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Context. Deuterium in H-bearing species is enhanced during the early stagesof star formation, however, only a small number of high spatial resolutiondeuteration studies exist towards protostellar objects, leaving the small-scalestructures unrevealed and understudied. Aims. We aim to constrain the deuteriumfractionation ratios in a Class 0/I protostellar object in formaldehyde (H2CO),which has abundant deuterated isotopologues in this environment. Methods. Weobserved the Class 0/I protobinary system [BHB2007] 11, whose emissioncomponents are embedded in circumstellar disks that have radii of 2-3 au, usingALMA within the context of the Large Program FAUST. The system is surrounded bya complex filamentary structure connecting to the larger circumbinary disk. Inthis work we present the first study of formaldehyde D-fractionation towardsthis source with detections of H2CO 3(0,3)-2(0,2), combined with HDCO4(2,2)-3(2,1), HDCO 4(1,4)-3(1,3) and D2CO 4(0,4)-3(0,3). These observationsenable multiple velocity components associated with the methanol hotspots alsouncovered by FAUST data, as well as the external envelope, to be resolved. Inaddition, based on the kinematics seen in the observations of the H2COemission, we propose the presence of a second large scale outflow. Results.HDCO and D2CO are only found in the central regions of the core while H2CO isfound more ubiquitously. From radiative transfer modelling, the columndensities ranges found for H2CO, HDCO and D2CO are (3-8)x10$^{14}$ cm$^{-2}$,(0.8-2.9)x10$^{13}$ cm$^{-2}$ and (2.6-4.3)x10$^{12}$ cm$^{-2}$, respectively,yielding an average D/H ratio of 0.01-0.04. Following the results of kinematicmodelling, the second large scale feature is inconsistent with a streamer-likenature and we thus tentatively conclude that the feature is an asymmetricmolecular outflow launched by a wide-angle disk wind.

FAUST X: Formaldehyde in the Protobinary System [BHB2007] 11: Small Scale Deuteration