mass loss and evolution of low-mass x-ray binaries xiang-dong li department of astronomy nanjing...
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Mass Loss and Evolution of Low-Mass X-ray Binaries
Xiang-Dong LiDepartment of Astronomy
Nanjing University
2009-5-20
Stability of Mass Transfer
• Two mass-radius exponents
• Stability requires that after mass loss the star is still contained by its Roche lobe.
2
22 dln
dln
M
R=ξ
2dln
dln
M
RLL =ξ
),( eqad2L ξξξξ ∈<
From Soberman et al. (1997)
Stable Mass Transfer
• Driving mechanisms– Loss of orbital
angular momentum• Gravitational
radiation
• Magnetic braking
– Nuclear evolution of the companion star
From Deloye (2008)
Thermal Timescale Mass Transfer
• Mass transfer is dynamically stable but occurs on a thermal timescale if
• This requires that the donor star has a radiative envelope, or the convective envelope is not too deep.
eqLad ξξξ >>
From Deloye (2008)
Dynamically Unstable Mass Transfer
• Massive donors with a convective envelope
Common envelope evolution
Ultracompact LMXBs
Lad 0 ζζ <≤
From Deloye (2008)
Radio Pulsar Mass Measurements
PSR J1911-5958: 1.4 (+0.16,-0.10)
2S0921-630: 1.44 (±0.10)
PSR J1909-3744: 1.438 (±0.024)
PSR J0437-4715: 1.58 (±0.18)
PSR J1012+5307: 1.6 (±0.20)
M = 1.35±0.04 M ⊙
Thorsett & Chakrabarty 1999
Mass transfer is highly non-conservative
during I/LMXB evolution
Bifurcation Periods
• Model 1: conservative mass transfer + traditional MB law
• Model 2: conservative mass transfer + saturated MB law
• Model 3: non-conservative mass transfer + mass loss from L1 point + saturated MB law
• Model 4: non-conservative mass transfer + mass loss from the NS + saturated MB law