Journal Article

Two photometric periods in the AM CVn system CP Eridani

E. Armstrong, J. Patterson and J. Kemp

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 421, issue 3, pages 2310-2315
Published in print April 2012 | ISSN: 0035-8711
Published online April 2012 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2012.20463.x
Two photometric periods in the AM CVn system CP Eridani

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We report photometric periodicities in the AM CVn system CP Eridani (CP Eri) of 1716.2 ± 0.2 and 1701.4 ± 0.2 s, obtained while the system was in quiescence. From a second observation obtained during superoutburst, we interpret the 1716-s signal as a superhump period (Psh) and the 1701-s signal as the orbital period (Porb) of the binary. The derived fractional superhump period excess ɛ adds CP Eri to a small collection of AM CVn stars with ɛ measured via time-series photometry of superhump and orbital periods. Plotting ɛ(Porb) for these systems, we find that AM CVn systems may, as expected, be evolving towards longer Porb. We discuss a technique of using ɛ to determine the degree of degeneracy of the donor star in a contact binary, and we show that for the AM CVn systems, the donor stars are well described by mass–radius relations of partially-degenerate objects.

Keywords: accretion, accretion discs; binaries: close; stars: individual: CP Eridani; novae, cataclysmic variables; white dwarfs

Journal Article.  4025 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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