Radio emission in ultracool dwarfs: The nearby substellar triple system VHS 1256-1257

DOI: 
10.1051/0004-6361/201732130
Publication date: 
01/02/2018
Main author: 
Guirado, J. C.
IAA authors: 
Pérez-Torres, M. A.
Authors: 
Guirado, J. C.;Azulay, R.;Gauza, B.;Pérez-Torres, M. A.;Rebolo, R.;Climent, J. B.;Zapatero Osorio, M. R.
Journal: 
Astronomy and Astrophysics
Refereed: 
Yes
Publication type: 
Article
Volume: 
610
Pages: 
A23
Abstract: 
Aim. With the purpose of investigating the radio emission of new ultracool objects, we carried out a targeted search in the recently discovered system VHS J125601.92-125723.9 (hereafter VHS 1256-1257); this system is composed by an equal-mass M7.5 binary and a L7 low-mass substellar object located at only 15.8 pc. <BR /> Methods: We observed in phase-reference mode the system VHS 1256-1257 with the Karl G. Jansky Very Large Array at X band and L band and with the European VLBI Network at L band in several epochs during 2015 and 2016. <BR /> Results: We discovered radio emission at X band spatially coincident with the equal-mass M7.5 binary with a flux density of 60 μJy. We determined a spectral index α = −1.1 ± 0.3 between 8 and 12 GHz, suggesting that non-thermal, optically thin, synchrotron, or gyrosynchrotron radiation is responsible for the observed radio emission. Interestingly, no signal is seen at L band where we set a 3σ upper limit of 20 μJy. This might be explained by strong variability of the binary or self-absorption at this frequency. By adopting the latter scenario and gyrosynchrotron radiation, we constrain the turnover frequency to be in the interval 5-8.5 GHz, from which we infer the presence of kG-intense magnetic fields in the M7.5 binary. Our data impose a 3σ upper bound to the radio flux density of the L7 object of 9 μJy at 10 GHz.
Database: 
ADS
SCOPUS
URL: 
https://ui.adsabs.harvard.edu/#abs/2018A&A...610A..23G/abstract
ADS Bibcode: 
2018A&A...610A..23G
Keywords: 
brown dwarfs;stars: magnetic field;radiation mechanisms: general;techniques: interferometric;Astrophysics - Solar and Stellar Astrophysics