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Measuring the evolution of the most stable optical clock G 117-B15A

S. O. Kepler·J. E. S. Costa·B. G. Castanheira·D. E. Winget·Fergal Mullally·R. E. Nather·Mukremin Kilic·Ted von Hippel·Anjum S. Mukadam·Denis J. Sullivan
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Abstract

We report our measurement of the rate of change of period with time dP/dt for the 215 s periodicity in the pulsating white dwarf G 117-B15A, the most stable optical clock known. After 31 years of observations, we have finally obtained a 4 sigma measurement dP/dt_observed = (4.27 +/- 0.80) x 10^{-15} s/s. Taking into account the proper-motion effect of dP/dt_pm = (7.0 +/- 2.0) x 10^{-16} s/s, we obtain a rate of change of period with time of dP/dt = (3.57 +/- 0.82) x 10^{-15} s/s. This value is consistent with the cooling rate in our white dwarf models only for cores of C or C/O. With the refinement of the models, the observed rate of period change can be used to accurately measure the ratio of C/O in the core of the white dwarf.

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S. O. Kepler, J. E. S. Costa, B. G. Castanheira, D. E. Winget, Fergal Mullally, R. E. Nather, Mukremin Kilic, Ted von Hippel, Anjum S. Mukadam, Denis J. Sullivan. 2005-07-20. Measuring the evolution of the most stable optical clock G 117-B15A. https://doi.org/10.1086/497002

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