A search for photometric variability in the young T3.5 planetary-mass companion GU Psc b

TL;DR

This study investigates the photometric variability of the young planetary-mass companion GU Psc b in the J-band, finding marginal evidence of variability that could be related to atmospheric features, with implications for understanding similar objects.

Contribution

First variability study of GU Psc b, demonstrating potential atmospheric variability and suggesting brown dwarf mechanisms may apply to planetary-mass companions.

Findings

Marginal detection of 4% variability at 6-hour timescale

Variability amplitude and timescale similar to field T dwarfs

Variability suggests atmospheric features like clouds may cause observed changes

Abstract

We present a photometric $J$-band variability study of GU Psc b, a T3.5 co-moving planetary-mass companion (9-13$M_{\rm{Jup}}$) to a young ($\sim$150 Myr) M3 member of the AB Doradus Moving Group. The large separation between GU Psc b and its host star (42") provides a rare opportunity to study the photometric variability of a planetary-mass companion. The study presented here is based on observations obtained from 2013 to 2014 over three nights with durations of 5-6 hr each with the WIRCam imager at Canada-France-Hawaii Telescope. Photometric variability with a peak-to-peak amplitude of $4\pm1$% at a timescale of $\sim$6 hr was marginally detected on 2014 October 11. No high-significance variability was detected on 2013 December 22 and 2014 October 10. The amplitude and timescale of the variability seen here, as well as its evolving nature, is comparable to what was observed for a variety of field T dwarfs and suggests that mechanisms invoked to explain brown dwarf variability may be applicable to low-gravity objects such as GU Psc b. Rotation-induced photometric variability due to the formation and dissipation of atmospheric features such as clouds is a plausible hypothesis for the tentative variation detected here. Additional photometric measurements, particularly on longer timescales, will be required to confirm and characterize the variability of GU Psc b, determine its periodicity and to potentially measure its rotation period.