Open AccessTwo photometric periods in the AM CVn system CP Eridani
Author(s) -
Armstrong E.,
Patterson J.,
Kemp J.
Publication year - 2012
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1111/j.1365-2966.2012.20463.x
Subject(s) - physics , photometry (optics) , astrophysics , orbital period , stars , astronomy , contact binary , degeneracy (biology) , binary number , radius , white dwarf , binary system , binary star , bioinformatics , arithmetic , mathematics , computer security , computer science , biology
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 ( P sh ) and the 1701‐s signal as the orbital period ( P orb ) 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( P orb ) for these systems, we find that AM CVn systems may, as expected, be evolving towards longer P orb . 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.