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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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slide1

Observations of compact binaries

using XMM-Newton

Gavin Ramsay

slide2

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

slide3

How compact are they?

The Sun!

A compact binary with 2hr orbital period

slide4

Characteristics depend on the magnetic

field of the white dwarf

B<10^4G

B~10^6G

B>10^7G

slide6

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)

slide9

The X-ray spectra of polars

Long been the subject of great

controversy. Standard model suggests

L_soft/Lhard~1/2

slide10

Survey suggests that most polars show

X-ray spectrum consistent to that predicted

by standard model. However….

Ramsay & Cropper (2004)

slide11

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)

slide14

FO Aqr: X-ray spectrum

Huge absorption dip due accretion ‘curtain’

Evans et al (2004)

slide15

Disc accreting binaries

B<10^4G

B~10^6G

B>10^7G

slide16

YZ Cnc: Porb~2.1hrs

Hakala et al (2004)

slide17

YZ Cnc: X-ray spectrum

Hakala et al (2004)

slide18

Evidence for jets?

Model with no-blue shift

Model with blue shift of

1200km/s

Hakala et al (2004)

slide19

ULTRA-compact binary: Porb<10min

Jupiter

Ultra-compact

binary

slide21

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).

slide22

RX J1914+24: spinning up

Ramsay et al (2005)

slide24

What is the electric star model?

Sounds far fetched - but!….

slide26

RX J1914+24: X-ray spectrum

Very odd!

Ramsay et al (2005)

slide27

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!

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