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Rotation of Massive Stars

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Rotation of Massive Stars & Formation of Be stars Shao Yong 2013-06-17 1. Rotation rates of massive stars: the role of binary interaction through tides, mass ... – PowerPoint PPT presentation

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Title: Rotation of Massive Stars


1
Rotation of Massive Stars Formation of Be
stars
Shao Yong 2013-06-17
2
1. Rotation rates of massive stars the role of
binary interaction through tides, mass
transfer, and mergers
( de Mink et al. 2013, ApJ, 764, 166 )
1. the effect of tides
( Zahn 1977, Hurley et al. 2002)
Synchronization and circularization time-scale
Usually
3
2. the transfer of angular momentum during mass
transfer
moment of inertia
4
Transfer of Angular Momentum Accretion
the minimum distance Rmin between the accretion
stream and the accreting star
( Ulrich Burger 1976 )
the specific angular momentum of the impact stream
accreting from the inner radius of the disk, the
specific angular momentum of a Keplerian orbit
with a radius equal to the stellar radius
It is unclear how much stars can accrete after
reaching the Keplerian limit. Here, following
Paczynski (1991) and Popham Narayan (1991) who
argue that the accretion disk regulates the mass
and angular momentum flux through viscous
coupling allowing the star to continue to
accrete.
5
3. mergers
a critical mass ratio qcrit
assuming that the stars come in contact when Macc
/ Mdon lt qcrit
if the donor star is a main-sequence star,
qcrit,MS 0.65
when the donor fills its Roche lobe when crossing
the Hertzsprung gap, qcrit,HG 0.4
assuming that a merger product efficiently loses
the excess angular momentum, such that it rotates
at near Keplerian rotation when it has settled to
its thermal equilibrium structure.
assuming that a fraction µloss 0.1 of the total
system mass is lost during the merger and that a
small fraction µmix 0.1 of the envelope is
mixed into the convective core
6
4. some results of this paper
7
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10
2. Formation of Be stars
  • preliminary cognition of Be stars

( Pols et al. 1991 )
1. Be stars are in interacting binaries and the
Be phenomenon is caused by an accretion disc of
material lost by Roche-lobe filling companion. 2.
the so-called Be mechanism, in which some unknown
physical mechanism causes a strongly
non-spherically symmetric wind. A rapidly
rotating B star can be formed by three ways 1.
Be stars are born spinning rapidly and the Be
phase may occur at any point in the main sequence
life time. 2. the Be phenomenon occurs during
the overall contraction phase that follows the
exhaustion of hydrogen in the core. 3. Be stars
are post-mass-transfer systems.
Conclusion no more than 60 of the population of
known Be stars should be formed by close binary
interaction
  • only a minority of the Be stars (less than 20
    and possibly as low as 5) is due to close
    binary evolution

( Van Bever Vanbeveren 1997 )
Products Be stars Helium stars, or white
dwarfs,or neutron stars
11
Definition of Be and B stars
1. Rotating at near 80 of their critical limit
( Porter Rivinius 2003 )
2. In the main sequence
3. MB(e) 320 Msun
4. detached systems
12
Input initial parameters
Mp 1 60 Msun Md 0.1 20 Msun A 3
10000 Rsun ( No RLOF for primordial systems
)
Physical processes tides mass
transfer mergers
13
Numbers of B and Be stars in the Galaxy
Birthrate of a certain individual binary
population
The sum for all systems
1. Number of B stars ( primary stars )
9.4637E6
2. Number of B stars ( donor stars )
2.1752E6
14
3. Number of Be stars
  • Mass transfer

1.111E6
  • Mergers

6.64E4 for q lt 0.1
µloss 0.1
8.365E5
7.701E5 for q gt 0.1
1.032E5 for q lt 0.1
µloss 0
1.251E6
1.148E6 for q gt 0.1
15
He stars WD NS BH
2.464E5
8.258E5
1.111E6
undisrupted disrupted
3937 3.464E4
3.858E4
undisrupted disrupted
827 148
975
For BeXBs with Porb lt 1000 d
NS BeXBs 3919 BH BeXBs 308
16
Conclusion
Fraction of Be stars in all B stars
13.9 16.3
Observed fraction of Be stars is
20 30
17
Thank you
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