The first millimeter detection of a non-accreting ultracool dwarf

P. K. G. Williams, Sarah L. Casewell, Craig Ronald Stark, S. P. Littlefair, Christiane Helling, E. Berger

Research output: Contribution to journalArticlepeer-review

22 Citations (Scopus)

Abstract

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 We also report flux density measurements from unpublished archival VLA data and new optical monitoring data from the Liverpool Telescope.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.
Original languageEnglish
Number of pages6
JournalAstrophysical Journal
Volume815
Issue number1
DOIs
Publication statusPublished - 9 Dec 2015

Keywords

  • Brown dwarfs
  • Radio continuum : stars
  • Stars: individual (TVLM 513-46546)

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