UV to IR spectrum of J1634+44. The horizontal lines represent the limits and detections in the GALEX FUV (purple) and NUV (dark blue) filters, the UNIONS u (light blue), g (teal), and r (green) filters, the Pan-STARRS i (yellow), z (orange) and y (red) filters, and the UKIRT J filter (dark red). The width of the line shows the wavelength coverage of the filter. The lines with arrows are 3σ upper limits. The lines with shaded regions are detections, where the shaded regions represent 3σ uncertainties. We also plot spectra for an effective temperature of 15 000 K and 35 000 K, which enclose the full range of effective temperatures that satisfy the photometric constraints.