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[vsnet-preprint 58] HP Librae (= EC 15330-1403)
Superhumps in Cataclysmic Binaries. XXI. HP Librae (= EC 15330-1403)
J. Patterson, R. Fried, R. Rea, J. Kemp, C. Espaillat, D. Skillman,
D. Harvey, D. O'Donoghue, J. McCormick, F. Velthuis, S. Walker, A. Retter,
Y. Lipkin, N. Butterworth, P. McGee, & L. Cook
download/website: http://cba.phys.columbia.edu/publications/
contact: jop@astro.columbia.edu, j.kemp@jach.hawaii.edu
Publications of the Astronomical Society of the Pacific
submitted, August 2001
We report photometry of the helium-dominated cataclysmic variable HP
Librae during 1995-2001. The main photometric signal varies between
1118.89 and 1119.14 seconds, on a timescale of a few years, and displays a
waveform characteristic of "superhumps". After subtracting the main
signal, we found a weak residual signal at 1102.70+-0.05 s, which we
interpret as the underlying orbital period of the binary. The full
amplitude of this putative orbital variation is just 0.005 mag, the
weakest orbital signal yet found in a CV. The 1119 s signal of HP Lib is
a superb match to the well-studied 1051 s superhump of AM CVn, the "mother
of all helium CVs".
The superhump shows no change in amplitude or waveform on any timescale,
and no essential change in period on timescales shorter than ~3000 cycles.
Such great stability makes the star a promising test case for detailed
studies of the underlying spiral structure in the disk, the likely cause
of superhumps. Comparison of orbital and superhump periods for the family
of AM CVn stars supplies evidence that these stars are evolving towards
longer orbital period.
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