Polarised radio pulsations from a new T-dwarf binary

Astronomy and Astrophysics, vol. 675, pp. L6

Abstract

Brown dwarfs display Jupiter-like auroral phenomena such as magnetospheric Hαemission and coherent radio emission. Coherent radio emission is a probe of magnetospheric acceleration mechanisms and it provides a direct measurement of the magnetic field strength at the emitter’s location, both of which are difficult to access by other means. Observations of the coldest brown dwarfs (spectral types T and Y) are particularly interesting as their magnetospheric phenomena may be very similar to those in gas-giant exoplanets. Here we present 144 MHz radio and infrared adaptive optics observations of the brown dwarf WISEP J101905.63+652954.2 made using the Low Frequency Array (LOFAR) and Keck telescopes, respectively. The radio data show pulsed, highly circularly polarised emission which yields a rotation rate of 0.32 ± 0.03 h−1. The infrared imaging reveals the source to be a binary with a projected separation of 423.0 ± 1.6 mas between components of spectral type T5.5 ± 0.5 and T7.0 ± 0.5. With a simple ‘toy model’, we show that the radio emission can, in principle, be powered by the interaction between the two dwarfs with a mass-loss rate of at least 25 times the Jovian value. WISEP J101905.63+652954.2 is interesting because it is the first pulsed methane dwarf detected in a low radio-frequency search. Unlike previous gigahertz-frequency searches that were only sensitive to objects with kiloGauss fields, our low-frequency search is sensitive to surface magnetic fields of ≈50 G and above which might reveal the coldest radio-loud objects down to planetary mass scales.

Authors 9

1. Harish K. Vedantham corresponding

   University of Groningen · Netherlands Institute for Radio Astronomy

   Affiliation as printed

   ASTRON, Netherlands Institute for Radio Astronomy, Oude Hoogeveensedijk 4, 7991 PD Dwingeloo, The Netherlands

   Kapteyn Astronomical Institute, University of Groningen, PO Box 72, 97200 AB Groningen, The Netherlands

2. Trent J. Dupuy

   Royal Observatory · University of Edinburgh

   Affiliation as printed

   Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK

3. E. L. Evans

   Royal Observatory · University of Edinburgh

   Affiliation as printed

   Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK

4. Aniket Sanghi

   The University of Texas at Austin

   Affiliation as printed

   The University of Texas at Austin, Department of Astronomy, 2515 Speedway, C1400, Austin, TX 78712, USA

5. J. R. Callingham Aachen Leiden Observatory

   Leiden University · Leiden Observatory · Netherlands Institute for Radio Astronomy

   Affiliation as printed

   ASTRON, Netherlands Institute for Radio Astronomy, Oude Hoogeveensedijk 4, 7991 PD Dwingeloo, The Netherlands

   Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands

6. T. W. Shimwell Aachen Leiden Observatory

   Leiden University · Leiden Observatory · Netherlands Institute for Radio Astronomy

   Affiliation as printed

   ASTRON, Netherlands Institute for Radio Astronomy, Oude Hoogeveensedijk 4, 7991 PD Dwingeloo, The Netherlands

   Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands

7. W. M. J. Best Aachen Leiden Observatory

   Leiden University · Leiden Observatory

   Affiliation as printed

   Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands

8. Michael C. Liu

   University of Hawaiʻi at Mānoa · University of Hawaii System

   Affiliation as printed

   Institute for Astronomy, University of Hawaii, 2680, Woodlawn Drive, Honolulu, HI 96822, USA

9. Philippe Zarka

   Centre National de la Recherche Scientifique · Observatoire de Paris · Laboratoire d’études spatiales et d’instrumentation en astrophysique

   Affiliation as printed

   LESIA, CNRS -Observatoire de Paris, PSL, 92190 Meudon, France