Optical Variability, Rotation Period and Inclination Angle of the M9.5 dwarf BRI 0021-0214

TL;DR

This study reports the discovery of a 3.052-hour rotation period for the M9.5 dwarf BRI 0021-0214 through optical photometry, revealing insights into its atmospheric variability and magnetic activity, and estimating its inclination angle.

Contribution

First to measure the rotation period and inclination angle of BRI 0021-0214 using optical photometry combined with previous velocity data.

Findings

Detected a 3.052-hour rotation period.

Estimated inclination angle of approximately 52 degrees.

Observed optical variability likely caused by atmospheric dust clouds.

Abstract

We report $I$-band photometric observations of the radio-detected M9.5 dwarf BRI 0021-0214, obtained with the Galway Ultra Fast Imager (GUFI) on the 1.8m Vatican Advanced Technology Telescope VATT at Mt. Graham International Observatory, Arizona. In total, 19 hours of observations over a 73 day baseline were obtained. BRI 0021-0214 was shown to exhibit modulated emission with a period of $ 3.052 \pm 0.004$ hours with a mean amplitude variability of 0.0044 mag. When combined with rotational velocity data obtained from previous work, our newly discovered rotation period gives an inclination angle of 51.7$^{+5.0}_{-4.5}$ degrees for the rotation axis of BRI 0021-0214 relative to our line of sight. Previous studies have reported that the most plausible cause for optical variability from this dwarf is a consequence of suspended co-rotating dust clouds in its atmosphere. However reports of enhanced H$_{\alpha}$ and intermittent coherent radio emission suggest the possibility of auroral activity in its magnetosphere. Further, more coordinated multiwavlength observations of this dwarf could fully resolve the nature of this elusive rapid-rotator object's observational properties.