Using my double PSF-fitting algorithm, I explored HST/ACS mosaic images of the Orion Nebula Cluster (ONC), searching for companions to brown dwarfs. Young brown-dwarf multiplicity is thoroughly underexplored due to their faintness and low sample sizes. In the ONC, I identified seven companions to 75 brown dwarfs at separations > 10 au, a population rarely seen in the field. With my Bayesian demographic analysis, I demonstrated that the companion frequency of brown dwarf primaries in the ONC is in excess of the field, but likely to be dynamically disrupted over the lifetime of the ONC. Therefore, brown dwarf binary systems are more common outcomes of the turbulent fragmentation process than we previously thought, seemingly occurring as frequently as low-mass stars over separations 20-200 au. See De Furio et al. (2022) for more information.

We are planning to apply my same empirical PSF-fitting code to data in NGC 1333 and NGC 2024 to determine if brown dwarf multiplicity is identified in more star-forming regions and if environment plays any role in its formation and evolution.

Fig. 1. From De Furio et al. (2022). I show the binary detections of our survey in the F555W filter. For each panel, the top image is the postage stamp of the HST data, the middle image is our binary PSF best-fit model, and the bottom image is the residual. The binaries are listed from left to right in order of increasing projected separation. Each postage stamp is 21 × 21 pixels across, an angular size of 1.05" × 1.05". The images are displayed with an inverse hyperbolic sine stretch.

As a part of the JWST NIRCam and NIRISS science teams, I led the data analysis for a portion of GTO-1189, searching for a companion to WISE1828, a suspected Y-dwarf binary. I developed empirical PSF models for NIRCam and NIRISS and demonstarted the ability to recover companions down to 0.5λ/D, or ~ 50 milli-arcseconds on the long-wave channel detector of NIRCam. While I found no companion to WISE1828, we set limits down to 0.5 au in separation. On other JWST collaborations, we used my double PSF-fitting algorithm to detect the first Y-Y dwarf binary system, WISE0336, with NIRCam as a part of GO 2473 (co-PIs: Albert, Meyer). With data from GO 2124 (PI: Faherty), I detected the second Y-Y dwarf binary system, WISE1935, with MIRI. These two systems are likely two of the coldest compact objects directly detected outside of the solar system, and demonstrate that multiple formation continues down to the lowest mass we have been able to probe. See Calissendorff, De Furio et al. (2023) and De Furio et al. (2025) for more information.

Fig. 2. From De Furio et al. (2025). Detection of the second Y-Y dwarf binary system ever, WISE1935-1546, using JWST/MIRI. Panels on the left are cutouts from the MIRI data, middle are the models, and right are the residuals. Top row shows the single PSF fit, bottom row shows the double PSF fit. I detected WISE1935B in the F1000W and F1500W filters, at 0.5λ/D and 0.4λ/D, respectively.

I am also co-PI on an HST archival program (AR 17561) to perform a uniform multiplicity survey of the field brown dwarfs observed with WFC3/IR and WFPC2/PC on HST using my double PSF-fitting algorithm. With a sample size > 200, we will perform the largest brown dwarf multiplicity survey to date. In Mehta, De Furio et al. (2025), we demonstrated the ability to resolve companions down to sub-pixel and sub-diffraction limited scales using my PSF-fitting code on WFC3/IR, despite its severe undersampling, a ~3x improvement on past analyses of these data. This survey is ongoing with results expected in 2026. I am interested in applying this technique to large datasets, particularly those taken with Roman and Euclid, to perform the largest brown dwarf multiplicity surveys by multiple orders of magnitude.

Fig. 3. From Mehta, De Furio et al. (2025). PSF-fitting application to WISE0146, a known T9+Y0 binary system. The top row of each panel is a double-PSF fit and the bottom row is a single-PSF fit. The left panel displays the data, the middle panel displays the models, and the right panel displays the residuals. The reduced chi-squared isi 0.73 and 3.22 for the single and double PSF fit, respectively. The cyan circle and red star are plotted at the locations of the primary and companion, respectively, from the double-PSF fit.