DOI

https://doi.org/10.48717/ethe-pf87

Project

EM186

Title

Disentangling the Ultracool Binary 2MASSJ0423485-041403

Abstract

Ultracool dwarfs bridge the gap between stars and giant exoplanets, making them prime laboratories for studying magnetism, atmospheric dynamics, and rotation. Their auroral radio emission, powered by the electron cyclotron maser instability, provides a unique tool to probe interior rotation, complementing infrared photometry that traces atmospheric cloud structures. In the L6.5+T2 binary system 2MASS J04234858-0414035, previous VLA observations revealed periodic radio bursts with a rotation period of 1.47±0.13 h, while near-infrared monitoring measured 2.0±0.4 h. The discrepancy exceeds minute-scale offsets seen in similar objects, raising the possibility that radio and infrared periods originate from different components of the binary. Preliminary EVN observations at 5 GHz yielded a tentative pulsed detection consistent with the T2 component, though limited sensitivity and uncertainties in the orbital parameters prevented confirmation. We propose a 4-hour, dual-polarization EVN observation to resolve the 160 mas binary. Our goals are to confirm the detection, measure the rotation period, and verify we are detecting the same component reported by Kao et al. (2018). This program will disentangle the system and, for the first time, determine individual rotation periods of the components using multi-wavelength observations.