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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!.

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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




XMM-MSSL polar survey

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)

The X-ray spectra of polars

Long been the subject of great

controversy. Standard model suggests


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)

FO Aqr: X-ray spectrum

Huge absorption dip due accretion ‘curtain’

Evans et al (2004)

Disc accreting binaries




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


Hakala et al (2004)

ULTRA-compact binary: Porb<10min




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)

What is the electric star model?

Sounds far fetched - but!….

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


Have yet to find one but have discovered

lots of flare stars!