Observations of compact binaries using XMM-Newton Gavin Ramsay

What is a compact binary? Two stars orbiting around each other on timescales less than ~few hrs One star a white dwarf the other a star similar to the Sun but less massive

How compact are they? The Sun! A compact binary with 2hr orbital period

Characteristics depend on the magnetic field of the white dwarf B<10^4G B~10^6G B>10^7G

XMM-Newton

XMM-MSSL polar survey Not there! A survey of 40 strongly magnetic binary systems Surprise was that so many were in low accretion states: ~half of the systems Not there! Important input for population synthesis models Ramsay et al (2004)

EP Dra - an eclipsing polar

EP Dra - accretion dip and eclipse Ramsay et al (2004)

The X-ray spectra of polars Long been the subject of great controversy. Standard model suggests L_soft/Lhard~1/2

Survey suggests that most polars show X-ray spectrum consistent to that predicted by standard model. However…. Ramsay & Cropper (2004)

EU UMa - shows very little hard X-ray flux Some systems, however, show emission properties not predicted by the standard accretion model. One proposal is that dense blobs of material are present in the accretion flow which do not generate hard X-rays. Not clear why some systems have blobs while others do not. Not related to magnetic field strength. Ramsay et al (2004)

XMM-Newton observations of Intermediate Polars B<10^4G B~10^6G B>10^7G

FO Aqr: P_spin=20.9min, Porb=4.9hrs Evans et al (2004)

FO Aqr: X-ray spectrum Huge absorption dip due accretion ‘curtain’ Evans et al (2004)

Disc accreting binaries B<10^4G B~10^6G B>10^7G

YZ Cnc: Porb~2.1hrs Hakala et al (2004)

YZ Cnc: X-ray spectrum Hakala et al (2004)

Evidence for jets? Model with no-blue shift Model with blue shift of 1200km/s Hakala et al (2004)

ULTRA-compact binary: Porb<10min Jupiter Ultra-compact binary

RX J1914+24: Porb 569 sec (9.5min) Ramsay et al (2005)

Models fall into accretion and non-accreting model. Accreting models predict it would spin down over time. Non-accreting model suggests it would spin-up over time (the electric star model).

RX J1914+24: spinning up Ramsay et al (2005)

Spining up at a rate of 6.6x10^-12s/s Ramsay et al (2005)

What is the electric star model? Sounds far fetched - but!….

We know it operates on Jupiter

RX J1914+24: X-ray spectrum Very odd! Ramsay et al (2005)

Both ultra-compacts have been discovered in X-rays. Search for more! Programme to search for ultra-compact systems in XMM-Newton and Chandra archives. Have yet to find one but have discovered lots of flare stars!

Trenholme, Ramsay & Foley (2004)