We observe G117-B15A, the most precise optical clock known, to measure the rate of change of the main pulsation period of this blue-edge DAV white dwarf. Even though the obtained value is only within 1 σ, P = (2.3±1.4) x 10 -15 s s-ˡ, it is already constraining the evolutionary timescale of this cooling white dwarf star.
The astrophysical journal. Chicago. Vol. 534, no. 2 pt. 2 (May 2000), p. L185-L188