IRAM 04191+1522: A compact proto-brown dwarf binary candidate

Context. Very low luminosity objects (VeLLOs) in nearby star-forming regions have been identified as promising proto-brown dwarf candidates, and studying their multiplicity can shed light on the dominant formation mechanism of substellar objects. Aims. Our aim is to study the multiplicity of the VeLLO IRAM 04191+1522. Methods. We obtained 0.89 mm ALMA observations with a very extended configuration that achieved an angular resolution of ∼0$ {{\overset{\prime\prime}{.}}} $04 (6 au at 140 pc). We complemented these data with new VLA observations and ALMA archival data at 1.3 mm. Results. We resolved IRAM04191+1522 into a close binary candidate for the first time. The binary is detected in the ALMA continuum data with a projected separation of ∼80 mas (or 11 au at a distance of 140 pc). The two sources are oriented in the east-west direction, with the eastern component being brighter and more extended than the western one, which is marginally resolved. Analysis of C18O (2-1) archival data revealed gaseous material in rotation around the binary, presumably from a circumbinary disk with ∼27 au of radius centered on the faintest ALMA component. A fit of the position-velocity diagram allowed us to estimate a total dynamical mass for the system of 50 ± 40 MJup. Therefore, we classify IRAM04191 as a tight proto-brown dwarf binary candidate. The VLA data revealed the detection of a single object closer to the western ALMA source with a spectral index consistent with a radio jet.