Journal Article

The changing X-ray light curves of the intermediate polar FO Aquarii

A. P. Beardmore, K. Mukai, A. J. Norton, J. P. Osborne and C. Hellier

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 297, issue 2, pages 337-347
Published in print June 1998 | ISSN: 0035-8711
Published online June 1998 | e-ISSN: 1365-2966 | DOI:
The changing X-ray light curves of the intermediate polar FO Aquarii

More Like This

Show all results sharing this subject:

  • Astronomy and Astrophysics


Show Summary Details


Comparison of five X-ray observations of the intermediate polar FO Aqr reveals that the morphology of the X-ray light curve changes considerably with time. In particular, power spectra of the 1988 Ginga and 1993 ASCA data reveal strong sideband and orbital variations, whereas the 1990 Ginga observation does not. This suggests that the amount of stream-fed accretion varies with epoch, and the system was accreting predominantly from a disc in 1990.

In contrast to other intermediate polars, the X-ray spin-pulse profiles show significant variations between observations, ranging from relatively sinusoidal to sawtooth-shaped at medium energies. During the 1988 and 1990 observations a notch is visible at spin phase zero, due to the presence of an interpulse at phase 0.85, which is absent during the other observations. At lower energies a narrow pulse of emission is seen at spin phase 0.2.

We interpret the pulse profile from the 1990 Ginga observation using a model for accretion from a disc on to a dipolar magnetic field, the axis of which is offset from the white dwarf centre by ∼ 0.15 white dwarf radii. In order to account for the later occurrence of the hardness-ratio maximum in 1988 and 1993, we suggest that the accretion-rate profile changes so that accretion is favoured along the field lines which trail the magnetic pole. This also accounts for the disappearance of the interpulse and notch in 1993.

Keywords: accretion, accretion discs; binaries: close; stars: individual: FO Aqr; novae, cataclysmic variables; X-rays: stars

Journal Article.  0 words. 

Subjects: Astronomy and Astrophysics

Full text: subscription required

How to subscribe Recommend to my Librarian

Users without a subscription are not able to see the full content. Please, subscribe or login to access all content.