%ABrooks, Hunter%AKirkpatrick, J.%ACaselden, Dan%ASchneider, Adam%AMeisner, Aaron%AFaherty, Jacqueline%ACasewell, S.%AKuchner, Marc%BJournal Name: The Astronomical Journal; Journal Volume: 163; Journal Issue: 2 %D2022%I %JJournal Name: The Astronomical Journal; Journal Volume: 163; Journal Issue: 2 %K %MOSTI ID: 10349772 %PMedium: X %TDiscovery of CWISE J052306.42−015355.4, an Extreme T Subdwarf Candidate %XAbstract We present the discovery of CWISE J052306.42−015355.4, which was found as a faint, significant proper-motion object (0.″52 ± 0.″08 yr −1 ) using machine-learning tools on the unWISE re-processing of time series images from the Wide-field Infrared Survey Explorer. Using the CatWISE2020 W1 and W2 magnitudes along with a J -band detection from the VISTA Hemisphere Survey, the location of CWISE J052306.42−015355.4 on the W1 − W2 versus J − W2 diagram best matches that of other known, or suspected, extreme T subdwarfs. As there is currently very little knowledge concerning extreme T subdwarfs we estimate a rough distance of ≤68 pc, which results in a tangential velocity of ≤167 km s −1 , both of which are tentative. A measured parallax is greatly needed to test these values. We also estimate a metallicity of −1.5 < [M/H] < −0.5 using theoretical predictions. %0Journal Article