Identification of spectroscopic members from H3 Survey data. The black points denote all H3 objects in the 10° × 10° field of view shown in the top left panel, orange crosses denote PM-selected stars that were specifically followed up for this work, and the red points are our final Specter members. We show the ϕ ₂ = 0 line that defines our great circle coordinate frame. In the top right CMD, we overlay an [Fe/H] = −1.8, 13 Gyr MIST isochrone, as well as the BHB ridgeline from Deason et al. (2011). Our members lie on the same isochrone, have near-identical proper motions and radial velocities, and are systematically metal-poor with spectroscopic [Fe/H] < −1.5. We also show the tentative LAMOST member described in Section 2.3.