Full width at half maximum of each hydrogen emission line of source 238. The Paschen series is shown in orange, and the Brackett series is shown in blue. The dashed line is before photospheric subtraction, and the solid line is after photospheric subtraction. The Pfund series is shown in green. The dashed line is before photospheric subtraction. The solid line is after photospheric subtraction. The expected instrumental resolution is shown in black. The systematic uncertainty of the spectral resolution is in pale grey. Transition names are indicated. For the Pfund transitions, only n_up is shown for visual clarity.