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Observations of compact binariesusing XMM-Newton
Gavin Ramsay
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What is a compact binary?
Two stars orbiting around each other on timescales less than ~few hrsOne star a white dwarf the other a starsimilar to the Sun but less massive
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How compact are they?
The Sun!
A compact binary with 2hr orbital period
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Characteristics depend on the magneticfield of the white dwarf
B<10^4G
B~10^6G
B>10^7G
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XMM-Newton
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XMM-MSSL polar survey
Surprise was that so many were inlow accretion states: ~half of the systems
A survey of 40 strongly magnetic binary systems
Not there!Important input for population synthesis models
Ramsay et al (2004)
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EP Dra - an eclipsing polar
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EP Dra - accretion dip and eclipse
Ramsay et al (2004)
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The X-ray spectra of polars
Long been the subject of greatcontroversy. Standard model suggestsL_soft/Lhard~1/2
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Survey suggests that most polars showX-ray spectrum consistent to that predictedby standard model. However….
Ramsay & Cropper (2004)
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EU UMa - shows very little hard X-ray flux
Some systems, however, showemission properties not predicted by the standard accretion model. One proposalis that dense blobs of materialare present in the accretionflow which do not generatehard X-rays. Not clear why some systems have blobs whileothers do not. Not related tomagnetic field strength.
Ramsay et al (2004)
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B<10^4G
B~10^6G
B>10^7G
XMM-Newton observations of Intermediate Polars
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FO Aqr: P_spin=20.9min, Porb=4.9hrs
Evans et al (2004)
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FO Aqr: X-ray spectrum
Huge absorption dip due accretion ‘curtain’
Evans et al (2004)
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B<10^4G
B~10^6G
B>10^7G
Disc accreting binaries
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YZ Cnc: Porb~2.1hrs
Hakala et al (2004)
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YZ Cnc: X-ray spectrum
Hakala et al (2004)
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Evidence for jets?
Model with no-blue shift Model with blue shift of1200km/s
Hakala et al (2004)
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ULTRA-compact binary: Porb<10min
Jupiter
Ultra-compactbinary
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RX J1914+24: Porb 569 sec (9.5min)
Ramsay et al (2005)
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Models fall into accretion and non-accreting model.
Accreting models predict it wouldspin down over time.
Non-accreting model suggests it would spin-up over time (the electricstar model).
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RX J1914+24: spinning up
Ramsay et al (2005)
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Spining up at a rate of 6.6x10^-12s/s
Ramsay et al (2005)
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What is the electric star model?
Sounds far fetched - but!….
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We know it operates on Jupiter
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RX J1914+24: X-ray spectrum
Very odd!Ramsay et al (2005)
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Both ultra-compacts have been discoveredin X-rays. Search for more!
Programme to search for ultra-compactsystems in XMM-Newton and Chandraarchives.
Have yet to find one but have discoveredlots of flare stars!
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Trenholme, Ramsay & Foley (2004)