Limits on binary planets in HR 8799b, c & d

We model radial velocity observations of HR 8799 b, c, and d from Ruffio+ (2021, J/AJ/162/290) and determine upper limits on the msini of short-period binary planets and satellites. At 95% confidence, we rule out companions orbiting the three planets more massive than msini=2M_J_ with orbital periods shorter than 5 days.

We achieve our tightest constraints on moons orbiting HR 8799c, where with 95% confidence we rule out out edge-on Jupiter-mass companions in periods shorter than 5 days and edge-on half-Jupiter-mass moons in periods shorter than 1 day. These radial velocity observations come from spectra with resolution 20 times lower than typical radial velocity instruments and were taken using a spectrograph that was designed before the first directly imaged exoplanet was discovered.