Post on 14-Jan-2016
description
Mergers in Massive Binaries
from an evolutionary point of view
Selma de MinkUtrecht University
Lorentz Center Workshop “Stellar Mergers”
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)
Massive starso Cosmic engines, shape the universe
Stellar winds UV flux SN explosions
o Formation and evolution poorly understoodo Very high fraction >50% in close binaries
Mergers from binarieso In contrast to mergers from collisionso Binary mergers dominate in open clusters / loose OB associationso Interaction before merging
Motivation
Evolutionary point of view
Binary evolutionbefore
Evolution merger after
Merger
Which binaries evolve into contact?
What is their evolutionary status?
What are the main uncertainties?
Observational properties, life-time?
For clusters: how many “blue stragglers”?
Do they end their life, as SNe or GRBs?
Mass loss?
Mixing?
Outline
1. Initial distributions
2. Evolution into contact
4. Rotationally induced mixing in (near) contact systems
3. Effects of rotationally induced mixing
Initial properties of massive binaries
Binary fraction among massive stars
Obse
rved
bin
ary
fra
ctio
n
Courtesy H. Sana
Consistent with fmin = 0.5
Key parameters
Single stars Binary stars
Mass
(Metallicity ) (Rotation Rate )
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
Cumulative distribution functions
Proceedings paper: Sana et al. 2009
Log (Period) Mass Ratio
Data for six open clusters and OB associations~50 % of the objects is detected a spectroscopic binary
Cumulative distribution functions
Proceedings paper: Sana et al. 2009
Log (Period) Mass Ratio
Flat in log P?
-> over abundance of systems with P<10 days
Flat in q ?
For q =0.3-1.0
Summary: initial binary properties Challenges
o Selection effectso Evolutionary effects
Opportunitieso VLT-flames Tarantula surveyo 1000 Massive stars o Designed to detect binaries
Evolution into contact
Binary evolution
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?
Chemical profile
Density / entropy profile
Step 1
Step 2
Step 1: Evolution into Roche-lobe overflow
Case Ao Porb <5 dayso Donor: main sequence star
Case Bo Porb = 5 - ~ 500? dayso Donor: Hertzsprung gap: H shell burning
Case Co Not important for massive stars (at solar metallicity)
Stellar wind mass loss widens orbit Massive stars never become giants
Step 1
Step 2: Evolution into contact
Z=Z, M1=12M
Wellstein, Langer, Braun 2001
Mass ratio M2/M1
Log
orb
ital peri
od
(d)
Z=ZSMC, M1=25M
De Mink, Pols, Hilditch 2007 From a grid of ~20.000 binary models computedfor comparison with observed eclipsing binaries
Step 2: Case A contact
ConservativeMass transfer
Z=ZSMC, M1=25M
De Mink, Pols, Hilditch 2007 From a grid of ~20.000 binary models computedfor comparison with observed eclipsing binaries
Step 2: Case A contact
Non-conservativeMass transfer
Which systems come into contact?o How much mass is accreted/lost form the systemo Implementation: when? Associated angular momentum loss?
o Entropy accreted material!
How long can the contact configuration last?o Low mass contact systems, W Umao What evolutionary processes play a role? Mixing?
Does contact imply a merger?o Slow contact : yes
Uncertainties
Summary evolution into contactCase A Mergers are Main Sequence stars
Slow contact Short periodsM2 ~ M1
Equal masses -> massive mergersEqual 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
Mergers and rotational mixing
Fast rotating stars
Convective Core
Meridional circulation
Rotational “instabilities” mix rotating massive stars
Eddington-Sweet circulation most efficient process
Mixing process on tKH
Rotational mixing
Helium at the surface(mass fraction)
Initial
Yoon et al 2006
Slow rotator - fast rotator
Fast rotator:
Time
Chemically Homogeneous
Standard Evolution
e.g. Maeder 87, Yoon & Langer 05
Slow rotator:
Bifurcation :
Bifurcation
R~1000 Rsun
RSG
R~1 Rsun
WR
Fast rotator
Slow rotator
Yoon, Langer & Norman, 2006
Effects of rotational mixing in (near) contact
systems
Binary contextChemically HomogeneousStandard Evolution
Time
Z = 10-5
M1~100M
Single star evolution track
Binary models1.7 days
Roche lobe overflow
Z = 10-5
M1~M2~100M
Zoom in1.7 days
Z = 10-5
M1~M2~100M
Binary models1.7 days
1.4 days
1.2 days
core H-burning
Z = 10-5
M1~M2~100M
H-shell burning
Binary models1.7 days
1.4 days
1.2 days
1.15 days
Start He-burning
Z = 10-5
M1~M2~100M
Core H-burning
Summary
Summary
Binary evolutionbefore
Evolution merger after
Merger