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