Program: GN-2013A-Q-22

We have recently discovered a powerful laboratory for gravitational wave physics, a 12.75 min eclipsing detached binary white dwarf. The system has a gravitational wave strain of 10$^{-22}$, about 10,000 times larger than the Hulse Taylor pulsar, and will come into contact in less than 1 Myr due to loss of energy and angular momentum via gravitational wave radiation. Using Gemini, GTC, and McDonald 2.1m, we have published a preliminary measurement of this system's orbital decay. The major uncertainties in comparing our $\dot P$ measurement with the predictions of general relativity are the unknown contribution of tidal heating and whether or not the system is tidally locked. Thus we propose to obtain Gemini/GMOS high speed photometric observations of J0651 in two epochs (Feb and Apr 2013) to significantly improve our $\dot P$ measurement. We expect the system's time-of-eclipse will shift 20 sec by April 2013, a larger shift will betray the amount of tidal heating. More importantly, we propose to measure the spin rate of the primary white dwarf via the Rossiter-McLaughlin effect using Keck/LRIS spectroscopy. This system's rapid change in orbital period will provide an unprecedented test of tidal physics in merging white dwarfs and test general relativity in a new regime.