HST GO-14241 Direct Imaging Observations of HD106906b

These data are for time-resolved direct-imaging observations of planetary-mass companion HD106906b. The time-resolved photometry results are used in a paper titled "Cloud Atlas: High-precision HST/WFC3/IR Time-Resolved Observations of Directly-Imaged Exoplanet HD106906b". The abstract of the paper is attached here: HD106906b is an ~11 M_Jup, ~15 Myr old directly-imaged exoplanet orbiting at an extremely large distance from its host star. The wide separation (7.11 arcsec) between HD106906b and its host star greatly reduces the difficulty in direct-imaging observations, making it one of the most favorable directly-imaged exoplanets for detailed characterization. In this paper, we present HST/WFC3/IR time-resolved observations of HD106906b in the F127M, F139M, and F153M bands. We have achieved ~1% precision in the lightcurves in all three bands. The F127M lightcurve demonstrates marginally-detectable (2.7 sigma significance) variability with a best-fitting period of 4 hr, while the lightcurves in the other two bands are consistent with flat lines. We construct primary-subtracted deep images and use these images to exclude additional companions to HD106906 that are more massive than 2 M_Jup and locate at projected distances for more than 700 au. We measure the astrometry of HD106906b in two HST/WFC3 epochs and achieve precisions better than 2.5 mas. The position angle and separation measurements do not deviate from those in the 2004 HST/ACS/HRC images for more than 1 sigma uncertainty. We provide the HST/WFC3 astrometric results for 25 background stars that can be used as reference sources in future precision astrometry studies. Our observations also provide the first 1.4 micron water band photometric measurement for HD106906b. Fitting HD106906b's spectral energy distribution to the BT-Settl model shows that the model over-predicts the HD106906b's water absorption depth and the best-fitting value for log g is inconsistent with previous low to intermediate surface gravity assessment. These inconsistencies highlight the challenges in modeling atmospheres of young planetary-mass objects.