
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Radiative Wind Terminal Velocity
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Evolution with mass loss
Initial Mass
NO RSG but WR
A fundamental question for the evolution of
massive stars Mass-Loss vs Metallicity ?
Final Mass
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Mass-Loss Metallicity
O Supergiants
Log L/L? 7.03 (solid circles) 6.91 (open
circles) 6.76 (plus signs) 6.57 (asterisks)
6.42 (triangles) 6.30 (squares)
Kudritzki 2002
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Mass-Loss Metallicity
Wolf Rayet Stars
Large Ge dependence
h 1 to 5 ! !
90-00 small dependence
Grafener Hamann 05
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Mass LossduringRSG
Salasnich, Bressan Chiosi 99
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HR DiagramMetallicity
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HR DiagramMetallicity
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Models with Rotation
Meynet Maeder 02
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EnhancedRSGMassLoss
Salasnich, Bressan Chiosi 99
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ARE WR WELL PREDICTED ?
Massey 03

• Number Ratio WC/WN

log (O/H)12
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ARE WRsWELL PREDICTED ?
Atmospheres ?
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Mass at the end of the quiescent life
Bressan et al 93
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Effects of Rotation Maeder Meynet (02,03 etc..)
Final Mass
Initial Mass
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Remnant Mass
NS
RM
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Ultra Luminous X-Ray sourcesin Starbursts
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Conclusions

• Massive star evolution compares generally well
  with observations, yet some aspects remain unclear

Details or substantial modifications ? e.g. WR
L Teff

• RSG Mass-Loss
• changes evolution down to 15 M?
• Low Z mass loss at the Edd limit
• important for very massive stars