WISEP J060738.65+242953.4: A Nearby. Pole-On L8 Brown Dwarf with Radio Emission

TL;DR

This study characterizes a nearby L8 brown dwarf with unusual low rotation velocity and no optical variability, detecting radio emission and suggesting it is viewed pole-on, providing insights into brown dwarf magnetic activity.

Contribution

It presents multi-wavelength observations of a nearby brown dwarf, revealing its pole-on orientation and radio emission properties, which are novel among similar objects.

Findings

No optical variability detected over 36 days.

Radio emission observed with the lowest luminosity among similar dwarfs.

Low projected rotation velocity suggests pole-on viewing angle.

Abstract

We present a simultaneous, multi-wavelength campaign targeting the nearby (7.2 pc) L8/L9 (optical/near-infrared) dwarf WISEP J060738.65+242953.4 in the mid-infrared, radio, and optical. Spitzer Space Telescope observations show no variability at the 0.2% level over 10 hours each in the 3.6 and 4.5 micron bands. Kepler K2 monitoring over 36 days in Campaign 0 rules out stable periodic signals in the optical with amplitudes great than 1.5% and periods between 1.5 hours and 2 days. Non-simultaneous Gemini optical spectroscopy detects lithium, constraining this L dwarf to be less than ~2 Gyr old, but no Balmer emission is observed. The low measured projected rotation velocity (v sin i < 6 km/s) and lack of variability are very unusual compared to other brown dwarfs, and we argue that this substellar object is likely viewed pole-on. We detect quiescent (non-bursting) radio emission with the VLA. Amongst radio detected L and T dwarfs, it has the lowest observed L_nu and the lowest v sin i. We discuss the implications of a pole-on detection for various proposed radio emission scenarios.