A search for millimeter emission from the coldest and closest brown dwarf with ALMA

Abstract

Context: WISE J085510.83-071442.5 (W0855) is a unique object: with Teff ca. 250 K, it is the coldest known brown dwarf (BD), located at only ca.2.2 pc form the Sun. It is extremely faint, which makes any astronomical observations difficult. However, at least one remotely similar ultra-low-mass object, the M9 dwarf TVLM 513-46546, has been shown to be a steady radio emitter at frequencies up to 95 GHz with superimposed active states where strong, pulsed emission is observed. Aims: Our goal is to determine the millimeter radio properties of W0855 with deep observations around 93 GHz (3.2 mm) in order to investigate whether radio astrometry of this object is feasible and to measure or set an upper limit on its magnetic field. Methods: We observed W0855 for 94 min at 85.1-100.9 GHz on 24 December 2019 using 44 of the Atacama Large millimeter Array (ALMA) 12 m antennas. We used the standard ALMA calibration procedure and created the final image for our analysis by accommodating the Quasar 3C 209, the brightest nearby object by far. Furthermore, we created a light curve with a 30 s time resolution to search for pulsed emission. Results: Our observations achieve a noise RMS of 7.3 μJy/beam for steady emission and of 88 μJy for 30 s pulses in the aggregated bandwidth (Stokes I). There is no evidence for steady or pulsed emission from the object at the time of the observation. We derive 3 σ upper limits of 21.9 μJy on the steady emission and of 264 μJy on the pulsed emission of W0855 between 85 GHz and 101 GHz. Conclusions: Together with the recent non-detection of W0855 at 4-8 GHz, our constraints on the steady and pulsed emission from W0855 confirm that the object is neither radio-loud nor magnetospherically particularly active.

4 pages, 3 figures, accepted by A&A

References in corpus (19)

• A terrestrial planet candidate in a temperate orbit around Proxima Centauri
• The First Direct Measurements of Magnetic Fields on Very Low-Mass Stars
• Confirmation of the Electron Cyclotron Maser Instability as the Dominant Source of Radio Emission from Very Low Mass Stars and Brown Dwarfs
• Periodic Bursts of Coherent Radio Emission from an Ultracool Dwarf
• Discovery of a ~250 K Brown Dwarf at 2 pc from the Sun
• Rotational Modulation of the Radio Emission from the M9 Dwarf TVLM 513-46546: Broadband Coherent Emission at the Substellar Boundary?
• Strong dipole magnetic fields in fast rotating fully convective stars
• Measuring Magnetic Fields in Ultracool Stars and Brown Dwarfs
• Expanding the Y Dwarf Census with Spitzer Follow-up of the Coldest CatWISE Solar Neighborhood Discoveries
• Comparison of Gaia DR2 Parallaxes of Stars with VLBI Astrometry
• Indications of Water Clouds in the Coldest Known Brown Dwarf
• High Precision Dynamical Masses of Pre-Main Sequence Stars with ALMA and Gaia
• NEOWISE-R Observation of the Coolest Known Brown Dwarf
• Lithium in LP 944-20
• Temperature constraints on the coldest brown dwarf known WISE 0855-0714
• A LOFAR mini-survey for low-frequency radio emission from the nearest brown dwarfs
• Deep $z$-band observations of the coolest Y dwarf
• Physical properties and astrometry of radio-emitting brown dwarf TVLM513-46546 revisited
• The CASA software for radio astronomy: status update from ADASS 2019