The one that got away: A unique eclipse in the young brown dwarf Roque 12

TL;DR

This paper reports the discovery of a rare deep eclipse in the brown dwarf Roque 12, suggesting a possible companion with eccentric orbit, and discusses the implications for understanding substellar binaries.

Contribution

It presents the first observed eclipse of a bona fide brown dwarf in the Pleiades and constrains the properties of a potential companion using multi-epoch data.

Findings

Deep eclipse of 0.65 mag observed in Roque 12

Tentative radial velocity variations suggest a companion

Constraints on companion mass, orbit eccentricity, and period

Abstract

We report the discovery of a deep, singular eclipse of the bona fide brown dwarf Roque 12, a substellar member of the Pleiades. The eclipse was 0.65mag deep, lasted 1.3h, and was observed with two telescopes simultaneously in October 2002. No further eclipse was recorded, despite continuous monitoring with Kepler/K2 over 70d in 2015. There is tentative (2sigma) evidence for radial velocity variations of 5km/s, over timescales of three months. The best explanation for the eclipse is the presence of a companion on an eccentric orbit. The observations constrain the eccentricity to e>0.5, the period to P>70d, and the mass of the companion to ~0.001-0.04Msol. In principle it is also possible that the eclipse is caused by circum-sub-stellar material. Future data releases by Gaia and later LSST as well as improved radial velocity constraints may be able to unambiguously confirm the presence of the companion. This would turn the system into one of the very few known eclipsing binary brown dwarfs with known age.