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We begin the search for extremely-low mass ($M\leq0.3M_{\odot}$, ELM) whitedwarfs (WDs) in the southern sky based on photometry from the VST ATLAS andSkyMapper surveys. We use a similar color-selection method as the Hypervelocitystar survey. We switched to an astrometric selection once Gaia Data Release 2became available. We use the previously known sample of ELM white dwarfs todemonstrate that these objects occupy a unique parameter space in parallax andmagnitude. We use the SOAR 4.1m telescope to test the Gaia-based selection, andidentify more than two dozen low-mass white dwarfs, including 6 new ELM whitedwarf binaries with periods as short as 2 h. The better efficiency of theGaia-based selection enables us to extend the ELM Survey footprint to thesouthern sky. We confirm one of our candidates, J0500$-$0930, to become thebrightest ($G=12.6$ mag) and closest ($d=72$ pc) ELM white dwarf binarycurrently known. Remarkably, the Transiting Exoplanet Survey Satellite (TESS)full-frame imaging data on this system reveals low-level ($<0.1$%) butsignificant variability at the orbital period of this system ($P=9.5$ h),likely from the relativistic beaming effect. TESS data on another system,J0642$-$5605, reveals ellipsoidal variations due to a tidally distorted ELM WD.These demonstrate the power of TESS full-frame images in confirming the orbitalperiods of relatively bright compact object binaries.

The ELM Survey South. I. An Effective Search for Extremely Low Mass White Dwarfs