Letter to the Editor

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

¹ Centro de Astrobiología (CAB), CSIC-INTA, ESAC Campus, Camino bajo del Castillo s/n, E-28692 Villanueva de la Cañada, Madrid, Spain
² European Southern Observatory, Alonso de Cordova 3107, Casilla 19 Vitacura, Santiago, Chile
³ Instituto de Radioastronomía y Astrofísica, Universidad Nacional Autónoma de México, Antigua Carretera a Pátzcuaro 8701, Ex-Hda. San José de la Huerta, 58089 Morelia, Michoacán, Mexico
⁴ Institute of Astronomy, University of Cambridge, Madingley Road, CB3 0HA Cambridge, UK
⁵ Laboratoire d’Astrophysique de Bordeaux, Univ. Bordeaux, CNRS, B18N, allée Geoffroy Saint-Hilaire, 33615 Pessac, France
⁶ Department of Physics, Maynooth University, Maynooth, Co.Kildare, Ireland
⁷ European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany
⁸ Department of Physics, Middlebury College, Middlebury, VT 05753, USA
⁹ Université Paris-Saclay, Université Paris Cité, CEA, CNRS, AIM, 91191 Gif-sur-Yvette, France

^★★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 31 October 2025
Accepted: 2 March 2026

Abstract

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_.^″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 M_Jup. 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.