Maser v_3d as a function of r_2d. A model for ﹩{v}_{{\rm{esc}},{\rm{\max }}}﹩ and the corresponding 1σ uncertainty in that model are shown by the red line and shaded region, respectively. Previously reported masers with ﹩{v}_{3{\rm{d}}}\gt {v}_{{\rm{esc}},{\rm{\max }}}﹩ are highlighted by blue markers: IRS 9 (blue square), SiO-16 (blue triangle), SiO-21 (blue diamond), and SiO-25 (blue plus sign). When the HST proper motions are used, only IRS 9 has ﹩{v}_{3{\rm{d}}}\gt {v}_{{\rm{esc}},{\rm{\max }}}﹩.