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Ultracompact X-ray binaries
(UCXBs)
Nelemans & Jonker, 2006
Bildsten & Deloye, 2004
Belczynski & Taam, 2003
http://online.kitp.ucsb.edu/online/ultra_c03/
etc.
Introduction
Ultracompact binaries
(UCBs) Porb<1hr,
cannot reside a H-rich star
AM CVn systems
( 16 + 2 )
See Nelemans, 2005 for review
astro-ph/ 0409676
UCXBs
( 12 + 4 )
UCXBs
Why study UCBs?
1. strong GR sources
2. Unique astro labs (compact object, short
period variability and peculiar chemical
composition).
3. Test of binary evolution theory, in
particular the CE phase.
UCXBs
• Persistent, hard and bright X-ray sources
– Lx ~ 1036 – 1039 erg s-1
– ~108 yr above 1036 erg s-1
• NS accretor and low mass degenerate
companion
• Periods < 1 hour
Artist’s conception
of NS accreting
from a WD
Pulse frequency as a function of orbital phase (XTE J1751 -305)
Markwardt et al. 2002
M S3 sin 3 i
PK X3
f X (M S , M X ) 

( M X  M S ) 2 G
Mass functions of three X-ray
MSPs in UCXBs
• 1751 -305: 1.28×10-6 M_sun, 42min, 2.3ms
• 0929 -314: 2.7×10-7 M_sun, 44min, 5.4ms
• 1807 -294: 1.6×10-7 M_sun (smallest mass
function among all stellar binaries), 40min,
5.25ms
An indirect evidence for UCXBs
Van Paradijs &
McClintock,
1994
Ne/O/C
emission lines-another
fingerprint of
UCXBs?
X-ray spectra
4U 1626 -67
an oxygen/neon
rich accretion disc
(Schulz et al.,
2001)
Optical spectral
4U 0614 +09,
Carbon-oxygen
accretion disc
Open questions:
Cold/Hot white dwarf model
(Deloye & Bildsten, 2003)
M S3 sin 3 i
PK X3
f X (M S , M X ) 

( M X  M S ) 2 G
UCXBs as bright X-ray sources in
elliptical galaxies?
(Bildsten & Deloye, 2004)
Origin?
• Dynamical or primordial?
Origin 1: exchange interaction
Red-white binary enters
from right
green enters from left
chaos ensues eventually
ejecting white
Origin 2: RG NS collision
• RG NS collisions
– If RG is massive CE phase can cause inspiral
– Otherwise RG envelope is ejected leaving an
eccentric WD-NS binary
• Subsequent gravitational radiation causes inspiral
Origin 3:
• Descendants of primordial binaries
Belczynski & Taam
Formation channels
UCXB
Calibration
Galactic SFR ~ 1-3 M /yr (Blitz 1997)
or 1~10 M /yr (Gilmore 2001).
Uncertainties:
X-ray duty cycle for transients, 33
CE evolution (α×λ=0.1), 20
IMF (independent secondary), 10
478*100/33/20/10=7
Thanks for your patience!
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