Mass Loss and Evolution of Low-Mass X-ray Binaries

Xiang-Dong LiDepartment of Astronomy

Nanjing University

2009-5-20

Low-Mass X-ray Binaries (LMXBs)

LMXBs and BMSPs

Spin Periods

Radio PSRs

MS PSRs

Spin-up line

Mag

netic fi

eld

s

LMXBs

From Deloye (2008)

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)

Bifurcation Period in L/IMXB Evolution

1.5 M⊙ + 1.0 M⊙

From Pylyser & Savonije (1988)

Porb-Mwd Relation in Wide Binary Pulsars

From Rappaport et al. (1995)

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)

Evolution of IMXBs

From Podsiadlowski et al. (2001)

From Li (2002)

Dynamically Unstable Mass Transfer

• Massive donors with a convective envelope

Common envelope evolution

Ultracompact LMXBs

Lad 0 ζζ <≤

From Deloye (2008)

UC-LMXBs

TTMT

CV-like

RGB/AGB

Angular Momentum Loss by Magnetic Braking

From Andronov et al. (2001)

Standard MB

Saturated MB

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

Mass and Angular Momentum Loss

Circumbinary disk

Outflow Wind

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

From Ma & Li (2009a)

From Ma & Li (2009a)

Magnetic Capture Model for the Formation of UCXBs

From van der Sluys et al. (2005)

A CB Disk in Work

From Ma & Li (2009b)

2CB MM && δ−=

From Ma & Li (2009b)

Conclusions

• The standard model for L/IMXBs still fails to reproduce some of the main features of the observed LMXBs and MS PSRs.

• An unknown mechanism that mimics the features of a CB disk may be an important ingredient for understanding the overall evolution of I/LMXBs and CVs.