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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 reviewastro-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 3 3 3sin
( , )( ) 2
S XX S X
X S
M i PKf M M
M M 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
4U 1626 -67an oxygen/neon rich accretion disc
(Schulz et al., 2001)
Ne/O/C emission lines-- another fingerprint of UCXBs?
X-ray spectra
Optical spectral
4U 0614 +09,Carbon-oxygen accretion disc
Open questions:
Cold/Hot white dwarf model (Deloye & Bildsten, 2003)
3 3 3sin( , )
( ) 2S X
X S XX S
M i PKf M M
M M G
UCXBs as bright X-ray sources in elliptical galaxies?
(Bildsten & Deloye, 2004)
Origin?
• Dynamical or primordial?
Red-white binary enters from right
green enters from left
chaos ensues eventually ejecting white
Origin 1: exchange interaction
Origin 2: RG NS collision
• RG NS collisions– If RG is massive CE phase can cause inspiral – Otherwise RG envelope is ejected leaving an ecce
ntric WD-NS binary• Subsequent gravitational radiation causes inspiral
Origin 3:
• Descendants of primordial binaries
Belczynski & Taam
Formation channels
UCXB
Galactic SFR ~ 1-3 /yr (Blitz 1997) or 1~10 /yr (Gilmore 2001).Uncertainties:X-ray duty cycle for transients, 33CE evolution (α× λ=0.1), 20 IMF (independent secondary), 10
478*100/33/20/10=7
MM
Calibration
Thanks for your patience!