IR light curve of VHS1256-1257b in 2018 & 2020 epochs

We present a new 42hr Hubble Space Telescope (HST) Wide Field Camera 3 G141 spectral time series of VHS1256-1257b, a late L-type planetary-mass companion that has been shown to have one of the highest variability amplitudes among substellar objects. The light curve is rapidly evolving and best fit by a combination of three sine waves with different periods and a linear trend.

The amplitudes of the sine waves and the linear slope vary with the wavelength, and the corresponding spectral variability patterns match the predictions by models invoking either heterogeneous clouds or thermal profile anomalies. Combining these observations with previous HST monitoring data, we find that the peak-to-valley flux difference is 33%{+/-}2% with an even higher amplitude reaching 38% in the J band, the highest amplitude ever observed in a substellar object.