WISEPC J112254.73+255021.5

Radio emission

The object was first detected on 2013 May 8 with the Arecibo at 5 GHz. Five flares were detected in multiple week-long confirmation runs from December 2013 to January 2014. Observations in 2015 did not produce any detections. The magnetic field strength was estimated to be B≥1.8 kG. The pulses have a duration of 30–120 s and show a rapid frequency drift. The pulses are sporadic and have a left circular polarization fraction of 15% to 100%. Analysis of the data found an unusual short period of 17.26 minutes for the flares. This would mean that WISE J1122+25 is highly oblate and near its break-up rate. Observation with the VLA did find a higher rotation period of about 116 minutes and infrared observations with Gemini did not detect variability. This would make the rotation period more similar to rotation periods found in other brown dwarfs. The handedness of the circular polarization changed twice in the VLA observation. This is likely due to the magnetic dipole being highly misaligned with its rotation axis. The brown dwarf was observed with the Very Long Baseline Array over a time-span of one year. This observation showed that the radio emission is compact and highly circular polarized, mostly right-handed circularly polarized (RCP) with some epochs showing evidence of left-handed circularly polarized (LCP) emission. The RCP originate from the northern aurora ring and the LCP originates from the southern aurora ring. The spin axis is inclined by , with the north pole pointing towards earth, explaining the dominance of RCP emission. Unlike previous observations this work finds that the magnetic axis is misaligned with the spin axis by only , which still can explain the switch in handedness of the polarization. The timeseries shows a periodicity of , which is interpreted as the rotation period. Modelling showed that the light curves can be reproduced with electron cyclotron maser emission (ECME) produced in circumpolar auroral rings, similar to oval auroras in Jupiter. The observations also detected a 100% RCP flare on 2022-10-25 (2022.82). The researchers did use astrometry to look for any companions around WISE J1122+25 and exclude companions heavier than Saturn, except for very short periods, such as a hot Jupiter. The observations improved the parallax and proper motion, showing that both the brown dwarf and the star LHS 302 have the same distance and proper motion. The researchers find that WISE J1122+25 may have formed in the circumstellar disk around LHS 302 via disk fragmentation in a wide orbit of

References

References

1. (2011-12-01). "The First Hundred Brown Dwarfs Discovered by the Wide-field Infrared Survey Explorer (WISE)". The Astrophysical Journal Supplement Series.
2. (2017-01-01). "Variable and Polarized Radio Emission from the T6 Brown Dwarf WISEP J112254.73+255021.5". The Astrophysical Journal.
3. (2016-04-01). "Radio Flaring from the T6 Dwarf WISEPC J112254.73+255021.5 with a Possible Ultra-short Periodicity". The Astrophysical Journal.
4. (2021-03-01). "The Field Substellar Mass Function Based on the Full-sky 20 pc Census of 525 L, T, and Y Dwarfs". The Astrophysical Journal Supplement Series.
5. Sanghi, Aniket. (November 8, 2023). "Table of Ultracool Fundamental Properties".
6. (2025). "Main-oval auroral emission from a T6 brown dwarf: Observations, modeling, and astrometry". The Astrophysical Journal.