Journal Article

Synthetic direct impact light curves of the ultracompact AM CVn binary systems V407 Vul and HM Cnc

M. A. Wood

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 395, issue 1, pages 378-385
Published in print May 2009 | ISSN: 0035-8711
Published online April 2009 | e-ISSN: 1365-2966 | DOI:
Synthetic direct impact light curves of the ultracompact AM CVn binary systems V407 Vul and HM Cnc

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The interacting binary white dwarf (AM CVn) systems HM Cnc and V407 have orbital periods of 5.4 and 9.5 min, respectively. The two systems are characterized by an ‘on/off’ behaviour in the X-ray light curve, and optical light curves that are nearly sinusoidal and which lead the X-ray light curves in phase by about 0.2 in both systems. Of the models that have been proposed to explain the observations, the one that seems to require the least fine-tuning is the direct impact model of Marsh & Steeghs. In this model, the white dwarf primary is large enough relative to the semimajor axis that the accretion stream impacts the surface of the primary white dwarf directly without forming an accretion disc. Marsh & Steeghs proposed that in this situation there could be a flow setup around the equator with a decreasing surface temperature, the further one measured from the impact point. In this study, we estimate the light curves that might result from such a temperature distribution, and find them to be reasonable approximations to the observations. One unexpected result is that two distinct X-ray spots must exist to match the shape of the X-ray light curves.

Keywords: accretion, accretion discs; binaries: close; binaries: general; novae, cataclysmic variables; X-rays: binaries; X-rays: stars

Journal Article.  6188 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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