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Magellan AO System $z'$, $Y_S$, and $L'$ Observations of the Very Wide 650 AU HD 106906 Planetary System

We analyze archival data from Bailey and co-workers from the $Magellan$ adaptive optics system and present the first 0.9 $μ$m detection ($z' = 20.3\pm0.4$ mag; $Δz'=13.0\pm0.4$ mag) of the 11 $M_\mathrm{Jup}$ circumbinary planet HD 106906AB b, as well as the 1 and 3.8 $μ$m detections of the debris disk around the binary. The disk has an east-west asymmetry in length and surface brightness, especially at 3.8 $μ$m where the disk appears to be one-sided. The spectral energy distribution of b, when scaled to the $K_S$-band photometry, is consistent with 1800 K atmospheric models without significant dust reddening, unlike some young, very red, low-mass companions such as CT Cha B and 1RXS 1609 B. Therefore, the suggested circumplanetary disk of Kalas and co-workers might not contain much material, or might be closer to face-on. Finally, we suggest that the widest ($a\gtrsim100$ AU) low mass ratio ($M_\mathrm{p}/M_\mathrm{\star} \equiv q\lesssim0.01$) companions may have formed inside protoplanetary disks, but were later scattered by binary/planet interactions. Such a scattering event may have occurred for HD 106906AB b with its central binary star, but definitive proof at this time is elusive.