Atmospheric Waves Driving Variability and Cloud Modulation on a Planetary-Mass Object

TL;DR

This study investigates atmospheric variability in a planetary-mass object at the L/T transition, finding that planetary-scale waves likely drive observed multi-band photometric variability and cloud modulation, with complex vertical cloud structures evidenced by phase shifts.

Contribution

The paper demonstrates that planetary-scale waves are the primary cause of variability in SIMP0136, providing new insights into atmospheric dynamics and cloud behavior in planetary-mass objects.

Findings

Wave models better fit the observed variability across all NIR bands.

Spot sizes required are unphysically large compared to planetary scales.

Detected phase shift indicates complex vertical cloud structure.

Abstract

Planetary-mass objects and brown dwarfs at the transition ($\rm{T}_{eff}\sim1300$\,K) from relatively red L dwarfs to bluer mid-T dwarfs show enhanced spectrophotometric variability. Multi-epoch observations support atmospheric planetary-scale (Kelvin or Rossby) waves as the primary source of this variability; however, large spots associated with the precipitation of silicate and metal clouds have also been theorized and suggested by Doppler imaging. We applied both wave and spotted models to fit near-infrared (NIR), multi-band ($Y$/$J$/$H$/$K$) photometry of SIMP\,J013656.5+093347 (hereafter SIMP0136), collected at the Canada-France-Hawaii Telescope using the Wide-field InfraRed Camera. SIMP0136 is a planetary-mass object (12.7$\pm1.0 \ \rm{M_J}$) at the L/T transition (T2$\pm0.5$) known to exhibit light curve evolution over multiple rotational periods. We measure the maximum peak-to-peak variability of $6.17\pm0.46\%$, $6.45\pm0.33\%$, $6.51\pm0.42\%$, and $4.33\pm0.38\%$ in the $Y$, $J$, $H$, and $K$ bands respectively, and find evidence that wave models are preferred for all four NIR bands. Furthermore, we determine the spot size necessary to reproduce the observed variations is larger than the Rossby deformation radius and Rhines scale, which is unphysical. Through the correlation between light curves produced by the waves and associated color variability, we find evidence of planetary-scale, wave-induced cloud modulation and breakup, similar to Jupiter's atmosphere and supported by general circulation models. We also detect a $93.8^{\circ}\pm7.4^{\circ}$ ($12.7\sigma$) phase shift between the $H-K$ and $J-H$ color time series, providing evidence for complex vertical cloud structure in SIMP0136's atmosphere.