Atmospheric spectra of HD 13724. The FWHM of the J23, H23, and K12 IRDIS filters are shown with grey bars (from left to right). The error bars on the H2, H3, K1, and K2 data are present but smaller than the size of the markers on each plot. Top: two best-fitting spectra from BT-Settl 2008 models (Allard et al. 2012) and the Morley et al. (2012) models from the SpeX Prism library are overplotted, and the flux is scaled to match HD 13724 B. Fitting was performed to the IFS and IRDIS data simultaneously. Bottom: comparison of the observed spectrum of HD 13724 B with the two best fit T4 brown dwarf atmos- pheres: 2MASS J10595185+3042059 and SDSSp J092615.38+58720.9 fitted using the splat package (Burgasser et al. 2016).