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Evolutionary Sequences For Low-And-Intermediate-Mass
X-Ray Binaries
Ph. Podsiadlowski
S. Rappaport
E. D. Pfahl
Introduction
• LMXBs: discovered 40 yr ago• Porb<10 days• No luminous companion stars• The only one case confirmed: Cyg X-2• LMXBs may descend from IMXBs
⊙MM donor 76.0~
dayshrPin 1004~
Binary Calculations
• Roche lobe radius:
• Mass transfer rate:
• Angular momentum loss:
• Angular momentum loss:
Binary Calculations
(1): Systems evolving to long periods
(2): Systems evolving to short periods
(3): More massive systems Experiencing dynamical
mass transfer and spiral-in
Very few systems should be observable in the early
rapid phase and X-ray binaries are mostly likely to have a relatively low mass
secondary when they are observerd at the present
epoch
Thermal Timescale Mass Transfer
• Mass-radius exponents:
In radiative stars, a large fraction of the envelope (in radius) contains very
little mass
The systems becomestemporarily detached when the H-burningshell stars to move
into the region with agradient in hydrogen
abundance,established duringthe hydrogen coreburning phase andthe giant shrinks
significantly
The early mass transfer phase can bedivided into two separate phases:(1):a phase of atmospheric Roche
lobe overflow where the mass transfer rate increases exponentially,(2): a phase where the high-entropy material in the low-density envelope
of the secondary is lost
The drop in Pmin at 13 hr occurs for amodel where the secondary has just exhausted hydrogen in the center at
the beginning of mass transfer
Application to The Population of X-Ray Binaries
• Issues: (1) how unique are the evolutionary paths we have found, (2) are types of systems suggested by other reso
nably long-lived phases of our binary evolutions represented in the observed binary X-ray source population
(3) is our complete ensemble of binary evoltuion models consistent with the overall population of observed LMXBs and IMXBs?
Application to Binary Millisecond Pulsars
In the Galaxy plane, binary radio pulsars classes:
(1):one major class involves systems with low-mass companions.
(2):the ones with substantially more massive white dwarf companions
(3):systems containing planetary mass companions
(4):systems consist of a pair of neutron stars
A outstanding problem: the birthrate problem
Application to Binary Millisecond Pulsars