The first millimeter detection of a non-accreting ultracool dwarf
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The well-studied M9 dwarf TVLM 513–46546 is a rapid rotator (Prot ∼ 2 hr) hosting a stable, dipolar magnetic field of ∼3 kG surface strength. Here we report its detection with ALMA at 95 GHz at a mean flux density of 56 ± 12 μJy, making it the first ultracool dwarf detected in the millimeter band, excluding young, disk-bearing objects. We also report flux density measurements from unpublished archival VLA data and new optical monitoring data from the Liverpool Telescope. The ALMA data are consistent with a power-law radio spectrum that extends continuously between centimeter and millimeter wavelengths. We argue that the emission is due to the synchrotron process, excluding thermal, free–free, and electron cyclotron maser emission as possible sources. During the interval of the ALMA observation that phases with the maximum of the object’s optical variability, the flux density is higher at a ∼1.8σ significance level. These early results show how ALMA opens a new window for studying the magnetic activity of ultracool dwarfs, particularly shedding light on the particle acceleration mechanism operating in their immediate surroundings.
Williams , P K G , Casewell , S L , Stark , C R , Littlefair , S P , Helling , C & Berger , E 2015 , ' The first millimeter detection of a non-accreting ultracool dwarf ' Astrophysical Journal , vol. 815 , no. 1 . DOI: 10.1088/0004-637X/815/1/64
© 2015. The American Astronomical Society. All rights reserved. This work is made available online in accordance with the publisher’s policies. This is the final published version of the work, which was originally published at: https://dx.doi.org/10.1088/0004-637X/815/1/64
DescriptionWe acknowledge support for this work from the National Science Foundation through Grant AST-1008361. Ch.H. acknowledges support from the European Community under the FP7 by the ERC starting grant 257431.
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