Program: GS-2021A-DD-108

A few days ago we discovered a new 22.5 min orbital period detached double white dwarf binary through radial velocity observations. This system is one of the strongest sources of gravitational waves in the milli-Hertz frequency range of the Laser Interferometer Space Antenna (LISA). Here we request 74 min of Directors Discretionary Time to obtain high-speed photometry of this system to search for eclipses, ellipsoidal variations, reflection, and relativistic beaming effects. These data will help us characterize this extraordinary compact binary. If any photometric variability is detected, it will also enable long-term follow-up to constrain its rate of orbital period change, which will enable multi- messenger astrophysics.