Transcript - Lorentz Center

from an evolutionary point of view
Ines Brott (Utrecht),
Matteo Cantiello (Utrecht),
Joke Claeys (Utrecht)
Evert Glebbeek (Hamilton),
Adrian Hamers (Utrecht),
Rob Izzard (Brussels),
Norbert Langer (Bonn),
Onno Pols (Utrecht),
Sung-Chul Yoon (Bonn)
Selma de Mink
Utrecht University
Lorentz Center Workshop “Stellar Mergers”
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Massive stars
o Cosmic engines, shape the universe
 Stellar winds
 UV flux
 SN explosions
o Formation and evolution poorly understood
o Very high fraction >50% in close binaries
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Mergers from binaries
o In contrast to mergers from collisions
o Binary mergers dominate in open clusters / loose OB associations
o Interaction before merging
Binary evolution
before
Merger
Evolution merger
after
Which binaries evolve
into contact?
Observational
properties, life-time?
What is their
evolutionary status?
For clusters: how many
“blue stragglers”?
What are the main
uncertainties?
Mass loss?
Mixing?
Do they end their life,
as SNe or GRBs?
1. Initial distributions
2. Evolution into contact
4. Rotationally induced
mixing in (near)
contact systems
3. Effects of rotationally
induced mixing
Observed binary fraction
Consistent with fmin = 0.5
Courtesy H. Sana
Single stars
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Mass
Binary stars
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(Metallicity )
(Rotation Rate )
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Mass primary
Mass ratio
Orbital period
(Eccentricity)
(Metallicity)
(Rotation rates 2x)
Data for six open clusters and OB associations
~50 % of the objects is detected a spectroscopic binary
Log (Period)
Mass Ratio
Proceedings paper: Sana et al. 2009
Data for six open clusters and OB associations
~50 % of the objects is detected a spectroscopic binary
Log (Period)
Flat in log P?
-> over abundance of
systems with P<10 days
Mass Ratio
Flat in q ?
Proceedings paper:
et al. 2009
For Sana
q =0.3-1.0
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Challenges
o Selection effects
o Evolutionary effects
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Opportunities
o VLT-flames Tarantula survey
o 1000 Massive stars
o Designed to detect binaries
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Binary models tell us:
o Which binaries come into contact?
o When do they come into contact?
o What are the properties of both stars at the
moment of contact?
Step 1
 Chemical profile
 Density / entropy profile
Step 2
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Case A
o Porb <5 days
o Donor: main sequence star
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Case B
o Porb = 5 - ~ 500? days
o Donor: Hertzsprung gap: H shell burning
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Case C
o Not important for massive stars (at solar metallicity)
 Stellar wind mass loss widens orbit
 Massive stars never become giants
Log orbital period (d)
Wellstein, Langer, Braun 2001
Mass ratio M2/M1
Z=Z, M1=12M
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From a grid of ~20.000 binary models computed
for comparison with observed eclipsing binaries
De Mink, Pols, Hilditch 2007
Conservative
Mass transfer
Z=ZSMC, M1=25M
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From a grid of ~20.000 binary models computed
for comparison with observed eclipsing binaries
De Mink, Pols, Hilditch 2007
Non-conservative
Mass transfer
Z=ZSMC, M1=25M
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Which systems come into contact?
o How much mass is accreted/lost form the system
o Implementation: when? Associated angular momentum loss?
o Entropy accreted material!
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How long can the contact configuration last?
o Low mass contact systems, W Uma
o What evolutionary processes play a role? Mixing?
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Does contact imply a merger?
o Slow contact : yes
Case A
Mergers are Main Sequence stars
Slow contact
Short periods
M2 ~ M1
Equal masses -> massive mergers
Equal entropy profiles -> mixing
Rapid contact
M2/M1 < qcrit
Compared to “slow contact”
• More frequent
• Less massive
Case B
Mergers become helium burning stars
Rapid contact
(Early Case B)
M2/M1 < qcrit
Compared to Case A mergers
• More frequent
• Shorter life times
Population synthesis of Case A
mergers  Adrian Hamers
 Rotational “instabilities” mix rotating massive stars
 Eddington-Sweet circulation most efficient process
 Mixing process on tKH
Meridional
circulation
Convective
Core
Helium
at the surface
(mass fraction)
Initial
Yoon et al 2006
Slow
rotator:
Time
Standard Evolution
Fast rotator:
Chemically Homogeneous
Bifurcation :
e.g. Maeder 87, Yoon & Langer 05
RSG
WR
R~1 Rsun
Fast rotator
Slow rotator
R~1000 Rsun
Yoon, Langer & Norman, 2006
Standard Evolution
Time
Chemically Homogeneous
Single star
evolution track
1.7 days
Roche lobe overflow
Z = 10-5
M1~M2~100M
1.7 days
Z = 10-5
M1~M2~100M
H-shell burning
1.7 days
1.4 days
1.2 days
core
H-burning
Z = 10-5
M1~M2~100M
Start He-burning
1.7 days
1.4 days
1.2 days
1.15 days
Core
H-burning
Z = 10-5
M1~M2~100M
Binary evolution
before
Merger
Evolution merger
after